Natural Killer T Cells Are Critical for Dendritic Cells to Induce Immunity ...

Natural Killer T Cells Are Critical for Dendritic Cells to Induce Immunity in Chlamydial Pneumonia Antony George Joyee1, Hongyu Qiu1, Yijun Fan1, Shuhe Wang1, and Xi Yang1 1

Laboratory for Infection and Immunity, Departments of Medical Microbiology and Immunology, Faculty of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada

Rationale: We previously showed an important role of natural killer T cells (NKT) in skewing the adaptive T cell immunity to Chlamydia pneumoniae (Cpn), an intracellular bacterial lung infection, but the mechanism remains unclear. Objectives: To investigate the underlying mechanism by which NKT modulate T cell responses in chlamydial pneumonia. Methods: We examined the effect of NKT activation in modulating DC function, especially in generating protective immunity against Cpn infection using combination of NKT knockout (KO) mice and specific NKT activation approaches. Measurements and Main Results: We found that NKT activation in vivo after Cpn infection induces phenotypic and functional changes in dendritic cells (DC). DC from NKT-deficient mice showed reduced CD40 expression and IL-12 production, whereas enhancing NKT activation using a-GalCer increased CD40 expression and IL-12 production. Co-culture of DC with NKT enhanced bioactive IL12p70 production by DC in a CD40L-, IFN-g–, and cell–cell contact– dependent manner. Further, co-culture of T cells with DC isolated from infected wild-type (WT) and NKT-deficient mice induced type1 and type-2 responses, respectively, while DC from a-GalCer– treated, infected mice led to enhanced type-1 responses. Moreover, upon adoptive transfer, DC from infected WT mice induced strong type-1 immunity, whereas those from knockout mice induced type-2 responses and increased disease severity upon challenge infection. Conclusions: Our results provide direct evidence of the critical role of NKT activation in the functional modulation of DC for the development of protective immunity in a clinically relevant respiratory infection. Keywords: NKT cells; dendritic cells; infection; Chlamydia; host defense

Natural killer T cells (NKT) are a specialized innate T cell subpopulation capable of recognizing glycolipid antigens presented by a nonclassical MHC class I molecule CD1 (1). The ‘‘classical’’ or ‘‘invariant’’ NKT are characterized by semiinvariant TCR expression (2). A salient feature of NKT is their ability to rapidly produce Th1- (IFN-g) and Th2-type (IL-4 and IL-13) cytokines upon primary stimulation, thus implicating a regulatory role for these cells in the immune responses to various infections (3) and diverse disease conditions such as autoimmunity, type 1 diabetes, and tumor rejection (4–6). It has

(Received in original form April 3, 2008; accepted in final form July 1, 2008) Supported by operating grants from the Canadian Institutes for Health Research (CIHR) and the Manitoba Health Research Council (MHRC) to X.Y. A.G.J. is a recipient of Postdoctoral Fellowship Awards from the International Centre for Infectious Diseases (ICID)/CIHR National Training Program and the MHRC. H.Q. is a recipient of MHRC studentship and a trainee in ICID/CIHR National Training Program. X.Y. is Canada Research Chair in Infection and Immunity. Correspondence and requests for reprints should be addressed to Xi Yang, M.D., Ph.D., Department of Medical Microbiology, Faculty of Medicine, University of Manitoba, Room 523, 730 William Avenue, Winnipeg, MB, R3E 0W3 Canada. E-mail: [email protected] Am J Respir Crit Care Med Vol 178. pp 745–756, 2008 Originally Published in Press as DOI: 10.1164/rccm.200804-517OC on July 2, 2008 Internet address: www.atsjournals.org

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject

Most previous studies on natural killer T cell (NKT)– dendritic cell (DC) interaction focused on the effect of DC on NKT. Limited knowledge on the role of NKT on DC function is from studies using a-GalCer, a model lipid antigen. What This Study Adds to the Field

We show a critical role of NKT in modulating DC function and the type of adaptive T cell responses in a clinically relevant bacterial pneumonia model.

been well established that virtually all mouse (Va14) and human (Va24) invariant NKT can recognize a-galactosylceramide (a-GalCer or aGC), a glycolipid originally extracted from marine sponges (7, 8). Because of their characteristic rapid activation, effector function, and capability to influence other cells (9, 10), NKT represent an important candidate to link innate and acquired immunity. Dendritic cells (DC) are the most efficient antigen-presenting cells (APC), especially in priming T cells (11, 12). Upon exposure to inflammatory or infectious stimuli, immature DC undergo a maturation process involving migration to lymphoid sites, down-regulation of the rate of antigen uptake, and increases in levels of MHC and costimulatory molecules. These changes enable DC to present antigens to naive CD4 and CD8 T cells, thereby promoting adaptive immune responses (11). Importantly, the type of stimulus and the extent of activation determine the program of DC differentiation and the subsequent host immune responses. Recently, the interaction of DC with innate lymphocytes such as NK and NKT cells has been considered to be a major mechanism for the development of immunity that is independent of TLR ligands (13). Limited studies using model antigens suggest that NKT may play a regulatory role in immune responses through modulating DC function (14–16). Indeed, NKT activation by aGC rapidly induced the full maturation of DC in vivo and elicited combined CD4 and CD8 T cell responses to ovalbumin (OVA) challenge (14). Similarly, another study showed enhanced CD4 and CD8 T cell responses to a soluble antigen in the presence of NKT stimulation with aGC through modulating DC function (15). Further, the combinational use of NKT stimulation with aGC and different TLR ligands enhanced the potency of DC to stimulate naive T cells in vitro (16). While these studies showed the effect of NKT activation on DC function using some soluble model antigens for NKT and T cells, the role of NKT in modulating DC function and the underlying mechanisms operative during clinically relevant microbial infections remain to be characterized.

