Gamma delta T cells facilitate adaptive immunity against West Nile virus infection in mice

West Nile (WN) virus causes fatal meningoencephalitis in laboratory mice, and gammadelta T cells are involved in the protective immune response against viral challenge. We have now examined whether gammadelta T cells contribute to the development of adaptive immune responses that help control WN virus infection. Approximately 15% of TCRdelta(-/-) mice survived primary infection with WN virus compared with 80-85% of the wild-type mice. These mice were more susceptible to secondary challenge with WN virus than the wild-type mice that survived primary challenge with the virus. Depletion of gammadelta T cells in wild-type mice that survived the primary infection, however, does not affect host susceptibility during secondary challenge with WN virus. Furthermore, gammadelta T cells do not influence the development of Ab responses during primary and at the early stages of secondary infection with WN virus. Adoptive transfer of CD8(+) T cells from wild-type mice that survived primary infection with WN virus to naive mice afforded partial protection from lethal infection. In contrast, transfer of CD8(+) T cells from TCRdelta(-/-) mice that survived primary challenge with WN virus failed to alter infection in naive mice. This difference in survival correlated with the numeric and functional reduction of CD8 memory T cells in these mice. These data demonstrate that gammadelta T cells directly link innate and adaptive immunity during WN virus infection.     

Gamma/delta T cell-deficient mice exhibit reduced disease severity and decreased inflammatory response in the brain in murine neurocysticercosis

In a recently developed mouse model for neurocysticercosis, the immune response was characterized by a massive influx of gammadelta T cells and a type 1 pathway of cytokine expression. To understand the role of gammadelta T cells during this infection, the cellular and cytokine response was analyzed in mice that lack gammadelta T cells (TCRdelta(-/-)). In TCRdelta(-/-) mice, Mesocestoides corti metacestodes preferentially invaded the extraparenchymal areas of the brain. Furthermore, parasites were able to escape from the brain and establish a systemic infection with liver and peritoneal involvement. Immunopathological studies indicated that TCRdelta(-/-) mice develop little inflammatory response and less neurological symptomatology. Significantly reduced numbers of T cells, macrophages, dendritic cells, and mast cells were present in the brain. The cytokine response in the brain of TCRdelta(-/-) mice appears to be a mixed type1/type 2 response with low levels of IL-2, IL-4, IL-10, IL-12, IL-13, IL-15, and IFN-gamma. To further investigate the immunological significance of this cell population, gammadelta T cells were adoptively transferred into intracranially infected TCRdelta(-/-) mice. gammadelta T cells were specifically recruited into the CNS in response to this parasitic infection, and they were able to target the infected brain within 12 h after transfer. These results suggest that gammadelta T cells are key players in the immune response elicited during this CNS infection and direct a type 1 response in wild-type mice upon infection.     

Protective immunosurveillance and therapeutic antitumor activity of gammadelta T cells demonstrated in a mouse model of prostate cancer

In contrast to Ag-specific alphabeta T cells, gammadelta T cells can kill malignantly transformed cells in a manner that does not require the recognition of tumor-specific Ags. Although such observations have contributed to the emerging view that gammadelta T cells provide protective innate immunosurveillance against certain malignancies, particularly those of epithelial origin, they also provide a rationale for developing novel clinical approaches to exploit the innate antitumor properties of gammadelta T cells for the treatment of cancer. Using TRAMP, a transgenic mouse model of prostate cancer, proof-of-concept studies were performed to first establish that gammadelta T cells can indeed provide protective immunosurveillance against spontaneously arising mouse prostate cancer. TRAMP mice, which predictably develop prostate adenocarcinoma, were backcrossed with gammadelta T cell-deficient mice (TCRdelta(-/-) mice) yielding TRAMP x TCRdelta(-/-) mice, a proportion of which developed more extensive disease compared with control TRAMP mice. By extension, these findings were then used as a rationale for developing an adoptive immunotherapy model for treating prostate cancer. Using TRAMP-C2 cells derived from TRAMP mice (C57BL/6 genetic background), disease was first established in otherwise healthy wild-type C57BL/6 mice. In models of localized and disseminated disease, tumor-bearing mice treated i.v. with supraphysiological numbers of syngeneic gammadelta T cells (C57BL/6-derived) developed measurably less disease compared with untreated mice. Disease-bearing mice treated i.v. with gammadelta T cells also displayed superior survival compared with untreated mice. These findings provide a biological rationale for clinical trials designed to adoptively transfer ex vivo expanded autologous gammadelta T cells for the treatment of prostate cancer.     

