involved appears to be the so-called CD4* Th2 subset which produces interleukin-4 (IL-4) and interIeukin-5. (IL-5). In vitro and in vivo experiments have ...
Immunology and Cell Biology (1996) 74, 206-208
The role of Th2 type CD4^ T cells and Th2 type CD8" T cells in asthma KLAUS J ERB and GRAHAM LE GROS The Malaghan Institute of Medical Research. Wellington South, New Zealand Summary The cellular inflammatory responses which arc seen in allergic and asthmatic diseases are viewed as being quite strongly dependent on the activities of T cells and their products. The major T cell subset involved appears to be the so-called CD4* Th2 subset which produces interleukin-4 (IL-4) and interIeukin-5 (IL-5). In vitro and in vivo experiments have indicated that IL-4 is a key regulator in these kinds of immune responses, not only switching B cells to IgE production, but acting on CD4* T cells to drive their development towards a Th2 phenotype. Recent results have shown that the functional phenotype of CD8* T cells can be switched from interferon y production to IL-4 and IL-5 production by the presence of IL-4. This could prove an especially important phenomenon since it is the production of interferon y by CD8 T cells which is seen as necessar>' for protection against virus infection. This short review updates our current knowledge of how IL-4 can act on CD4^ and CD8* T cell subsets in in vivo models of asthma and allergic disease. Key words: allergy. CD4^ lymphocytes. CD8* lymphocytes. IL-4.
Introduction The characteristics of T cell-mediated inflammatory immune responses are dependent on which cytokines predominate during the course of that response. The so called Th2 cytokines, interleukin- {IL-) 4, IL-5. IL-10 and IL-13, are associated with eosinophil. mast cell activation and preferential switching to IgE production, all associated with responses to allergens and metazoan parasites. The ThI cytokines. IFN-y. lymphotoxin. and IL-2, are involved in delayed hypersensitivity responses and cellular responses against intracellular parasites and viruses.' A major research goal has been to identify which hormones or membrane signals determine the pattern of cytokines which are expressed by T cells during an immune response. A breakthrough came with the demonstration that the major cytokine involved in the expression of Th2 cytokines is IL-4.-"'^ IL-4 effects are not limited to CD4^ T cells; IL-4 has also been demonstrated in vitro to switch CDS* T ceils into IL-4, IL-5 and IL-10 production^ and suppress proinflammatory cytokine production by monocytes. These research findings have now focused much research efTort in determining whether IL-4 and its effects on T cells are important to the development of allergies and asthma in humans. This review covers some of the most recent data concerning regulation of T cell immune responses by IL-4 and where this research will lead in the future. Correspondence: Graham Le Gros. The Malaghan Institute of Medical Research, PO Box 7060, Wellington South. New Zealand. Received and accepted 11 January 1996.
CD4* T cells producing IL-4 and IL-5 and their relationship to asthma A key observation linking IL-4 and IL-5 producing T cells to asthma has been the finding that T cells isolated from the brochoalveolar lavage (BAL) fluid of asthmatic individuals predominantly secrete IL-4 and IL-5.'' Eurthermore. biopsy samples from the lungs of allergic individuals also revealed an increase in mRNA for IL-5.^ IL-5 is thought to exert its chemoattractant effects on eosinophils by increasing the levels of the chemokine receptor for eotaxin (C Mackay, unpubl. data, 1995). These data have been used to suggest that the IL-4 and IL-5 produced by CD4" T cells are important in the aetiology of asthma in humans. Eurther evidence comes from an ovalbumin airways challenge model which has been developed in mice.^ This mouse model involves prior sensitization of the mice to ovalbumin by conventional immunization procedures followed by a single airways challenge with ovalbumin. (Some of the features seen in human disease, high IgE levels and massive eosinophilia in the lung are produced following an airways challenge with ovalbumin.) It was demonstrated that treatment of ovalbumin immunized mice with neutralizing anti-IL-5 or depleting anti-CD4 antibodies resulted in total inhibition of the airways challenge-induced eosinophil inflammation in the lung. Eurthermore, purified lung T cells from sensitized, but not control, mice produced IL-4, IL-5 and IL-10 after activation in vitro, suggesting an involvement of IL-4 and IL-5 producing Th2 cells in this mouse airways challenge model for asthma.