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AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE VOL 178

Chlamydia pneumoniae (Cpn) is an important human pathogen causing a broad range of respiratory diseases like bronchitis, obstructive pulmonary disease, sinusitis, and so on. Further, Cpn has been implicated in the pathogenesis of cardiovascular and neurologic diseases (17–19). To date, there is no vaccine available due to the incomplete understanding of the complex immunologic mechanisms leading to protective immunity and immunopathology. Studies using mouse models of Cpn infection have shown that T cells, especially CD8 T cells, and IFN-g are critical for protection and that type-1 T cell response is essential for host defense (20–22). However, the precise immune mechanisms leading to the development of protective T cell immunity to Cpn infection remain largely unknown. We have recently reported that NKT exert a crucial protective role in host defense against Cpn infection (23). NKT-deficient mice showed exacerbated susceptibility with higher lung pathogen loads and pathology compared with the wild-type (WT) mice. In particular, the comparison of T cell cytokine profiles of Ja18-knockout (KO) (NKT-KO) and the WT mice showed that WT mice, but not the NKT-KO mice exhibited enhanced type-1 response, suggesting that NKT influenced the nature of adaptive T cell responses (23). In the present study, we further investigated the mechanism by which NKT influence T cell immunity through examining the effect of NKT activation in modulating DC function during Cpn infection, using a combination of KO mice, specific cellular activation, and adoptive transfer approaches. We found that NKT induced phenotypic and functional changes in DC after Cpn infection. NKT activation led to enhanced ability of DC for the production of IL-12p70 and polarization of T cell responses. Our overall findings showed that NKT modulate DC function to elicit strong type-1 acquired immune responses, which lead to the enhanced protection against Cpn infection. These findings provide direct in vivo evidence for the effect of NKT-modulating DC function in immunity to an infection. The data from this study were presented in part at the Keystone Symposium on NK/NKT Cell Biology (24).

METHODS Organism The propagation, purification, and infectivity determination of Cpn (AR-39 strain) were performed as described previously (23). Briefly, the infected HL cell monolayers were ultrasonically disrupted and the cell debris was removed by centrifugation. The bacteria were concentrated by high-speed centrifugation, resuspended in sucrose-phosphateglutamic acid (SPG) buffer, and were stored in small aliquots frozen at 2808C until used. The infectivity, as measured by inclusion-forming units (IFUs) of the bacterial preparation, was determined in HL cell culture. Highly purified Cpn elementary body (EB) preparations were obtained by renografin gradient separation. For in vitro antigenic restimulation assays and cytokine induction in culture, a sonicated killed preparation of EBs (SK-EB) was used (23).

Mice C57BL/6 and Balb/c mice were purchased from Charles River Canada (Montreal, PQ, Canada) or bred at the University of Manitoba animal care facility. Breeding pairs of Ja18 KO (NKT-KO) mice with B6 back ground were kindly provided by Dr. Masaru Taniguchi (RIKEN Research Center for Allergy and Immunology, Yokohama, Japan). These mice were generated by specific deletion of the Ja18 (formerly Ja281) gene segment using homologous recombination and aggregation chimera techniques (25). Breeding pairs of CD1d-KO and D011.10 mice with BALB/c background were purchased from The Jackson Laboratory (Bar Habor, ME). These mice were bred and maintained at a pathogen-free animal care facility in the University of Manitoba. Eight- to 10-week-old mice were used in the study. All experiments were done in compliance with the guidelines issued by the Canadian Council of Animal Care, and the animal protocol was approved by the institutional ethical committee. For

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infection, mice were mildly sedated with isoflurane and intranasally inoculated with 3 3 106 IFUs of Cpn in 40 ml of PBS.

a-GalCer Administration a-GalCer (aGC) was provided by Kirin Brewery (Gunma, Japan). Mice received a single intraveneous injection of 4 mg of aGC diluted in a 0.2-ml volume of PBS. Control mice were injected with an identical volume of vehicle solution alone (0.025% polysorbate 20 in PBS). Mice were infected with Cpn 2 hours after aGC or polysorbate injection.

DC Isolation and Cytokine Production Spleens and lungs were harvested from the animals at specified time after infection and processed into single-cell suspensions. Briefly, the spleens were digested in 2 mg/ml collagenase D (Roche Diagnostics, Meylan, France) in RPMI 1640 for 30 minutes at 378C. EDTA at 5 mM was added during the last 5 minutes to disrupt DC–T cell complexes, and the cell suspension was then pipetted up and down several times and filtered. Total splenocytes after RBC lysis with ACK lysis buffer (150 mM NH4Cl, 10 mM KHCO3, 0.1 mM EDTA) were incubated with CD11c microbeads (Miltenyi Biotec, Auburn, CA) for 15 minutes at 48C. The cells were then washed, resuspended in cell separation buffer (Dulbecco’s Phosphate-Buffered Saline [D-PBS] without Ca21 and Mg21 [Sigma] containing 2% FBS and 2mM EDTA) and passed through magnetic columns for positive selection of DC. Lung singlecell suspensions were prepared essentially as described (23). Total lung DC preparations were obtained by CD11c-magnetic microbead selection (Miltenyi Biotec). After passing consecutively through two columns, the collected DC preparations showed greater than 95% purity. DC isolated from different groups of mice were cultured in complete RPMI 1640 medium containing 10% heat-inactivated FBS, 25 mg/ml gentamicin, 2 mM L-glutamine, and 5 3 1025 2-ME (Kodak, Rochester, NY) in 96-well plates at 1 3 106 cells/well for 72 hours, and the supernatants were measured for IL-12p40, IL-12p70, IL-10, and IL-6 by ELISA using unlabeled (capture) and biotinylated (detection) Abs (purchased from BD Pharmingen, San Diego, CA) as previously described (26).

Flow Cytometry To analyze the expression of various surface markers, freshly isolated splenic DC were stained using anti–CD11c-PE, anti–MHC class IIFITC (I-A/I-E), anti–CD40-FITC, anti–CD80-FITC, and anti–CD86FITC or with respective isotype controls (eBioscience, San Diego, CA) in a staining buffer (D-PBS without Ca21 and Mg21 [Sigma, St. Louis, MO] containing 2% FBS and 0.09% NaN3) on ice for 20 minutes in the dark. After staining, the cells were fixed using 2% paraformaldehyde for 1 hour, washed twice, and resuspended in D-PBS with 2% FBS and 1 mM EDTA. The staining for NKT was done by using PE-mCD1d/ PBS57 ligand tetramer (provided by the National Institute of Allergy and Infectious Disease MHC Tetramer Core Facility, Atlanta, GA). The analysis for IFN-g production by NKT was done by intracellular cytokine staining as per the method described previously (23). CD40 ligand (CD40L) expression on NKT was analyzed using allophycocyanin-labeled anti-CD40L (eBioscience). Sample data were collected using a FACSCalibur flow cytometer (BD Biosciences, San Diego, CA) and the data were analyzed using CellQuest software (BD Biosciences).