The interaction of gamma delta T cells with activated macrophages is a property of the V gamma 1 subset

Immunoregulation is an emerging paradigm of gammadelta T cell function. The mechanisms by which gammadelta T cells mediate this function, however, are not clear. Studies have identified a direct role for gammadelta T cells in resolving the host immune response to infection, by eliminating populations of activated macrophages. The aim of this study was to identify macrophage-reactive gammadelta T cells and establish the requirements/outcomes of macrophage-gammadelta T cell interactions during the immune response to the intracellular bacterium, Listeria monocytogenes (Lm). Using a macrophage-T cell coculture system in which peritoneal macrophages from naive or Lm-infected TCRdelta(-/-) mice were incubated with splenocytes from naive and Lm-infected alphabeta/gammadelta T cell-deficient and wild-type mice, the ability to bind macrophages was shown to be restricted to gammadelta T cells and the GV5S1 (Vgamma1) subset of gammadelta T cells. Macrophage adherence resulted in a 4- to 10-fold enrichment of Vgamma1(+) T cells. Enrichment of Vgamma1 T cells was dependent upon the activation status of macrophages, but independent of the activation status of gammadelta T cells. Vgamma1 T cells were cytotoxic for activated macrophages with both the binding to and killing of macrophages being TCR dependent because anti-TCRgammadelta Abs inhibited both Vgamma1 binding and killing activities. These studies establish the identity of macrophage cytotoxic gammadelta T cells, the conditions under which this interaction occurs, and the outcome of this interaction. These findings are concordant with the involvement of Vgamma1 T cells in macrophage homeostasis during the resolution of pathogen-mediated immune responses.     

Both gamma delta T cells and NK cells inhibit the engraftment of xenogeneic rat bone marrow cells and the induction of xenograft tolerance in mice

In murine allogeneic bone marrow transplantation recipients, treatment of the hosts with a nonmyeloablative regimen, including depleting anti-CD4 and anti-CD8 mAbs, allows establishment of long-term mixed chimerism and donor-specific tolerance. However, in the xenogeneic rat-to-mouse combination, additional anti-Thy1.2 and anti-NK1.1 mAbs are required. We have now attempted to identify the xenoresistant mouse cell populations that are targeted by anti-NK1.1 and anti-Thy1.2 mAbs. C57BL/6 (B6) wild-type, B6 TCRbeta(-/-), and B6 TCRdelta(-/-) mice received anti-CD4 and anti-CD8 mAbs, followed by 3 Gy of whole body irradiation, 7 Gy of thymic irradiation, and transplantation of T cell-depleted rat bone marrow cells. Anti-NK1.1 and anti-Thy1.2 mAbs were additionally administered to some groups. Increased rat chimerism was observed in TCRdelta(-/-) mice treated with anti-CD4, anti-CD8, and anti-NK1.1 mAbs compared with similarly treated TCRbeta(-/-) mice. In TCRbeta(-/-) mice, but not in TCR delta(-/-) mice, donor chimerism was increased by treatment with anti-Thy1.2 mAb, indicating that CD4(-)CD8(-)TCRgammadelta(+)Thy1. 2(+)NK1.1(-) cells (gammadelta T cells) are involved in the rejection of rat marrow. In addition, chimerism was enhanced in both TCRbeta(-/-) and TCRdelta(-/-) mice treated with anti-CD4, anti-CD8, and anti-Thy1.2 mAbs by the addition of anti-NK1.1 mAb to the conditioning regimen. Donor-specific skin graft prolongation was enhanced by anti-Thy1.2 and anti-NK1.1 mAbs in TCRdelta(-/-) mice. Therefore, in addition to CD4 and CD8 T cells, gammadelta T cells and NK cells play a role in resisting engraftment of rat marrow and the induction of xenograft tolerance in mice.     

