macrophages and y#{246}T cells in influenza virus-in- fected mice depleted of the. CD4' and. CD8' lymphocyte subsets. Microb. Pat/tog. 14, 75-84. 30. Carding,.
Gamma/delta
T lymphocytes
Marianne
Abstract: two distinct lineages
Wallace,*
Miroslav
in viral infections
Malkovsky,*
of Wisconsin Microbiology,
Medical Schoo4 and Wisconsin Regional Primate Research University of Pennsylvania School of Medicine, Philadelphia
resemble
each
progenitors Although other
the
and
differentiate af and
phenotypically
Immunology
func-
tionally, there are some striking differences. Some y T cells recognize, similarly to c4 T cells, peptides presented by major histocompatibiity complex (MHC) proteins or MHC-like molecules. However, there are y T cells that recognize MHC molecules in a fundamentally different manner in comparison with a T cells. Also in contrast to a T lymphocytes, many y T cells are capable of recognizing nonpeptide antigens. Most responses of y#{246} T cells appear to be directed against microbial pathogenic agents
including
bacteria,
parasites,
and
viruses.
In
par-
ticular, the potent cytotoxic responses ofy T cells against cells infected with, for example, herpesviruses or lentiviruses may be essential for the overall antiviral defense of vertebrates. The analysis of antiviral immunosurveillance by y T cells is crucial for understanding the unique biological role of this lymphocyte subset.J. Leukoc. Biol. 58: 277-283; 1995. Key Words: prolferation
gamma/delta .
T
cells
.
viruses
.
cytotoxicity
pathogenesis
INTRODUCTION T lymphocytes express CD3-associated c4 or y6 (or, more rarely, IS or I) T cell receptor (TCR) heterodimers (reviewed in refs. 1-4). After productive rearrangement, the cell surface expression of TCRs is essential for clonally distributed antigen-specific recognition. T cells bearing c4 TCRS frequently recognize allelic variants of major histocompatibility complex (MHC) class I or class II molecules. Since CD4 and CD8 (the surface coreceptors of c4 T cells which bind to constant parts of MHC ciass II and class
I molecules,
respectively)
are
not
frequently
ex-
pressed on mature y#{246} T cells, it is not too surprising that most ‘y T cells neither display alloreactivity nor use classical MHC class I and II molecules as restriction elements. Despite being infrequent, allospecificity for MHC does exist in y T cells [5-9]. However, the molecular nature of the recognition of MHC-encoded determinants by some ‘l’6 T cells is fundamentally different from the recognition by c4 T cells, as they do not require a functioning classical antigen-processing pathway in the stimulator cells to recognize their MHC class I or class II ligands, and peptides do not confer specificity [10]. Also, the topology of the interactions of MHC with c4 or y TCRs is very different [10]. Indeed, y TCRs are much more similar in their complementarity-determining region 3 (CDR3) lengths to immunoglobulins than to cx4 TCRs, supporting the concept of essentially different recognition properties
Wisconsin
of af and y show a marked
into ‘y T cell and
and
R. Cardingt
of Medical
T lymphocyte T cell lineages.