NKT–DC Co-Culture To isolate NKT, first B cells, CD8 T cells, and other contaminating cells in the total spleen cell suspension were depleted by using a cocktail of biotin-conjugated antibodies against CD45R (B220), CD8, MHC-II, CD11c, Mac-1 (CD11b), Gr-1, and Ter-119, as well as with anti-biotin microbeads and MACS depletion columns (Miltenyi Biotec). Subsequently, NKT were isolated by positive selection after incubating the cells first with PE-labeled CD1d tetramer and then with anti-PE beads (Miltenyi Biotec). The purity of NKT (CD31tetramer 1 cells) was greater than 96%. Purified DC (106 cells) were cultured with NKT (5 3 105) in the presence or absence of SK-EB (104 IFUs) in 96-well plates with or without 50 mg/ml each of anti–IFN-g (R4–6A2) or CD40L (1B1) mAb. Concentrations of IL-12p70 in the supernatants were measured by ELISA. In indicated experiments, NKT and DC were separated in culture using Transwell plates containing a membrane with a pore size of 0.4 mM (BD Biosciences) to prevent contact between these two cells, but still allowing free movement of soluble proteins.

Joyee, Qiu, Fan, et al.: NKT Modulate DC Function in Infection

747 b Figure 1. Altered surface phenotype and cytokine production pattern of dendritic cells (DC) in natural killer T cell (NKT)-knockout (KO) mice after Chlamydia pneumoniae (Cpn) infection. NKT-KO and WT (C57BL/ 6) mice were killed at 3 days after intranasal infection with Cpn (3 3 106 inclusion-forming units [IFUs]). DC were isolated from the spleen using CD11c microbeads and MACS columns as described in METHODS. (A) Cells were stained for surface markers and analyzed using flowcytometry. Expression of MHC II, CD40, CD80, and CD86 on CD11c1 cells (shaded histograms) and isotype control (line) were shown. The mean fluorescence intensity (left) and the percentages of positive cells (right) are indicated. (B) DC purified from KO and WT mice were placed in culture for 72 hours, and the concentrations of IL-12p40, IL-12p70, IL-10, and IL-6 in the supernatants were measured by ELISA. Data show the mean 6 SD. At least three independent experiments with four mice in each group were performed and one representative experiment is shown. *P , 0.05, **P , 0.01, and ***P , 0.001, Student’s t test (WT versus KO mice).

(100 mg/ml) in complete RPMI medium for 48 hours and the concentrations of IFN-g and IL-4 in the supernatants were measured by ELISA. To assess the ability of DC in activating Cpn-specific T cell responses, DC were co-cultured with T cells isolated from Cpnimmunized mice. For immunization, C57BL/6 mice were injected with 107 live Cpn EBs intraperitoneally, and boosted 2 weeks later with the same dose as described (28). One week after the second immunization, T cells were isolated from spleens of the immunized mice using negative selection by depleting non–T cells by using a cocktail of biotin-conjugated antibodies against CD19, DX5, MHC-II, CD11c, Mac-1 (CD11b), Gr-1, and Ter-119, as well as anti-biotin MicroBeads and MACS columns (Miltenyi Biotec). The purity of T cells was between 97 and 98%. DC isolated from Cpn-infected NKT-KO mice and WT mice were co-cultured with the purified T cells (DC to T cells in a ratio of 1:10) in 200 ml complete RPMI medium with or without SK-EB (104 IFUs/ml) in 96-well plates for 48 hours. For measuring intracellular cytokines, monensin was added to the cultures for the last 4 hours to accumulate cytokines intracellularly. The specific cytokine production pattern of CD8 and CD4 T cells were analyzed by intracellular cytokine staining and flowcytometry as described (23). Briefly, cell surface staining was performed as described above followed by fixation and permeabilization using Cytofix/Cytoperm (BD Pharmingen) as per manufacturer’s instructions. The cells were further stained for intracellular cytokines with anti–IFN-g–APC (XMG 1.2) and anti– IL-4–PE (BVD6–24G2) mAbs (eBioscience) or with corresponding isotope control Abs in permeabilization buffer (eBioscience) and analyzed by flow cytometry.

Adoptive Transfer of DC and Challenge Infection For adoptive transfer, splenic CD11c1 DC isolated using MACS CD11c columns were first washed in protein-free PBS and then injected into the tail vein of syngeneic naive WT recipient mice (0.5 3 106 DC/mouse). Two hours after adoptive transfer, the mice were intranasally inoculated with 3 3 106 IFUs of Cpn in 40 ml of PBS. Body weights of the mice before (Day 0) and after inoculation were recorded daily. The mice were killed at a specified time and the lungs were aseptically isolated and processed for quantitatively assessing Cpn in vivo growth as described previously (23).

DC–T Cell Co-Culture The T cell priming ability of the DC was assessed using a DC-CD4 T cell co-culture system as described (27). DC from NKT-deficient CD1 KO and WT Balb/c mice after infection were cultured with CD4 T cells isolated from the spleens of naı¨ve DO11.10 OVA-specific TCR-abtransgenic mice (Balb/c background). CD4 T cells were isolated using negative selection by depleting CD8 and non–T cells using a cocktail of biotin-conjugated antibodies against CD8, CD19, DX5, MHC-II, CD11c, Mac-1 (CD11b), Gr-1, and Ter-119, as well as anti-biotin microbeads and MACS depletion columns (Miltenyi Biotec). The purity of CD4 T cells was about 98%. DC (105 cells/well) and CD4 T cells (106 cells/well) were co-cultured in 96-well plates in the presence of OVA

Histologic Analysis For histologic analysis, the lung tissues were fixed in 10% buffered formalin and embedded in paraffin. The tissue sections were stained with hematoxylin and eosin, and the histologic changes and cellular infiltration were assessed by light microscopy.