T cell subsets in asthma
IL-4 regulates IL-4 and IL-5 production by CD4T cells In vitro experiments using native T cells have clearly demonstrated that T cells activated with antigen or mitogens in the presence of IL-4 develop and IL-4 and IL-5 production profile. IL-4 gene deleted mice have recently been used to assess whether IL-4 has the same role in the ovalbumin airways challenge mode.** Allergen-challenged, IL-4 genedeleted mice had a dramatically reduced level of lung infiltrating eosinophils and a greatly reduced IL-5 secretion compared with the control mice. This result would suggest that the so-called Th2 cytokine immunoregulatory role assigned to IL-4 does operate in an in vivo immune response. The timing of when IL-4 is most important for mediating this effect has been addressed by administering antiIL-4 neutralizing antibodies either before immunization or before an airways challenge with ovalbumin.'' Administering anti-IL-4 neutralizing antibodies at the time of immunization dramatically blocked the eosinophilic inflammation following intranasal rechallenge with ovalbumin. However, administration of IL-4 neutralizing antibodies just before an airways challenge had no effect on eosinophil migration into the lung. Analysis ofthe IL-5producing capacity of the lung T cells also revealed that administration of IL-4 during immunization inhibited the development of IL-5-producing T cells while if administered after immunization but just before an airways challenge the level of IL-5 production was unaffected. These data would suggest that IL-4 is critically important for the generation of IL-4 and IL-5-producing Th2 cells but not for the maintenance or expression of functional activity in vivo. It should be stated that at this point the initial cellular source of the IL-4 is still controversial with mast cells, basophils. CD8^ T cells and CD4* N K l . r cells all being reported to be capable of producing IL-4 under certain conditions. IL-4 and IL-5 producing CD8' T cells in asthma There is now strong epidemiological and clinical evidence to suggest that viral infections can exacerbate the symptoms of asthma."'' ' Paradoxically, a major host response against virus infection is the activation of IFN-y producing CD8* T cells which are thought to be antagonistic to eosinophil activity and are proposed to suppress Th2 immune responses in the lung. Therefore the link between viral infection, CDS" T cell activation and eosinophil accumulation in asthmatics remains unexplained. Recent in vitro evidence indicates that under some circumstances virus-specific CD8 T cells could be switched to the production of IL-5 and therefore could exacerbate the eosinophilic inflammation found in asthma.'- The presence of IL-4 combined with viral peptide stimulation switched the cytokine profile of naive virus peptide specific CD8* T cells from IFN-y production to IL-5 production. Evidence for such a phenomenon occurring in vivo has not been so readily reported.
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Experiments in which lymphocytic choriomeningitis virus {LCMV)-specific T cell receptor (TCR)-transgenic mice are exposed to lung Th2 immune responses to ovalbumin in the lung shows some evidence of having their virus-specific CD8 T cells switched to IL-5 production.'^ Furthermore these mice can subsequently develop an airways cosinophilia when the virus peptide is administered intranasally. Another striking finding was that IFN-y production was decreased in the T cells of these mice. These results have been used to suggest that a Th2 (IL-4 production) immune response to unrelated antigens can modify the functional potential of bystander naive CD8* T cells to the degree that when they meet their own specific antigen in the form of class I MHC-associated virus peptide they produce IL-5 and recruit eosinophils into the lung. In asthmatic individuals, the IL-4 rich lung environment would appear to have all the ingredients necessaryfor switching any virus-specific CD8* T cell response from IFN-y to IL-5 production. Not only would the impaired secretion of IFN-y result in delayed clearance of the virus from the respirators tract, but vims antigeninduced production of IL-5 by lung CD8' T cells would exacerbate the symptoms of asthma by inducing eosinophil infiltration into the airways. Subsequent eosinophil activation and release of eosinophil-derived cationic proteins such as major basic protein would result in a cascade of events leading to the development of airways responsiveness, a characteristic feature of bronchial asthma. Does IL-4 over production lead to the induction of allergic and asthmatic responses in mice It is now commonly accepted that IL-4 is the necessary cytokine which drives that switch of naive CD4* T cells to IL-4 and IL-5 production. It has been known for quite some time that CD8* T cells have the capacity to produce IL-4 under certain conditions; however, it was recently shown that the addition of IL-4 in vitro also induces the switching of CD8* T cells from a Thl to a Th2 phenotype. A number of distinct functional phenotypes have been reported for CD8* T cells activated in the presence of IL-4. some being able to help B cells and being noncytotoxic, some retaining cytotoxic activity and some losing expression ofthe CD8 surface marker.^'^-'^ All reports show that only IL-4 induces this switching process; however, there is controversy about whether IL-4 has this effect on CD8 T cells in vivo and on the phenotype which is produced. In order to address these questions we analysed whether the continued expression of IL-4 in vivo leads to the generation of Th2 type CD8* T cells. For this purpose we analysed the phenotype of CD8' T cells in IL-4 transgenic mice expressing IL-4 under the control of a MHC class I promoter leading to low levels of IL-4 production in virtually all cell types.' ** B cells express high levels of MHC class II and IgGl and IgE serum levels are strongly enhanced in the serum of these mice. Furthermore, the mice have elevated levels of Th2 type CD4* T cells. These results showed that the in vivo overexpression of IL-4 had the expected effects on B cells and CD4*^ T cells.