Microbiology
and Simon
*Departmt
cultured
Center,
TCRs [1 1]. response
microbe-associated .y T cells can murine Vy3/V1 in
Comprehensive
Cancer
Madison,
Center,
and
It is noteworthy to
University
Department
that
stimulation
by
of
y#{246} T cells a variety
of
ligands (reviewed in ref. 3). Moreover, recognize self-antigens. For example, the subset responds to a self-antigen present
keratinocytes
[12],
as
well
as
superantigens;
e.g.,
Staphylococcus enterotoxin A-coated cells are lysed by all human Vy9 T cells [13]. It is convenient to refer to distinct mouse y T cell subsets following the Vy segment nomenclature, because of the unique anatomical location, time of appearance in ontogeny, thymus dependence, and TCR repertoires of these subsets (for details see ref. 3). Concerning human 1 T-cell subsets, the the extensive literature
situation is slightly complicated by usage of two distinct nomenclatures as shown in Table 1 [14, 15]. The nomenclature of Huck et al. [14] is used throughout this article. In terms of human y T cell subsets, it is convenient to distinguish the V1 subset (percent of total y6 T cells in thymus, 50-70%; epithelia, 30-60%; blood, 1-20%; proportion in blood declines with age, most cells remain CD45RA positive, and V1 usually pairs with a Vy element other than Vy9) and the V2 subset (percent of total y T cells in thymus, 1-20%; epithelia, 10-30%; blood, 50-90%; proportion in blood increases with age, most cells become CD45RO positive, and V#{246}2 usually pairs with V’y9). For description of human V region specific monoclonal antibodies see refs. 2, 4, and 16. Although ‘y#{246} T cells do share with a T cells ( 1) many cell surface proteins (e.g., CD2, CD3, CD4, CD5, CD7, CD8, CD11b, CD16, CD25, CD26, CD28, CD44, or CD45), (2) ability to secrete lymphokines [e.g., interleukin-2 (IL-2), IL-3, IL-4, IL-5, IL-6, IL-b, interferon-y (IFN-y),
tumor
necrosis
factor-a
(TNF-a),
or
granulocyte-
(GM-CSF)], and (3) function, recent results suggest that there are more profound differences between the two subsets than originally thought. For instance, the sequence variability of the CDR3 region of ‘y#{246} TCR is substantially greater than that of cx TCR or immunoglobulins [1]. This fact, together with the ability to mcdi-
macrophage antigen-induced
colony-stimulating cytotoxic
factor
Abbreviations: APCs, antigen-presenting cells; BAL, bronchoalveolar lavage; CFA, complete Freund’s adjuvant; CVB3, coxsackievirus B3; EBV, Epstein-Barr virus; HHV-6, human herpesvirus type 6; HIV, human immunodeficiency virus; Hsp, heat shock protein; HSV, herpes simplex virus; 1FN, interferon; IL, interleukin; LCL, lymphoblastoid cell line;
MHC,
major
histocompatibility
complex;
virus. Reprint requests: Marianne Wallace, ology and Immunology, University of University Avenue, Madison, WI 53706. ReceivedJune 1, 1995; acceptedJune
Journal
of
Leukocyte
Biology
Volume
Sly,
simian
Department Wisconsin
immunodeficiency
of Medical MicrobiMedical School, 1300
2, 1995.
58,
September
1995
277
shown that they were not constitutively cytotoxic [26]. In ate specific cellular immune functions without a requirement for antigen processing [10, 17] and the capacity to addition, the number of Hsp65 inflammatory macrowas not reduced during the time when y#{246} lymrespond to nonpeptide antigens [18-22], indicates that ‘y#{246}phages phocytes were present in greatest numbers [28], T cells can recognize a wider variety of antigens and have suggesting that y#{246} T cells were not acting to eliminate a unique a3 T cell-complementing (rather than doudamaged (stressed) or infected cells. bling) function in the immune defense mechanisms. Specifically, it appears that in many situations, y T Further insights into the possible role of y T cells in lymphocytes
could
recognize
the
invading
pathogens
and
this virally from the virus-primed
neoplastic or damaged cells directly (without specialized activities of antigen-presenting cells, such as dendritic or B cells, or macrophages), which would increase the speed and flexibility of host immune defense. In this article, we have attempted to summarize and analyze the role of y#{246} T cells in antiviral immunosurveillance.
MURINE y#{246} T CELL RESPONSES INFECTION The function defense has eral studies cytes
are
a
substantial
component
virus
In adult (A/HKx31;
C57BL6/J x31)
mRNA
were
mice influenza
prevalent
rus-specific sponse.
virally
studies
late
Some of the most comT cells in virus-initiated studies of the murine in ref. 23).
intranasally with H3N2 cells expressing TCR-y
in
bronchoalveolar
the
lavage
(BAL) between day 10 and day 13 postinfection, several days after infectious virus is cleared from the lung (days 7 to 8). The involvement of these y&-TCR mRNA lymphocytes was shown to be staged, with the predominant TCRVy phenotype changing from Vy4 to Cy4 (Vyl) between days 10 and 13 after infection [24]. The y& T cell population isolated 10 days after infection with virus contained cells of granulai morphology [25] and a substantial number of cells with increased DNA content [26]. These features are consistent with the in vivo activation of BAL y T cells, presumably as a consequence of antigen recognition [26]. Furthermore, the appearance of Cy4, V’y1 cells was paralleled by increasing numbers of macrophages expressing a gene encoding the endogenous Hsp65 [24], the putative target for a panel of Vy1Cy4V6.3 TCR murine hybridomas [27]. Although these observations were consistent with the BAL ‘y T cells functioning to kill Hsp inflammatory macrophages, analysis of BAL y#{246} T cells recovered directly from the virus-infected lung for ligand-dependent lytic function has
TABLE
Huck Strauss
et al. et al.