In Vitro Restimulation Assays and Cytokine Measurements To analyze for cytokine production, single-cell suspensions were prepared from draining (mediastinum) lymph nodes and cultured at a concentration of 5.0 3 106 cells/ml alone or with SK-EB (105 IFUs/ml). After incubation for 72 hours in a 5% CO2 atmosphere, the supernatants were collected, frozen, and later analyzed for IFN-g and IL-4 by ELISA.

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Statistic Analysis Data were analyzed using unpaired, two-tailed Student’s t test (GraphPad Prism software, version 4, Graph Pad, San Diego, CA). A P value less than 0.05 was considered significant.

TABLE 1. SUMMARY OF DENDRITIC CELL SURFACE COSTIMULATORY/MATURATION MARKERS EXPRESSION IN Chlamydia pneumoniae–INFECTED NATURAL KILLER T CELL–KNOCKOUT AND WILD-TYPE MICE Surface Markers

RESULTS NKT-KO Mice Show an Altered DC Phenotype and Cytokine Production Pattern after Cpn Infection

The functional capacity of DC is largely dependent on their state of maturation and expression of costimulatory molecules. To analyze whether NKT can influence DC maturation status and costimulatory molecule expression after in vivo infection, we examined DC isolated from spleens of Cpn-infected NKTKO (Ja18-KO) mice and the control C57BL/6 mice. After infection (Day 3), DC of NKT-KO mice (KO-DC) exhibited an altered surface expression pattern for the costimulatory/maturation molecules compared with those of WT mice (WT-DC). The KO-DC showed reduced levels of surface molecule expression of MHC-II, CD40, and CD80, but higher CD86 expression, compared with the WT-DC (Figure 1A, Table 1). It is worthy of note that CD40 was the molecule that showed the most significant reduction in the KO-DC (Figure 1A, Table 1) after infection. In contrast, the intrinsic levels of these surface molecules on DC were similar between naı¨ve NKT-KO and WT mice (summarized in Table 2). The cytokine production by DC can profoundly influence the nature of adaptive immune response by T cells (29). IL-12 production by DC is critically important for driving the development of type-1 T cell response. On the other hand, IL-10 and IL-6 production by DC can suppress type-1 T cell responses and also may promote type-2 responses (30–32). Therefore, we examined the spontaneous cytokine production pattern by DC from Cpn-infected NKT-KO and WT mice. The KO-DC produced significantly lower IL-12, especially bioactive IL-12p70, compared with WT-DC (Figure 1B). In contrast, IL-10 and IL-6 production by KO-DC was significantly higher than WT-DC (Figure 1B), demonstrating that NKT deficiency altered the cytokine profile of DC after infection. Further, as observed in splenic DC, pulmonary CD11c1 DC from NKT-KO mice (KODC) also exhibited an altered expression pattern for surface markers and difference in cytokine (IL-12) production compared with those from the WT mice (Table 3). In addition, we also found similar differences in phenotype and cytokine production pattern in comparing DC from infected Balb/c and CD1d-KO (another type of NKT-deficient mice with a Balb/c background) mice (data not shown). Altogether, these data strongly support that NKT play a critical role in influencing the pattern of DC surface marker expression and cytokine production during infection with Cpn. DC IL-12p70 Production Induced by NKT Cells Involves CD40L Expression and IFN-g Production and Is Dependent on Cell–Cell Contact

To examine the molecular basis by which NKT exert stimulatory activity on DC, we first analyzed the expression of CD40 ligand (CD40L or CD154) and IFN-g production by NKT after infection with Cpn. As shown in Figure 2A, CD40L expression was up-regulated on NKT after infection. Intracellular cytokine staining showed significantly enhanced IFN-g production by NKT after Cpn infection (Figure 2B). To directly examine the contribution of CD40L and IFN-g in the modulating effect of NKT on DC, we co-cultured freshly isolated DC from naı¨ve mice and NKT (isolated from naı¨ve or infected mice) in the presence of killed Cpn EBs (SK-EB) and

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MHC-II % MFI CD40 % MFI CD80 % MFI CD86 % MFI

WT

NKT-KO

93.1 6 2.3 787.9 6 26.1

86.5 6 2.8 * 673.2 6 30.0†

49.9 6 3.0 31.6 6 2.5

27.7 6 2.9‡ 20.4 6 2.6‡

67.2 6 4.1 33.2 6 2.7

59.0 6 5.3* 27.8 6 3.7

43.7 6 4.2 28.8 6 3.3

51.8 6 4.6* 37.6 6 2.1†

Definition of abbreviations: MFI 5 mean fluorescence intensity; NKT-KO 5 natural killer T cell–knockout mice; WT 5 wild-type mice. Mice were infected and examined as described in the legend to Figure 1A. Statistical analyses were performed using Students’ t test. Data are presented as mean 6 SD of four mice in each group. One representative of three experiments with similar results is shown. * P , 0.05, NKT-KO versus WT mice. † P , 0.01, NKT-KO versus WT mice. ‡ P , 0.001, NKT-KO versus WT mice.

examined IL-12 production by DC. We found that the level of IL-12p70 dramatically increased in the wells of DC co-cultured with NKT from naı¨ve or infected mice compared with those of DC cultured alone (Figure 3A). NKT from Cpn-infected mice (infection-activated NKT) enhanced IL-12p70 production by DC more effectively than naı¨ve NKT (Figure 3A). It is worth noting that IL-12p70 was not detectable in cultures of NKT alone, with or without Cpn stimulation (not shown). To evaluate the roles of CD40–CD40L interaction and IFN-g on the induction of IL12p70 release by DC, we used blocking Abs for these molecules in the NKT-DC co-culture. Blockade of either CD40L or IFN-g significantly reduced the enhancement effect of NKT on IL12p70 production by DC (Figure 3B). In particular, the blockade of CD40L reduced the MKT-mediated enhancing effect on DC IL-12 release by more than 80%. To investigate the dependence of enhancing effect of NKTmediated DC IL-12p70 production on cell–cell contact, DC and NKT were separated in culture using Transwells containing a 0.4-mm porous membrane that permits free diffusion of proteins but prevents cellular contact. As shown in Figure 3C, increased IL-12p70 release by DC was completely abrogated when physical contact between these cell populations was prevented, demonstrating the critical importance of cell–cell TABLE 2. SIMILAR BASAL LEVEL OF COSTIMULATORY MOLECULE EXPRESSION IN WILD-TYPE AND KNOCKOUT MICE Surface Markers MHC-II % MFI CD40 % MFI CD80 % MFI CD86 % MFI