Early expression of a functional TCRbeta chain inhibits TCRgamma gene rearrangements without altering the frequency of TCRgammadelta lineage cells

To investigate the consequences of the simultaneous expression in progenitor cells of a TCRgammadelta and a pre-TCR on alphabeta/gammadelta lineage commitment, we have forced expression of functionally rearranged TCRbeta, TCRgamma, and TCRdelta chains by means of transgenes. Mice transgenic for the three TCR chains contain numbers of gammadelta thymocytes comparable to those of mice transgenic for both TCRgamma and TCRdelta chains, and numbers of alphabeta thymocytes similar to those found in mice solely transgenic for a rearranged TCRbeta chain gene. gammadelta T cells from the triple transgenic mice express the transgenic TCRbeta chain, but do not express a TCRalpha chain, and, by a number of phenotypic and molecular parameters, appear to be bona fide gammadelta thymocytes. Our results reveal a remarkable degree of independence in the generation of alphabeta and gammadelta lineage cells from progenitor cells that, in theory, could simultaneously express a TCRgammadelta and a pre-TCR.     

A keratinocyte-responsive gamma delta TCR is necessary for dendritic epidermal T cell activation by damaged keratinocytes and maintenance in the epidermis

A unique population of T lymphocytes, designated dendritic epidermal T cells (DETC), homes to the murine epidermis during fetal development. DETC express a canonical gammadelta TCR, Vgamma3/Vdelta1, which recognizes Ag expressed on damaged, stressed, or transformed keratinocytes. Recently, DETC were shown to play a key role in the complex process of wound repair. To examine the role of the DETC TCR in DETC localization to the epidermis, maintenance in the skin, and activation in vivo, we analyzed DETC in the TCRdelta(-/-) mouse. Unlike previous reports in which the TCRdelta(-/-) skin was found to be devoid of any DETC, we discovered that TCRdelta(-/-) mice have alphabeta TCR-expressing DETC with a polyclonal Vbeta chain repertoire. The alphabeta DETC are not retained over the life of the animal, suggesting that the gammadelta TCR is critical for the maintenance of DETC in the skin. Although the alphabeta DETC can be activated in response to direct stimulation, they do not respond to keratinocyte damage. Our results suggest that a keratinocyte-responsive TCR is necessary for DETC activation in response to keratinocyte damage and for DETC maintenance in the epidermis.     

Innate immunity to viruses: control of vaccinia virus infection by gamma delta T cells

The existence of gammadelta T cells has been known for over 15 years, but their significance in innate immunity to virus infections has not been determined. We show here that gammadelta T cells are well suited to provide a rapid response to virus infection and demonstrate their role in innate resistance to vaccinia virus (VV) infection in both normal C57BL/6 and beta TCR knockout (KO) mice. VV-infected mice deficient in gammadelta T cells had significantly higher VV titers early postinfection (PI) and increased mortality when compared with control mice. There was a rapid and profound VV-induced increase in IFN-gamma-producing gammadelta T cells in the peritoneal cavity and spleen of VV-infected mice beginning as early as day 2 PI. This rapid response occurred in the absence of priming, as there was constitutively a significant frequency of VV-specific gammadelta T cells in the spleen in uninfected beta TCR KO mice, as demonstrated by limiting dilution assay. Also, like NK cells, another mediator of innate immunity to viruses, gammadelta T cells in uninfected beta TCR KO mice expressed constitutive cytolytic activity. This cytotoxicity was enhanced and included a broader range of targets after VV infection. VV-infected beta TCR KO mice cleared most of the virus by day 8 PI, the peak of the gammadelta T cell response, but thereafter the gammadelta T cell number declined and the virus recrudesced. Thus, gammadelta T cells can be mediators of innate immunity to viruses, having a significant impact on virus replication early in infection in the presence or absence of the adaptive immune response.     

Role of two distinct gammadelta T cell subsets during West Nile virus infection.

gammadelta T cells respond rapidly following West Nile virus (WNV) infection, limiting viremia and invasion of the central nervous system and thereby protecting the host from lethal encephalitis. Here, we investigated the role of two major subpopulations of peripheral gammadelta T cells, Vgamma1(+) and Vgamma4(+) cells, in host immunity against WNV infection. We found initially that aged mice were more susceptible to WNV infection than young mice. Following WNV challenge, Vgamma1(+) cells in young mice expanded significantly whereas Vgamma4(+) cells expanded modestly. In contrast, aged mice exhibited a slower and reduced response of Vgamma1(+) cells but maintained a higher content of Vgamma4(+) cells. Vgamma1(+) cells were the major gammadelta subset producing IFN-gamma during WNV infection. Mice depleted of Vgamma1(+) cells had an enhanced viremia and higher mortality to WNV encephalitis. Vgamma4(+) cells had a higher potential for producing tumor necrosis factor-alpha (TNF-alpha), a cytokine known to be involved in blood-brain barrier compromise and WNV entry into the brain. Depletion of Vgamma4(+) cells reduced TNF-alpha level in the periphery, accompanied by a decreased viral load in the brain and a lower mortality to WN encephalitis. These results suggest that Vgamma1(+) and Vgamma4(+) cells play distinct roles in protection and pathogenesis during WNV infection.     