1.
Sequence
of
Human
TCR
y Gene
Elements
virus
[24].
on
Huck
et al. et a!.
Journal
cells during the primed
the
primary
site
was
most
that
the
majority
Second,
of pathology
ofy#{246}T cells
apparent not
it has
7 (the
Six
are
vire-
that
accumu-
after been
present
the possible
Pseudogenes
Are
virus was eliminated to demonstrate any
Denoted
by
w)
Vyl
Vt2
V1’3
V,4
Vy5
Vy5
Vg6
V7
Vg8
VgA
Vyl.1
Vyl.2
Vy1.3
Vyl.4
Vyl.5
Vyl.5
Vyl.6
Vyl.7
Vyl.8
VyA
y
y
y
y
Vy9
VylO
VyB
Vyl 1
JyP1
JyP
Jyl
Cyl
JyP2
Jy2
C
V2
V1’S
VyB
Vi
Jyl.1
Jyl .2
Jyl .3
Cyl
21
J’2.3
C12
‘I’
278
suggest
in the
Chromosome
‘I,
Strauss
“memory” when
as a consequence of the concurrent involvement of a TCR effector cells and that a circuit involving the af and y#{246} T cells and macrophages is important in controlling the development, progression, and/or resolution of the inflammatory immune response to the virus [28]. Experimental evidence in support of y#{246} T cells functioning as part of such a circuit has been obtained from the analysis of cytokine mRNA [30] and protein [31] production by ‘y#{246} T cells within the infected lung. BAL-yS were shown to be a rich source of the imniunoregulatory cytokines IL-4, IL10, and IFN-y which are known to promote B cell growth and antibody synthesis [32], down-regulate the activity of antigen-specific c4 T cells [33], and promote or maintain macrophage activation, respectively. Thus, virus-induced Y T cells may play an indirect yet important role in the immune response by enhancing the generation of B cells capable of producing neutralizing antibody, limiting the development of chronic inflammation and the emergence of potentially autoreactive af3 T cells, and helping to protect the repairing lung from secondary bacterial infection after the virus has been eliminated and virus-specific CD4 and CD8 #{128}43 T cells are no longer being stimulated. Four additional lines of evidence suggest that the involvement of y#{246} T cells may not be particularly related to the nature of the infecting pathogen and that this immune cell circuit is likely to be a feature of many viral, bacterial, and parasitic infections. First, the accumulation of ‘yb. T cells in the lungs of mice infected with influenza
induced
infected virus,
y T However,
encell but
c4 T cells were depleted from such mice, by in vivo administration of anti-CD4 and anti-CD8 antibodies, the accumulation of both the Hsp65 mRNA macrophages and the TCR-’yS mRNA lymphocytes was greatly decreased [29]. These
antiviral immune Nevertheless, sevthat y T lymphoof
inflammatory immune responses. pelling evidence for a role for y immune responses comes from influenza virus model (summarized
Influenza
H1N1 influenza type A virus (A/PR/8/34) greatly hanced both the rapidity and magnitude of the ‘y T response for mice primed with x31 influenza virus not with an influenza B virus (B/HK). This observation was consistent with the generation of influenza A
TO VIRAL
of y T cells in the host not been precisely defined. have clearly demonstrated
mediated inflammatory response have come analysis of the secondary response in influenza mice [28, 29]. Secondary challenge with an
of Leukocyte
Biology
Volume
58, September
1995
virus specificity among BAL y#{246} T cells. Third, of CD4 and CD8 #{128}43 T cells, which would to both prolong the presence of infectious crease
the
possibility
of
secondary
the removal be expected virus and in-
bacterial
infections,
inhibits both the expression of Hsp and y T cell involvement [28]. Fourth, a similar pattern of y T cell involvement has also been demonstrated in the inflammatory immune reaction in the lungs of animals infected with an unrelated respiratory virus, Sendai virus [34, 35] (see below). Thus, any pathogen that is able to trigger the expression
of
either
endogenous
exogenous (bacteria, mal consequence sponse
may
be
(e.g.,
viruses
or
bacteria)
or
fungi, etc.) Hsp expression as a norof the pathogen-specific #{128}43 T cell re-
able
to
invoke
the
involvement
of
y
T
cells.