WT

NKT-KO

86.6 6 1.1 717.7 6 11.6

86.9 6 2.7 716.0 6 15.0

22.6 6 2.8 15.3 6 1.3

22.3 6 1.1 15.5 6 1.7

5.6 6 0.9 10.1 6 1.0

5.8 6 1.1 10.2 6 1.6

6.0 6 1.1 5.5 6 1.5

5.6 6 0.8 5.8 6 0.5

For definition of abbreviations, see Table 1. Expression of surface markers on DC of naı¨ve WT and NKT-KO mice (three mice/group). Data are shown as mean 6 SD.


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TABLE 3. DIFFERENCE IN PULMONARY DENDRITIC CELL COSTIMULATORY/MATURATION MARKER EXPRESSION PATTERN AND IL-12 PRODUCTION BETWEEN Chlamydia pneumoniae–INFECTED NATURAL KILLER T CELL–KNOCKOUT AND WILD-TYPE MICE

For definition of abbreviations, see Table 1. Mice were infected with C. pneumoniae and were killed on Day 3 after infection. Lung DC were isolated from the WT and NKT-KO mice as described in METHODS. CD11c1 lung DC were analyzed for surface molecule expression using flow cytometry and IL-12 production by ELISA. Statistical analyses were performed using Students’ t test. Data are shown as mean 6 SD in each group of mice. A representative experiment of three independent experiments with similar results is shown. * P , 0.05, NKT-KO versus WT mice. † P , 0.01, NKT-KO versus WT mice.

duction by DC, we examined the functional ability of DC from NKT-KO and WT mice in directing T cell responses using two DC–T cell co-culture systems. First, to assess the naı¨ve T cell– priming ability of DC, CD4 T cells isolated from naı¨ve DO11:10 transgenic mice (with TCR specific for OVA peptide) were subjected to co-culture with DC isolated from Cpn-infected WT (Balb/c) and NKT-deficient CD1d-KO mice, in the presence of OVA, and the cytokine production was analyzed. As shown in Figure 4A, WT-DC induced a dominant Th1 (IFN-g), while the KO-DC induced a dominant Th2 (IL-4) cytokine response by antigen-specific CD4 T cells (Figure 4A). Next, we tested the effect of NKT on the ability of DC to activate Chlamydia-specific T cell responses. T cells isolated from Cpn-immunized mice were co-cultured with DC isolated from infected WT and NKT-KO mice in the presence of SK-EB stimulation. Using intracellular cytokine staining, we evaluated chlamydial antigen-specific cytokine production by CD8 and CD4 T cells. We found that WT-DC induced CD8 T cells to produce large amounts of IFN-g, which was significantly higher than that induced by KO-DC (Figures 4B and 4C). Similarly, WT-DC induced more IFN-g–producing CD4 T cells than KODC. In contrast, KO-DC induced more IL-4, but less IFN-g production by CD4 T cells than WT-DC (Figures 4D and 4E). Thus, WT-DC, compared with KO-DC, were more potent in promoting organism-specific type-1 responses by CD8 and CD4 T cells. Taken together, these data show that, after Cpn infection, NKT condition the functional ability of DC to polarize T cells for strong type-1 responses.

contact in this process. Taken together, these data suggest that both cell contact and cytokine mechanisms are involved in NKT modulation of DC responses.

Enhanced NKT Activation In Vivo by a-GalCer Increases CD40 Expression and IL-12 Production by DC and Type-1 T Cell Polarization

Markers/Cytokines MHC-II % MFI CD40 % MFI CD80 % MFI CD86 % MFI IL-12p40, pg/ml 1L-12p70, pg/ml

WT

NKT-KO

90.8 6 2.4 583.0 6 22.1

83.2 6 3.8* 507.0 6 11.3†

52.2 6 5.1 163.3 6 9.0

36.4 6 2.9† 116.5 6 5.6†

37.6 6 2.4 31.2 6 3.5

29.8 6 3.4* 23.9 6 3.2

14.9 15.8 6450 105

23.8 28.0 3880 22

6 6 6 6

1.5 2.0 404 28.0

6 6 6 6

1.9† 2.2† 545† 7.6†

NKT Modulate the Functional Ability of DC to Direct T Cell Responses In Vitro

To examine the functional implication of NKT-mediated differential costimulatory molecule expression and cytokine pro-

To further confirm the findings observed in KO mice, we took an alternative approach to test the role of NKT in modulating the phenotype and function of DC, by way of enhancing activation of NKT using aGC treatment. WT mice were treated with aGC or vehicle 2 hours before Cpn infection. At Day 3

Figure 2. Cpn infection increases CD40L expression and IFN-g production by NKT cells. C57BL/6 mice were infected with Cpn intranasally as described in the legend to Figure 1 and killed after 3 days. (A) CD40L expression by NKT cells after Cpn infection. Splenocytes were stained with PerCep-labeled antiCD3e Ab, PE-labeled mCD1d/PBS57 ligand tetramer and with allophycocyanin-labeled anti-CD40L Ab and analyzed by flow cytometry. Histograms show analysis on NKT (CD31 tetramer1 cells); percentage of positive cells is indicated. (B) Intracellular cytokine staining. Intracellular cytokine staining was performed using Cytofix/Cytoperm kit from BD Biosciences with allophycocyanin-conjugated anti–IFNg Abs or corresponding isotope control. The IFN-g analysis was performed on gated NKT cells.