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Strikingly the total CD8* T cell numbers in these mice are greatly reduced, the residual CD8'^ T cells secreted similar amounts of IEN-y as did CD8*T cells from litter mate control mice when stimulated in vitro with anti-CD3 and IL-2. Very little IL-4 (which is possibly transgenederived) and no IL-5 could be detected. Analysis of the phenotype crosses between IL-4 Tg and TCR Tg mice (MHC class I restricted TCR expressed on CD8* T cells. specific for an LCMV 9 mer peptide) revealed that stimulating CD8^ T cells from double transgenie mice in vitro with virus peptide and lL-2 resulted in the generation of cytotoxic Thl-like CD8* T cells producting IEN-y. Eurthermore, infecting IL-4 transgenie mice with the influenza virus also led to the generation of cytotoxic CD8" T cells. Our results show that the residual CD8* T eells in the IL-4 transgenie mice are cytotoxic and maintain a Th 1 phenotype. We conclude that the systemic expression of IL-4 in the IL-4 transgenie mice is cither insufficient, not high enough or renders the CD8^ T cells unresponsive to IL-4-induced phenotype switching. More data are needed to establish clearly whether a local environment of IL-4 is able to switch CD8* T cells to IL-5 production during a Th2 type immune response in vivo. The experiments with the IL-4 transgenie mice suggest that possibly CD8* T cells need more lL-4 to switch into Th2 type cells than do CD4^ T cells or B cells undergoing isotype switching to IgE. This could help expain why IgE and CD4'^ T cells arc usually readily detectable during a Th2 immune response (such as in allergic disorders) but Th2-type CD8"' T eells are either lacking or are more difficult to detect.
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blocks Th2 cytokine responses. Nature (Lond.). 1993; 362: 245-7. 5 Erard F, Wild MT, Garcia-Sanz JA, Le Gros G. Switch of CD8 T cells to noncytolytie CD8-CD4-eells that make Th2 cytokines and help B eells. 5a"e«ce (Wash. DC). 1993; 260: 1802-5. 6 Bentley AM, Menz G, Storz C el al. Identifieation of T lymphocytes, macrophages. and activated eosinophils in the bronchial mucosa in intrinsie asthma. Am. Rev. Respir. Dis. 1992; 146: 500-8. 7 Robinson D, Hamid A, Ying J el al. Predominant Th2 like bronehoalveolar T lymphocyte population in bronchial asthma, N. Engl. J. Med 1992; 326: 298-304. 8 Nakajima H, Iwamoto I, Tomoe S et al. CD4" T-lymphoeytes and interleukin-5 mediate antigen-indueed eosinophil infiltration into the mouse traehea. Am. Rev. Respir. Dis. 1992; 144: 374-9. 9 Coyle AJ, Le Gros G. Bertrand C el al. Interleukin-4 is required for the induction of lung Th2 mueosal immunity. Am. J. Resp. Cell Mot. Biol. 1995; 13: 54-9. 10 Beasley R. Coleman ED. Hermon ED. Hoist PE. O'Donnel TV, Tobias M. Viral respiratory tract infection and acute exacerbation of asthma in adult patients. Thorax 1988; 43: 679-85. 11 Johnston SL, Pattermore S. Smith G et al. The association of viral infections with longitudinal changes in respiratory symptoms and/or peak ffow recordings in sehool children. Eur Respir. J. 1991; 5: 105-11. 12 Coyle AJ. Erard E. Bertrand C. Walti S, Pircherr H, Le Gros G. Virus speeifie CD8 T eells ean switeh to IL-5 production and induce airway eosinophilia. J. Exp. Med. 1995; 181: 1229-35. 13 Sad S, Marcotte R. Mosmann TR. Cytokine induced differentiation of preeursor mouse CD8' T eells into eytotoxie CDS'^ T eells secreting THl or TH2 cytokines. Immunity 1995; 2: 271-7. 14 Croft M. Carter S, Swain S, Dutton R. Generation of polarised antigen speeifie CD8 etfeetor eells: reeiproeal aetion of IL-4 and lL-12 in promoting type 1 versus type 2 eytokine profiles. / Exp. Med 1994; 180: 1715-28. 1 5 Maggi E, Giudizi M. Biagiotti R et al. Th2 like CD8* T eells showing B eell helper tunetion and redueed eytolytie aetivity in human immunodeficieney virus infection. / Exp. Med. 1994; 180: 489-95. 16 Erb K. Holtsehe T, Muth K. Horak 1, Sehimpl A. T cell subset distribution and B eell hyperreaetivity in miee expressing IL-4 under the control of the MHC elass I regulatory sequences. Eur. J. Immunol. 1994; 24: 1143-7.