Sendai As
with
virus the
staged
involvement
of y
T cell
subsets
in
the
immune response to influenza virus, two studies of the y T cell response to Sendai virus have demonstrated that their involvement is restricted to certain stages of the pulmonary immune response [34, 35]. Although differences in the kinetics of y T cell accumulation were seen in these studies, which may have been related to the differences in the virulence of the virus stocks used [35], the results had several common features. Both studies demonstrated the involvement y cells expressing putative Hsp65-reactive receptors (Cy4, Vyl/2, V6) and the expression of Hsp65 or related proteins in macrophages. Data of Hou et al. [34] showed that, as seen in influenza virus infection, the expression of both the y#{246} TCR and Hsp65 was dependent on the presence of CD4 and CD8 T cell subsets. In addition, macrophages from infected, but not control uninfected, mice could induce the expansion of y T cells in vitro [35]. However, as both studies determined that the kinetics of expression of Hsp65 in macrophages and Vy1/2 y cells were not entirely synchronous, with Hsp65 expression either preceding or persisting
after
significance
Coxsackievirus
the
appearance
of this
reactivity
of
this
subset
of
y
cells,
the
observed in this animal group compared with controls. The involvement of the y#{246} T cells isolated from CFA-exposed animals in the pathogenicity of the H31OA1 CVB3 variant was confirmed by adoptive transfer experiments [37].
Herpes
A cytotoxic
virus
Vyl .2/V8
T cell
clone
isolated
nodes mouse scribed
of a herpes simplex virus (HSV) and specific for HSV glycoprotein [38]. To mediate its lytic effect,
nated
Tg14.4)
does
class I or II As Sciammas
on
not
require
the
HSV glycoprotein and coinvestigators
from
lymph
type 1-infected I has been dethis clone (desig-
expression
of
MHC
I-positive target cells. [17] further charac-
terized Tg14.4, it became clear that this T cell clone did not fit the profile of MHC-restricted cytotoxic T lymphocytes because effective HSV glycoprotein I presentation on antigen-presenting cells occurred independently of classical antigen processing pathways-a situation similar to that of IEkspecific or TL1 0b a2 domain-specific y#{246} T cell clones [10]. Sciammas et al. [17] further demonstrated that TgI4.4 cells could recognize whole, unprocessed HSV glycoprotein I adsorbed to the plastic surface of the wells of a microtiter plate.
HUMAN y T CELL INFECTION Epstein-Barr De
(EBV) These
lescent
RESPONSES
TO VIRAL
virus
Paoli
creased ripheral
assessed
is unclear.
simplex
and number blood
coinvestigators
infection cells
in
remained
phase with
[39]
comparison at
the
pan
observed
with
elevated
of infection.
have
of y6 T cells in acute Epstein-Barr
and percentage of patients with
levels
The reactive
y y
healthy during
T cell T
cell
[40] and the V#{246}l-J#{246}l and V#{246}l-J#{246}2 specific [41]. Most y T cells were not reactive
an inthe pevirus controls.
the
conva-
percentage antibody
was TCR1
TCS1 #{246}TCS1 antibody, suggesting that they may belong to the V2 T cell subset, although this was not directly addressed. Furthermore, in comparison with y#{246} T cells from healthy control donors, substantially more y T cells from pa-
B3
antibody with the
Huber [36] reported that coxsackievirus B3 (CVB3)-infected myocytes were lysed by splenic T cells of mice immunized with CVB3. These splenic T cell preparations were also able to lyse allogeneic CVB3-infected targets, tients acutely infected with EBV coexpressed HLA-DR but to a lesser degree than infected syngeneic target cells. and CD38, consistent with being activated in vivo. In experiments using effector populations that were subVy9/V2 T cell reactivities (cytotoxicity and proliferalion) toward the EBV-associated Burkitt’s lymphoma-dejected to selective lymphocyte depletion, both y#{246} and #{128}41 T cell subsets were shown to contribute to cytotoxicity rived cell line Daudi have been among the most against CVB3-infected cells. Although there is no direct intensively characterized y T cell responses [22, 42-48]. This response is clearly mediated through the V’y9/V2 evidence to support the idea that Hsp(s) may be recogTCR [22]. Studies with the Hsp6O family-specific antibodnized by some of these effector T cells, it is possible that the CVB3-induced up-regulation of Hsp7O expression in ies, which can block outgrowth of this T cell subset in myocardial cells [36] may be important in the T cell reresponse to irradiated Daudi cells, indicate a role for this molecule in target cell recognition [43, 46, 48]. It is notesponse to CVB3. The H3 (highly pathogenic) CVB3 variworthy that a proportion of human peripheral blood and ant induced the in vivo appearance of y T cells, which exhibited cytotoxicity the H31OA1 (poorly
for CVB3-infected pathogenic) CVB3
myocytes, variant did
but
synovial
not
response to stimulation with autologous or allogeneic EBV-transformed B lymphoblastoid cell lines (LCLs) [47, 49]. The stimulatory ligand appears to be of cellular (rather than viral) origin [47], and the proliferative response is dependent on direct contact between the responder and stimulator LCL cells and independent of the y chain coexpressed with V61 [49].