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Figure 3. Enhanced DC IL-12p70 production induced by NKT cells involves CD40L expression and IFN-g production, and is dependent on cell–cell contact. (A) Effect of NKT on IL-12p70 production by DC. Freshly isolated DC from naı¨ve mice and NKT cells purified from naı¨ve (nNKT) or infected mice (Inf-NKT) were co-cultured in the presence of SK-EB. The concentration of IL-12p70 in 48-hour culture supernatants was determined by ELISA. (B) Effect of blockade of CD40L and IFN-g on DC IL-12 production induced by NKT. DC and NKT cells isolated from Cpninfected mice (Day 3 after infection) were co-cultured in the presence of SK-EB with or without anti-CD40L or anti– IFN-g Abs, as described in METHODS, and IL-12p70 levels in the culture supernatants were analyzed by ELSA. (C) Dependence on cell–cell contact. Purified NKT and DC were cultured together or separated by a 0.4-mm pore-size membrane (Transwell, BD Biosciences, San Diego, CA) in which DC were seeded in the lower chamber, whereas NKT were placed on the top. SK-EB was added to both chambers. Supernatants of NKT-DC co-cultures and Transwell separated cultures were collected and assayed for IL-12 production by ELISA. The results are mean 6 SD. Data are representative of three independent experiments.

after infection, DC from aGC-treated and control mice were analyzed for surface co-stimulatory molecule expression, cytokine production, and for T cell priming ability in vitro. Notably, compared with those from the vehicle-treated control animals, DC isolated from aGC-treated mice showed significantly higher expression of CD40 (Figure 5A, summarized in Table 4). Further, in line with the data from KO mice, enhanced activation of NKT by aGC treatment in turn significantly increased IL-12 production by DC (Figure 5B) while leading to the trend of reduced IL-10 and IL-6 production. Moreover, DC isolated from Cpn-infected mice with aGC treatment showed enhanced ability for inducing OVA-specific Th1 cells (Figure 5C) and activating Cpn-specific type-1 CD8 and CD4 T cell responses compared with those from vehicle-treated mice, in the DC-T cell co-culture system (Figures 5D and 5E). Adoptive Transfer of DC from Infected WT Mice Confers Protective Immunity against Challenge Infection, while Transfer of DC from Infected NKT-KO Mice Promotes Infection

To further test the effect of NKT–DC interaction on DC function in vivo, we performed adoptive transfer experiments with DC isolated from infected WT and NKT-KO mice and examined their capacity in inducing protective immunity against

Cpn infection. DC isolated from the spleens of WT or NKT-KO mice after infection (Day 3) were adoptively transferred intravenously to naı¨ve C57BL/6 mice and the recipients were further challenged with intranasal Cpn infection. Mice that received PBS alone with the same challenge infection were used as controls. We found that mice transferred with WT-DC showed much less body weight loss and faster recovery compared with those without DC transfer. In contrast, recipients of KO-DC showed even more severe weight loss than the control mice (Figure 6A). Consistently, Cpn loads in the lungs of KODC recipients were significantly higher than WT-DC recipients (z 500-fold) and also those without adoptive transfer (z 10fold) (Figure 6B). Note that neither WT-DC nor KO-DC from originally infected mice showed recoverable Cpn in an in vitro culture system (data not shown), and thus the difference in chlamydial growth in the recipients of different DC was unlikely due to DC carrying Cpn. Histopathologic analysis of lung tissues also showed most intense inflammatory and pathologic changes in the lungs of KO-DC recipients among the different groups (Figure 6C). Further, the cytokine production by draining lymph node (LN) cells showed that the mice receiving KODC exhibited a type-2 cytokine pattern with significantly higher levels of IL-4, but lower levels of IFN-g, whereas those receiving WT-DC showed enhanced type-1 responses (Figure 6D). In aggregate, these findings suggest a critical role of


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Figure 4. Differential ability of DC isolated from Cpn-infected NKT-KO and WT mice to direct T cell responses. (A) The T cell– priming ability of DC was assessed using a DC-CD4 T cell co-culture system. Splenic DC from NKT-deficient CD1 KO and WT mice after infection (Day 3) and splenic CD4 T cells from naı¨ve DO11.10 OVA-specific TCR-ab-transgenic mice were isolated as described in METHODS. CD4 T cells (106 cells/well) were co-cultured with DC (105 cells/well) in the presence of OVA (100 mg/ml) for 48 hours. The concentrations of Th1 (IFN-g) and Th2 (IL-4) cytokines were measured by ELISA. (B–E) Differential cytokine pattern of Cpnspecific CD8 and CD4 T cells induced by different DC. DC isolated from NKT-KO mice and WT mice were co-cultured with T cells isolated from Cpn immunized mice and the cytokine pattern of CD8 and CD4 T cells were analyzed by intracellular cytokine staining as described in METHODS. (B) IFN-g production by CD8 T cells; analysis performed on gated CD31 CD81 cells. (C) Graph represents the summary of percentage of IFN-g–positive CD8 T cells in each group. (D) IFN-g and IL-4 production by CD4 T cells. (E) Graphs represent the summary of IFN-g and IL-4 production pattern by CD4 T cells in each group. Data are shown as mean 6 SD. Three independent experiments with three mice in each group were performed, and one representative experiment is shown (*P , 0.05, **P , 0.01, and ***P , 0.001).

NKT in the innate phase in regulating DC to direct protective immune responses against Cpn infection in vivo.

DISCUSSION We demonstrate in this study the critical importance of NKT in the functional development of DC to generate protective immunity to a clinically relevant bacterial pathogen. Our results show that NKT activation in vivo after Cpn infection induces functional changes in DC, which is further translated to the generation of type-1 effector CD4 and CD8 T cells for enhanced immunity against the infection. Indeed, DC isolated from Cpn-infected NKT-KO mice induced a Th2, whereas that

from the WT mice induced a Th1, response in vitro. Further, DC from aGC-pretreated mice showed enhanced ability in polarizing Cpn-specific CD8 and CD4 T cell responses. More importantly, the DC from WT mice, but not NKT-KO mice, induced strong protection upon adoptive transfer, against infection challenge. The finding suggests that NKT-DC crosstalk in vivo after Cpn infection causes a ‘‘type-1 switch’’ on DC, leading to DC1-like cells that promote type-1 T cell immunity. The novelty of our study is that it is the first report providing direct evidence on the role of NKT in modulating DC function resulting in enhanced protective immunity in an in vivo model of infection. We further studied the molecular basis for the functional changes in DC caused by NKT activation. Comparison of DC