gammadelta T cells may dichotomously modulate infection with avirulent Salmonella choleraesuis via IFN-gamma and IL-13 in mice

To investigate the roles of gammadelta T cells in Salmonella infection, we examined the resolution of an intraperitoneal infection with avirulent Salmonella choleraesuis 31N-1 in mice lacking T-cell-receptor (TCR) alphabeta T cells by disruption of the TCRbeta chain gene (TCRbeta(-/-)). The bacteria in TCRbeta(-/-) mice decreased with kinetics similar to that seen in control mice (TCRbeta(+/+)) after infection. The number of natural killer (NK) cells in the peritoneal cavity increased on day 6 after infection and thereafter decreased in both TCRbeta(-/-) and TCRbeta(+/+) mice, whereas the number of gammadelta T cells, in place of alphabeta T cells, increased remarkably in the peritoneal cavity of TCRbeta(-/-) mice on day 6 after infection. The NK cells from Salmonella-infected TCRbeta(-/-) mice produced interferon-gamma (IFN-gamma) but neither interleukin-4 (IL-4) nor IL-13 in response to immobilized anti-NK1.1 monoclonal antibody (mAb). The gammadelta T cells produced IFN-gamma but neither IL-4 nor IL-13 in response to heat-killed Salmonella, whereas both IFN-gamma and IL-13 but no IL-4 was produced by the gammadelta T cells stimulated with immobilized anti-TCRgammadelta mAb. In vivo administration of anti-NK1.1 mAb inhibited the reduction of Salmonella, whereas anti-TCRgammadelta mAb treatment did not affect the bacterial growth in TCRbeta(-/-) mice after Salmonella infection. However, neutralization of endogenous IL-13 with anti-IL-13 mAb enhanced the bacterial clearance in TCRbeta(-/-) mice after infection. These results suggest that NK1.1(+) cells serve mainly to protect against avirulent Salmonella infection in the absence of alphabeta T cells, whereas gammadelta T cells may play dichotomous roles in Salmonella infection through IFN-gamma and IL-13 in TCRbeta(-/-) mice.     

Tyk2-signaling plays an important role in host defense against Escherichia coli through IL-23-induced IL-17 production by gammadelta T cells

Tyrosine kinase 2 (Tyk2), a member of the JAK-signal transducer family, is involved in intracellular signaling triggered by various cytokines, including IL-23. We have recently reported that resident gammadelta T cells in the peritoneal cavity of naive mice produced IL-17 in response to IL-23. In this study, we examined importance of Tyk2-mediated signaling in the IL-17 production by gammadelta T cells using Tyk2 deficient (-/-) mice. Gammadelta T cells in the peritoneal cavity of Tyk2(-/-) mice displayed effecter/memory phenotypes and TCR V repertoire similar to those in Tyk2(+/+) mice and produced comparable level of IL-17 to those in Tyk2(+/+) mice in response to PMA and ionomycin, indicating normal differentiation to IL-17-producing effectors in the absence of Tyk2-signaling. However, gammadelta T cells in Tyk2(-/-) mice produced less amount of IL-17 in response to IL-23 in vitro than those in Tyk2(+/+) mice. Similarly, gammadelta T cells in the peritoneal cavity of Tyk2(-/-) mice showed severely impaired IL-17 production after an i.p. infection with E. coli despite comparable level of IL-23 production to Tyk2(+/+) mice. As a consequence, Tyk2(-/-) mice showed a reduced infiltration of neutrophils and severely impaired bacterial clearance after Escherichia coli infection. These results indicate that Tyk2-signaling is critical for IL-23-induced IL-17 production by gammadelta T cells, which is involved in the first line of host defense by controlling neutrophil-mediated immune responses.     