[37]. However, treatment of mice with complete Freund’s adjuvant (CFA) 5 days prior to H31OA1 infection promoted the development of myocarditis in these animals. Interestingly, if the CFA-primed mice were treated with antibody directed against the ‘y TCR 2 days prior to H31OA1 infection, a marked decrease in myocarditis was
tissue-derived
Wallace
et a!.
V1
T lymphocytes
Gamma/delta
T cells
proliferate
and
viruses
in
279
Herpes
simplex
virus
Maccario et al. [50] have which have the ability to plex virus type 1 (HSV-1) cells, selectively outgrow clear cell samples isolated when stimulated in vitro hyde-fixed HSV-1-infected also shown that these cells is not
restricted
to
any
(practically 57-62].
always >2 in HIV-negative controls) [55, asymptomatic HP/-infected individuals, frequently about 65% of total peripheral blood ‘y#{246} T cells are v1+, whereas in symptomatic patients this percentage increases to approximately 75% [61, 62]. The increase in Vol+ cells does not seem to correlate with high levels of HIV-1 antigenemia [57]. The VP cells were shown to coexpress HLA-DR [59], CD8 [57, 60], and CD38 [62] and to display enhanced IL-2-mediated outgrowth in vitro in comparison with V#{246}l#{247} cells from HIV-seronegative donors [62], whereas peripheral V’y9 (most often pairs with V62) T cells from HIV-1--seropositive persons did not express the HLA-DR or IL-2 receptor molecules [55], which is indicative of resting T lymphocytes. The augmented peripheral blood representation of the Vol T cell subset was ( 1 ) independent of particular ‘y chain expression, (2) not correlated with CDR3-dependent Vol selection [61, 62], and (3) not associated with any particular junctional motifs [62]. With the exception of one HIVpositive donor [61], the data do not suggest that increases in the Vol subset result from clonal expansions in response to HIV infection [61, 62]. In light of these data, it
demonstrated that y#{246} T cells, recognize and lyse herpes simand type 2 (HSV-2)-infected in peripheral blood mononufrom HSV-positive donors with autologous paraformaldemononuclear cells. They have possess cytotoxic activity that
HLA-A,
-B,
-C,
-DR,
or
-DQ
mole-
cules [50]. These results were confirmed and extended by Bukowski and colleagues [51], who reported that Vy9/V2 T cells were preferentially stimulated to outgrow 4- to 28-fold from PBMCs of HSV-seropositive mdividuals cultured with autologous HSV-infected PHA blasts. ‘y T cells from these cultures lysed HSV-infected but not mock infected targets in an MHC-unrestricted manner. The investigators were able to block the cytotoxicity using monoclonal antibodies (mAbs) to both CD3 and y#{246} TCR. Intriguingly, these investigators observed that the cytotoxic y T lymphocytes were also able to recognize and lyse target cells infected with the unrelated vaccinia virus. They have hypothesized that the y#{246} T cell response may be directed against a cellular ligand induced or modified by acute infection with various unrelated viruses [51]. Finally, they have reported that infection of LCLs with HSV does not lead to induction of cell surface Hsp6O or Hsp7O and that the observed cytotoxicity against HSV-infected targets is not blocked by antisera
Human
to
these
virus
The most comprehensive analysis of y#{246} T cell subset composition during a viral disease in humans has been obtained in several studies of HIV-infected individuals. Increases in relative and absolute numbers of y T cells in the peripheral blood have been described in HIV-1-seropositive persons including those free of clinical infections caused by opportunistic pathogens [55-58]. These increases are often due to V#{246}Pcells and result in an inversion of the adult peripheral blood V2/V61 ratio
280
Journal
of
Leukocyte
T cells
suggested
Biology
Volume
58,
September
may
into
situation
type 6
immunodeficiency
been
tissues
Human herpesvirus type 6 (HHV-6), a T lymphotropic human herpesvirus, can infect y T cells isolated from peripheral blood [52]. Both #{128}43 and ‘y#{246} CD4 T cells are resistant to HIV infection. However, the HHV-6 infection of #{128}43 [53] or y [52] T cells induces transcription of CD4 mRNA, which is known to render human cells susceptible to HIV infection [54]. Indeed, the HHV-6--positive y#{246} T cells are infectable with human immunodeficiency virus (HIV) and this infection can be blocked by CD4 mAbs, confirming the CD4 requirement for the productive infection of ‘y#{246} T cells with HIV [52]. PHAand IL-2-stimulated y6 T cells isolated from healthy donors have been shown to lyse effectively autologous or heterologous HHV-6-infected PBMCs but not uninfected PBMCs. When the effector y T cells themselves were infected with HHV-6, their anti-HHV-6 cytotoxic capacity was only minimally affected during the first 72 h after infection. However, a substantial loss of cytotoxic activity was detected 4 days after the infection of y#{246} T cell effectors, at which time active viral replication was present.