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Figure 5. Effect of increased NKT activation by aGC treatment on DC surface marker expression, cytokine production and the ability to direct T cell responses. C57BL/6 mice were given aGC or vehicle injection (intravenously) and infected with Cpn (four mice per group) as described in METHODS. (A) Expression of costimulatory/maturation markers on DC isolated from aGC-treated mice and vehicle-treated (sham) control mice after Cpn infection (Day 3). Shaded histograms show the expression of the respective molecules and lines show the isotype controls. The mean fluorescence intensity (left) and the percentages of positive cells (right) are indicated. (B) Effect of enhanced NKT activation on DC cytokine production pattern. DC isolated from the above-mentioned groups of mice were cultured for 72 hours, and the concentrations of cytokines in the supernatants were measured by ELISA. (C) T cell priming ability of DC. DC isolated from aGC and vehicle treated mice after Cpn infection (Day 3) were co-cultured with CD4 T cells from naı¨ve DO11.10 OVA-specific TCR-ab-transgenic mice in the presence of OVA as described in METHODS, and the concentrations of cytokines in the 48-hour culture supernatants were measured by ELISA. (D and E) DC function in activating Cpn-specific T cells. DC isolated from the above-mentioned different groups of mice were co-cultured with T cells isolated from Cpn-immunized mice and the cytokine pattern of CD8 and CD4 T cells were analyzed by intracellular cytokine staining. (D) Representative flow cytometry images showing analyses performed on gated CD81 and CD4 1 T cells. (E) Graph summarizing flow cytometry data showing percentage of cytokine-positive cells in each group. Data are shown as mean 6 SD. Results of one representative (of three) experiment are shown (*P , 0.05, **P , 0.01, and ***P , 0.001).

Joyee, Qiu, Fan, et al.: NKT Modulate DC Function in Infection TABLE 4. SUMMARY OF DENDRITIC CELL SURFACE MARKER EXPRESSION PROFILE SHOWING THE EFFECT OF INCREASED NATURAL KILLER T CELL ACTIVATION AFTER Chlamydia pneumoniae INFECTION Surface Markers MHC-II % MFI CD40 % MFI CD80 % MFI CD86 % MFI

Sham C. pneumoniae Infection

aGC 1 C. pneumoniae Infection

94.1 6 1.9 790.2 6 14.7

97.0 6 1.1 811.0 6 13.6

48.3 6 2.7 31.4 6 1.8

58.8 6 2.3* 43.1 6 3.7*

67.0 6 2.1 32.8 6 3.0

71.6 6 3.1 35.2 1 3.2

43.0 6 2.5 27.7 6 2.4

44.4 6 2.8 30.5 6 2.7

Definition of abbreviations: aGC 5 a-galactosylceramide; MFI 5 mean fluorescence intensity. Mice were treated as described in the legend to Figure 5A. aGC (aGC 1 Cpn infection) and vehicle treated control (Sham-Cpn infection) mice were compared. Data are shown as mean 6 SD of four mice in each group. Results of one of the two experiments are shown. * P , 0.01.

from NKT-KO mice and the WT controls after Cpn infection revealed that the former displayed significantly lower expression of CD40, but higher expression of CD86. It has been reported that CD40 triggering leads to enhanced cytokine production by DC, most notably bioactive IL-12p70 (33). The role of CD40 signaling in host defense has also been elucidated in some infection models and other diseases (34, 35). However, the reported studies using infection or disease models have mainly focused on the interaction of CD40 and CD40L on APCs and antigen-specific T cells, respectively. The present study suggests the importance of another interface of CD40– CD40L interaction in host defense against an infection. We found significantly increased CD40L expression on NKT in Cpn-infected WT mice (Figure 2A) and lower CD40 expression on DC in the infected NKT-KO mice (Figure 1A). Moreover, DC from infected mice with aGC pretreatment showed higher CD40 expression than those from vehicle-treated mice (Figure 5A). The enhancing effect of NKT on DC CD40 expression is likely important in determining the function of DC to induce protective T cell immunity. Indeed, our results showed that lower CD40 expression was associated with reduced IL-12 production by DC in NKT-KO mice. On the other hand, the increase of CD86 expression on DC in the KO mice argues for a role of this molecule in promoting Th2 response in Cpn infection. While some studies have demonstrated the differential roles of CD40/CD80 and CD86 molecules in Th1 and Th2 responses, respectively (36–38), other studies suggest overlapping functions of these molecules in the process of Th1/Th2 activation and differentiation (39, 40). Although the role of these molecules was not tested directly, the data obtained using this infection model support a paradigm that NKT-DC crosstalk promotes the activation of DC1-like cells, which induce type-1– dominated immune responses, while in the absence of NKT help, DC switch over to a DC-2–like mode to induce type-2– dominated immune responses after infection. One of the key findings in this study is the critical importance of cell–cell contact and CD40L expression and IFN-g production by NKT for the enhancement of bioactive IL-12p70 production by DC after Cpn infection. DC from NKT-KO mice produced much reduced levels of IL-12p70 compared with those