Gammadelta T cells promote a Th1 response during coxsackievirus B3 infection in vivo: role of Fas and Fas ligand

Fas/Fas ligand (FasL) interactions regulate disease outcome in coxsackievirus B3 (CVB3)-induced myocarditis. MRL(+/+) mice infected with CVB3 develop severe myocarditis, a dominant CD4(+) Th1 (gamma interferon [IFN-gamma(+)]) response to the virus, and a predominance of gammadelta T cells in the myocardial infiltrates. MRL lpr/lpr and MRL gld/gld mice, which lack normal expression of Fas and express a mutated FasL, respectively, have minimal myocarditis and show a dominant CD4(+) Th2 (interleukin-4 [IL-4(+)]) phenotype to CVB3. Spleen cells from virus-infected wild-type, lpr, and gld animals proliferate equally to virus in vitro. Adoptive transfer of gammadelta T cells from hearts of CVB3-infected MRL(+/+) mice (FasL(+)) into infected MRL gld/gld recipients (FasL(-)/Fas(+)) restores both disease susceptibility and Th1 cell phenotype. However, transfer of these cells into MRL lpr/lpr recipients (FasL(+)/Fas(-)) did not promote myocarditis and the viral response remained Th2 biased. This paralleled the expression of very high surface levels of FasL by myocardial gammadelta T cells, as well as their propensity to selectively lyse Th2 virus-specific CD4(+) T cells. These results demonstrate that Fas/FasL interactions conferred by gammadelta T cells on lymphocyte subpopulations may regulate the cytokine response to CVB3 infection and pathogenicity.     

Accumulation of gammadelta T cells in the lungs and their regulatory roles in Th1 response and host defense against pulmonary infection with Cryptococcus neoformans

The present study was designed to elucidate the role of gammadelta T cells in the host defense against pulmonary infection with Cryptococcus neoformans. The gammadelta T cells in lungs commenced to increase on day 1, reached a peak level on day 3 or 6, and then decreased on day 10 after intratracheal infection. The increase of these cells was similar in monocyte chemoattractant protein (MCP)-1-deficient mice, although that of NK and NKT cells was significantly reduced. The number of live microorganisms in lungs on days 14 and 21 was significantly reduced in mice depleted of gammadelta T cells by a specific mAb compared with mice treated with control IgG. Similarly, elimination of this fungal pathogen was promoted in gammadelta T cell-deficient (TCR-delta(-/-)) mice compared with control littermate mice. Finally, lung and serum levels of IFN-gamma on days 7 and 14 and on day 7 postinfection, respectively, were significantly higher in TCR-delta(-/-) mice than in littermate mice, whereas levels of TGF-beta showed the opposite results. IL-4 and IL-10 were not different between these mice. IFN-gamma production by draining lymph node cells upon restimulation with cryptococcal Ags was significantly higher in the infected TCR-delta(-/-) mice than in control mice. Our results demonstrated that gammadelta T cells accumulated in the lungs in a manner different from NK and NKT cells after cryptococcal infection and played a down-modulatory role in the development of Th1 response and host resistance against this fungal pathogen.     

Gamma interferon plays a crucial early antiviral role in protection against West Nile virus infection

West Nile virus (WNV) causes a severe central nervous system (CNS) infection in humans, primarily in the elderly and immunocompromised. Prior studies have established an essential protective role of several innate immune response elements, including alpha/beta interferon (IFN-alpha/beta), immunoglobulin M, gammadelta T cells, and complement against WNV infection. In this study, we demonstrate that a lack of IFN-gamma production or signaling results in increased vulnerability to lethal WNV infection by a subcutaneous route in mice, with a rise in mortality from 30% (wild-type mice) to 90% (IFN-gamma(-/-) or IFN-gammaR(-/-) mice) and a decrease in the average survival time. This survival pattern in IFN-gamma(-/-) and IFN-gammaR(-/-) mice correlated with higher viremia and greater viral replication in lymphoid tissues. The increase in peripheral infection led to early CNS seeding since infectious WNV was detected several days earlier in the brains and spinal cords of IFN-gamma(-/-) or IFN-gammaR(-/-) mice. Bone marrow reconstitution experiments showed that gammadelta T cells require IFN-gamma to limit dissemination by WNV. Moreover, treatment of primary dendritic cells with IFN-gamma reduced WNV production by 130-fold. Collectively, our experiments suggest that the dominant protective role of IFN-gamma against WNV is antiviral in nature, occurs in peripheral lymphoid tissues, and prevents viral dissemination to the CNS.     