Human
has
v1
that
the
be a result
circulation
peripheral
of cell under
expansion
trafficking
the
1995
in
blood,
increases
in
the
of
from
influence
changes occurring during HIV infection In contrast to V1 cells, the influence on the relative and absolute representation in the peripheral blood is less consistent, increases have been noted [55, 60-62].
molecules.
herpesvirus
In
of
the
various cytokine
[62]. of HIV infection of V#{246}2cells although some Similar to the
percentage
of
‘y
T
cells have been noted in the BAL lymphocyte population of some HIV-infected individuals, including those without clinical opportunistic infections [63]. These patients presented with the characteristic inversion of the peripheral blood V#{246}2/V#{246}l ratio, but the elevation in BAL y#{246} T cells was
found
to be
due
predominantly
to an
increase
in V#{246}2
T cells, which coexpressed various activation/adhesion molecules [63]. The percentage of peripheral yS T cells that express V’y2, 3, 4 is slightly greater in HIV-infected individuals than
in
uninfected
controls.
Approximately
50%
of
V#{246}1
cells from HIV-infected individuals coexpress either the V-y2, Vy3, or Vy4 chains (as assessed by reactivity with mAb 23D12), whereas this population represents about 30% of V1 cells in controls [62]. Because of a notable presence of cells that are not reactive with any of the currently
speculated HIV-infected [61, 62]. Infections rus
(SIV)
tope [16] Malkovsky,
available
that
y chain-specific
a substantial individuals
with induce
HIV-1 cell
mAbs,
percentage may express or
surface
simian
it
has
been
of y#{246} T cells from Vy5 or V’y8 chains immunodeficiency
expression
of
an
vi-
Hsp6O
epi-
Wallace, Ivanyi, Welch, Garcia, for publication) and increased cxpression of CD48 (also known as Blast-i or TCT.1) [i6, 64]. As these molecules have been associated with target cell recognition by cytotoxic y6 T lymphocytes [42-44, 65, 66],
been
the
(Bartz, submitted
T cell
lytic
activity
for
HIV-infected
targets
has
analyzed. It has been observed that human and simian y T cell clones and lines isolated from HIV-negative donors and Sly-negative rhesus monkeys, respectively, lysed in an MHC-unrestricted manner a variety of human HIV- or SIV-infected T cell lines much more efficiently than control uninfected cells [16, 64, 67]. Clonal analysis revealed that 12 of 30 (40%) V’y9/V2 T cell
clones,
but
none
peripheral
blood
of 7 V1
T cell
of healthy
clones
isolated
HIV-seronegative
from
the
donors,
dis-
played lytic activity against HIV-infected cells (Wallace, Bartz, Chang, MacKenzie, Pauza, Malkovsky, submitted for publication). Control #{128}43 T cell clones propagated in the same manner consistently failed to lyse HIV-infected cells. The V’y9/V2 T cell clones cytotoxic for HIV-infected cells typically lysed Daudi cells. However, not all V’y9/V#{246}2 T
cell
clones
that
lysed
Daudi
targets
had
the
capacity to lyse HIV-infected cells, indicating that the recognized ligands may be different on these two target cell types. The V’y chain of the TCR alone appears to be insufficient for the recognition of HIV-infected cells, as V’y9/Vi T cell clones did not lyse these targets. It has not been determined whether the cytotoxic response requires the expression of either the combination of V’y9 and V2 TCR segments or the V2 chain paired with any V’y chain. Clonal heterogeneity between different V’y9/V62 T cell clones may account for differences in the ability of vanous clones to recognize and lyse HIV-infected cells. The observation that 40% of these T cell clones lyse HIV-infected cells indicates that a substantial portion of the V’y9/V62
T
cell
population
may
have
the
capacity
to
re-
spond to HIV infection. The ligand recognized by these cells could be of either HIV origin or an HIV-induced host cell-derived component present in modified form or quantity on the surface of HIV-infected cells. It is possible that lysis of HIV-infected cells by Vy9/V#{246}2 T cells in vivo takes place early after host infection occurs, as it is appanent that these effector cells do not require previous activation by HIV-specific or induced antigens to mediate such
lysis.