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from WT mice. On the other hand, prior aGC treatment increased IL-12 production by DC after infection. These results were further supported by the findings from experiments using the in vitro NKT-DC co-culture model. We found that the presence of NKT significantly increased the production of IL12p70 by cultured DC (about 10-fold higher than DC cultured alone; Figure 2D). Previous studies using model glycolipid antigens have shown that the up-regulated expression of CD40L and production of IFN-g by NKT is associated with a Th1 response (41–43), while the incompetent induction of CD40L on NKT is associated with a Th2 response (44). After Cpn infection, NKT up-regulate cell-surface CD40L expression and secrete IFN-g (Figure 2). Consequently, DC obtain at least two signals from activated NKT, leading to enhanced IL-12 production. DC-derived IL-12p70 was greatly inhibited by blocking CD40–CD40L interaction in NKT-DC co-cultures, whereas blockade of IFN-g only partially affected the secretion of IL-12. Importantly, we found that these interactions are primarily dependent on direct cell–cell contact and that the cytokine mechanism involved in this crosstalk is secondary to the contact-dependent activation of DC by NKT described here. The initial activation of NKT by DC often involves IL-12 production by DC (45), and therefore, the promoting effect of NKT-derived IFN-g on IL-12 production by DC is in support of the concept of an IL-12/IFN-g–positive feedback for the release of these cytokines (46). It has been shown that NKT increase IL-12R expression, which further enhances the functional capability of NKT to secrete more IFN-g (45). Moreover, activated DC may also produce IFN-g after this interaction, thus further enhancing IFN-g production by NKT (12). In these ways, the bidirectional crosstalk between NKT and DC mutually enhances their functional abilities. Our previous study showed that NKT augment protective immunity against Cpn infection through an IFN-g–biased response, which skewed the direction of adaptive immune responses including CD4 and CD8 T cells to a type-1 pattern (23). In the present study, we elucidated a major mechanism by which NKT function to bridge innate and adaptive immunity to Cpn infection through modulating DC function. Based on our finding, which showed that WT-DC induced robust organismspecific CD8 T cell response, it could be speculated that NKT interaction with DC may be a dominant form of help for the development of CD8 T cell response, which is particularly important for immunity against this intracellular bacterial pathogen (20, 22). We found a marked increase in the proportion of organism-specific IFN-g–producing CD8 T cells upon co-culture with DC from WT mice, but not with those from KO mice. In line with these findings, we also found that DC from aGC-treated mice showed enhanced ability to induce type-1 CD8 T cell response. It has been reported that the nature of DC activation with increased CD40 and IL-12 are important for conditioning DC to induce CTL responses (36, 47). The present data, together with our previous finding showing a diminished CD8 T cell IFN-g production in the NKT-KO mice (23), indicate that NKT activation after Cpn infection promotes strong type-1 CD8 T cell immunity through modulating DC function. While the predominant role of CD8 T cells in immunity against Cpn infection has been supported by several studies (20–22), the current data also suggest the possibility that CD4 T cells also could contribute to the enhancement of type 1 protective immune responses against the infection. Importantly, we showed a disease-promoting effect of DC from NKT-KO mice in the adoptive transfer experiments. This finding demonstrates the critical importance of in vivo NKT–DC interaction, not only for the induction of protective adaptive immunity, but also for averting the development of pathologic

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Figure 6. Adoptive transfer to test DC function in vivo. DC isolated from the spleens of WT (WTDC) or NKT-KO (KO-DC) mice after Cpn infection (Day 3) were adoptively transferred (intravenously) to naı¨ve C57BL/6 mice recipients and challenged with infection (3 3 106 IFUs). Mice that received PBS alone were used as controls (PBS). The body weight changes after infection were monitored daily. Mice were killed at Day 7 after infection and the bacterial loads in the lungs, lung pathologic changes, and cytokine profiles were analyzed as described in METHODS. (A) Body weight loss. (B) Chlamydial organism growth in the lung. (C) Histopathologic analysis of the lung tissue. The hematoxylin and eosin–stained slides were analyzed in 3200 magnification under light microscopy. (D) Cytokine production by draining lymph node (LN) cells. LN cells were cultured with SK-EB and the 72-hour culture supernatants were examined by ELISA. Data are expressed as mean 6 SD. One of two independent experiments with similar results is shown (*P , 0.05, **P , 0.01, and ***P , 0.001).

reactions during Cpn infection. Our results showed that, in the absence of NKT help, the efficacy of DC for inducing type-1 T cell responses is reduced, leading to a ‘‘DC2’’ mode resulting in type-2 responses and pathology. Indeed, upon adoptive transfer, unlike WT-DC recipients that showed much reduced body weight loss and bacterial loads in the lungs compared with the control mice (with no cell transfer), the KO-DC recipients exhibited increased bacterial loads and body weight loss (Figure 6). Similarly, histologic analysis revealed more severe pathologic changes and tissue damage in the lungs of the KO-DC recipients than that in the WT-DC recipients and even control mice. The analysis of cytokine production by draining lymph node cells in the WT-DC recipient mice showed the development of dominant type-1 responses, whereas that of the KO-DC recipient mice showed a dominant type-2 response. Our study represents the first example showing the adoptive transfer of a type of DC not only failed to promote protective immunity, but increased immune pathology in an intracellular bacterial infection. Notably, previous chlamydial studies have shown variable results in DC adoptive transfer experiments, which mainly used bone marrow–derived DC (BMDC) in C. trachomatis infection models (48, 49). For example, vaccination with murine BMDC pulsed

with whole chlamydial organisms induced a protective Th1-type immune response, whereas major outer membrane protein (MOMP)-pulsed DC induced nonprotective Th2-type response (49). Further, it has been shown that IL-12 production is required for chlamydial antigen-pulsed DC to induce protective Th1 response when transferred in vivo (50). In the present study, in comparison with the reported studies using in vitro cultured BMDC, we demonstrate the importance of ‘‘in vivo modification’’ of DC by signals from NKT for subsequent induction of protective type-1 responses against Cpn infection. In a broader sense, our results demonstrate a central role of NKT–DC interaction for further programming of DC to become competent for eliciting strong immunity to fight an infection. The finding has important implications for understanding the cellular mechanisms, especially in the innate phase of infections, contributing to the development of protective immunity. In this model of infection, NKT contribute to the induction of adaptive antigenspecific responses through DC, ultimately promoting the clearance of infection. The results also show that the absence of NKT could even result in the dysfunction of the host cellular machinery to protect against infectious burden due to incompetent or altered activation of DC. This implies that DC, as the key APC, need to


receive signals from other innate cells, such as NKT (as depicted in this case), to become fully functional for the initiation/ polarization of type-1 T cell adaptive immunity. It should be noted that, apart from changing the DC functional properties, activation of NKT in vivo may also trigger a series of cellular activation events, including the activation of other innate cells such as NK cells and macrophages (9), allowing a more functional, yet more complex network of immune components that further leads to improved conditioning of DC to boost T cell immunity. Collectively, these findings suggest the importance of NKT in enhancing functional competence of DC in the generation of protective host immune responses to infections, and the potential for exploitation of NKT-DC crosstalk in the design of immunotherapeutic strategies for the control of infectious diseases. Conflict of Interest Statement: None of the authors has a financial relationship with a commercial entity that has an interest in the subject of this manuscript.

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