V gamma 1+ T cells suppress and V gamma 4+ T cells promote susceptibility to coxsackievirus B3-induced myocarditis in mice

Coxsackievirus B3 infections of C57BL/6 mice, which express the MHC class II IA but not IE Ag, results in virus replication in the heart but minimal myocarditis. In contrast, Bl.Tg.Ealpha mice, which are C57BL/6 mice transgenically induced to express IE Ag, develop significant myocarditis upon Coxsackievirus B3 infection. Despite this difference in inflammatory damage, cardiac virus titers are similar between C57BL/6 and Bl.Tg.Ealpha mice. Removing gammadelta T cells from either strain by genetic manipulation (gammadelta knockout(ko)) changes the disease phenotype. C57BL/6 gammadelta ko mice show increased myocarditis. In contrast, Bl.Tg.Ealpha gammadelta ko mice show decreased cardiac inflammation. Flow cytometry revealed a difference in the gammadelta cell subsets in the two strains, with Vgamma1 dominating in C57BL/6 mice, and Vgamma4 predominating Bl.Tg.Ealpha mice. This suggests that these two Vgamma-defined subsets might have different functions. To test this possibility, we used mAb injection to deplete each subset. Mice depleted of Vgamma1 cells showed enhanced myocarditis, whereas those depleted of Vgamma4 cells suppressed myocarditis. Adoptively transfusing enriched Vgamma4(+) cells to the C57BL/6 and Bl.Tg. Ealpha gammadelta ko strains confirmed that the Vgamma4 subset promoted myocarditis. Th subset analysis suggests that Vgamma1(+) cells biased the CD4(+) T cells to a dominant Th2 cell response, whereas Vgamma4(+) cells biased CD4(+) T cells toward a dominant Th1 cell response.     

Characterization of TCR gene rearrangements during adult murine T cell development

Development of the alphabeta and gammadelta T cell lineages is dependent upon the rearrangement and expression of the TCRalpha and beta or gamma and delta genes, respectively. Although the timing and sequence of rearrangements of the TCRalpha and TCRbeta loci in adult murine thymic precursors has been characterized, no similar information is available for the TCRgamma and TCRdelta loci. In this report, we show that approximately half of the total TCRdelta alleles initiate rearrangements at the CD44highCD25+ stage, whereas the TCRbeta locus is mainly in germline configuration. In the subsequent CD44lowCD25+ stage, most TCRdelta alleles are fully recombined, whereas TCRbeta rearrangements are only complete on 10-30% of alleles. These results indicate that rearrangement at the TCRdelta locus can precede that of TCRbeta locus recombination by one developmental stage. In addition, we find a bias toward productive rearrangements of both TCRdelta and TCRgamma genes among CD44highCD25+ thymocytes, suggesting that functional gammadelta TCR complexes can be formed before the rearrangement of TCRbeta. These data support a model of lineage commitment in which sequential TCR gene rearrangements may influence alphabeta/gammadelta lineage decisions. Further, because TCR gene rearrangements are generally limited to T lineage cells, these analyses provide molecular evidence that irreversible commitment to the T lineage can occur as early as the CD44highCD25+ stage of development.     

gammadelta T cells contribute to control of chronic parasitemia in Plasmodium chabaudi infections in mice

During a primary infection of mice with Plasmodium chabaudi, gammadelta T cells are stimulated and their expansion coincides with recovery from the acute phase of infection in normal mice or with chronic infections in B cell-deficient mice (mu-MT). To determine whether the large gammadelta T cell pool observed in female B cell-deficient mice is responsible for controlling the chronic infection, studies were done using double-knockout mice deficient in both B and gammadelta cells (mu-MT x delta-/-TCR) and in gammadelta T cell-depleted mu-MT mice. In both types of gammadelta T cell-deficient mice, the early parasitemia following the peak of infection was exacerbated, and the chronic parasitemia was maintained at significantly higher levels in the absence of gammadelta T cells. The majority of gammadelta T cells in C57BL/6 and mu-MT mice responding to infection belonged predominantly to a single family of gammadelta T cells with TCR composed of Vgamma2Vdelta4 chains and which produced IFN-gamma rather than IL-4.     