Similarly,
V’y’/V2 T cell clones fected targets without [51]. These observations sis
that
y#{246} T cells
PHA-
or
have previous are
been shown to lyse HSV-inexposure to HSV antigens consistent with the hypothe-
may
mycobactenia-stimulated
function
early
in
disease
as
cells.
whether some of the in HIV-seropositive donors have lytic capacity toward
It
remains
to
vivo expanded proliferate HIV-infected
be
virus-infected
of nonpeptide antigens is not example, some #{128}43 T cells can recognize mycolic acid [68]-the responses of the major subpopulation of human peripheral blood ‘y#{246} T cells from putatively healthy adults (i.e., the V’y9/V2 T lymphocyte subset) to y-monoethyl derivatives of nucleoside and deoxynucleoside tniphosphates and prenyl pyrophosentirely
phates
cells. viral
[19]
are
doubt
that in many
y viral
T cell
determined
V8P T cells in response to cells.
responses
infections.
can The
unprecedented.
These
findings
rein-
responses or
could contribute pathogenesis.
In
to either the first
case, Hsps or alkyl phosphates may prove useful as vaccines, and in the latter case, the blocking of antigen-specific -l’6 T cell responses could be therapeutically beneficial. In either case, the y#{246} T cell activity in viral infections merits detailed and intensive studies.
in or
This work was supported by NIH grants RR-00167, Al33237, and AI-31972; American Cancer SocietyJFRA 399; a University of Pennsylvania Research Foundation Award; and the Tracy, Jamie and Dawn Ruhrup Memorial Fund. This is WRPRC publication 34-029.
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5.
any
quite
point that ‘y6 T cell specificity, and by function, is distinct from that of #{128}43 T cells. is not yet known if, or how, these structures to Hsp reactivity, the fact that prenyl pyroare derived from acetyl coenzyme A and arc of many lipophilic compounds could mdilinks in the recognition of virus-infected
These ‘y T cell immunosurveillance
Davis,
MM.,
be
results
from animal models of viral infections, in particular the influenza virus mouse model, suggest that y T cells act as part of an immune cell circuit (comprising #{128}43 T cells and macrophages) to regulate the initiation, progression, and perhaps the resolution of the viral immune response. The studies of y#{246} T cells in virus infections in humans suggest that their primary function may be to kill and eliminate virus-infected cells. However, not all ‘y T cells reactive with virus (HIV)-infected cells are cytotoxic, so there may also be populations of ‘y T cells involved in viral immune responses in humans that serve an immunoregulatory
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limited
ACKNOWLEDGMENTS
CONCLUSIONS It is beyond
the
force the implication Although it are related phosphates predecessors cate common
4.
cleanly
cells.
Although
front-
line defenders to remove infected or otherwise stressed cells. Some of the y#{246} T cell clones from HIV-seronegative donors were also investigated for potential proliferative responses to HIV-infected cells. One V’y9/V2 T cell clone and one V61#{247} T cell clone demonstrated proliferative responses toward HIV-infected cells but not uninfected cells. Another Vy9/V62 T cell clone proliferated in response to cell-free HIV in the presence or absence of antigen-presenting
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