Accumulation of gamma/delta T cells in the lungs and their roles in neutrophil-mediated host defense against pneumococcal infection

The present study was designed to elucidate the role of Vgamma4(+) gammadelta T cells, a major subset of pulmonary gammadelta T cells, in host defense against infection with Streptococcus pneumoniae. The proportion and number of whole gammadelta T cells, identified as CD3(+) and TCR-delta(+) cells, and Vgamma4(+) gammadelta T cells, identified as CD3(+) and TCR-Vgamma4(+) cells, increased in the lungs at 3, 6 and 12h post-infection. Survival of infected mice and lung bacterial clearance were severely impaired in TCR-Vgamma4(-/-) mice compared with control wild-type (WT) mice. The impaired host protection in TCR-Vgamma4(-/-) mice correlated well with attenuated recruitment of neutrophils in lungs. MIP-2 and TNF-alpha synthesis in the infected tissues was significantly reduced in TCR-Vgamma4(-/-) mice compared with WT mice. Similar results were noted in the synthesis of TNF-alpha, but not clearly of MIP-2, by lung leukocytes stimulated with live bacteria. Our results demonstrate that Vgamma4(+) gammadelta T cells play an important role in the neutrophil-mediated host defense against S. pneumoniae infection by promoting the synthesis of TNF-alpha and possibly of MIP-2 in the lungs.     

Deficiency of gammadelta T lymphocytes contributes to mortality and immunosuppression in sepsis

Studies have indicated that gammadelta T lymphocytes play an important role in the regulation of immune function and the clearance of intracellular pathogens. We have recently reported that intraepithelial lymphocytes (IEL), which are rich in gammadelta T cells, within the small intestine illustrated a significant increase in apoptosis and immune dysfunction in mice subjected to sepsis. However, the contribution of gammadelta T cells to the host response to polymicrobial sepsis remains unclear. In this study, we initially observed that after sepsis induced by cecal ligation and puncture (CLP), there was an increase in small intestinal IEL CD8+gammadelta+ T cells in control gammadelta+/+ mice. Importantly, we subsequently found an increased early mortality in mice lacking gammadelta T cells (gammadelta-/- mice) after sepsis. This was associated with decreases in plasma TNF-alpha, IL-6, and IL-12 levels in gammadelta-/- mice compared with gammadelta+/+ mice after sepsis. In addition, even though in vitro LPS-stimulated peritoneal macrophages showed a reduction in IL-6 and IL-12 release after CLP, these cytokines were less suppressed in macrophages isolated from gammadelta-/- mice. Alternatively, IL-10 release was not different between septic gammadelta+/+ and gammadelta-/- mice. Whereas T helper (Th)1 cytokine release by anti-CD3-stimulated splenocytes was significantly depressed in septic gammadelta+/+ mice, there was no such depression in gammadelta-/- mice. However, gammadelta T cell deficiency had no effect on Th2 cytokine release. These findings suggest that gammadelta T cells may play a critical role in regulating the host immune response and survival to sepsis, in part by alteration of the level of IEL CD8+gammadelta+ T cells and through the development of the Th1 response.     

Plasticity of immune responses suppressing parasitemia during acute Plasmodium chabaudi malaria.

gammadelta T cells have a crucial role in cell-mediated immunity (CMI) against P. chabaudi malaria, but delta-chain knockout (KO) (deltao/o) mice and mice depleted of gammadelta T cells with mAb cure this infection. To address the question of why mice deficient in gammadelta T cells resolve P. chabaudi infections, we immunized deltao/o mice by infection with viable blood-stage parasites. Sera from infection-immunized mice were tested for their ability to protect JHo/o, deltao/o double KO mice passively against P. chabaudi challenge infection. The onset of parasitemia was significantly delayed in mice receiving immune sera, compared with saline or uninfected serum controls. Immune sera were then fractionated into Ig-rich and Ig-depleted fractions by HPLC on a protein G column. Double KO mice were passively immunized with either fraction and challenged with P. chabaudi. The onset of parasitemia was significantly delayed in recipients of the Ig-rich fraction compared with recipients of the Ig-poor fraction of immune sera. We conclude that deltao/o mice, which are unable to activate CMI against the parasite, suppress P. chabaudi infection by a redundant Ab-mediated process.