Natural killer cells vs cytotoxic T cells in the peripheral blood of virus-infected mice

The cell-mediated immune response of mice against various enveloped RNA and DNA viruses expressed by immune lymphocytes from the spleen and the peripheral blood (PBL) were compared. PBL from mice of various strains infected with vaccinia virus, vesicular stomatitis virus (VSV), or lymphocytic choriomeningitis virus (LCMV) were tested on histocompatible or incompatible target cells infected with the homologous virus. PBL from immune mice showed clear H-2 restriction, but additionally, they expressed high natural killing (NK) activity on YAC-1 cells. The high NK-cytolytic activity of PBL on YAC-1 differed significantly from that expressed by splenic lymphocytes. In both lymphocyte populations lysis was detected as early as 1 day after infection; NK activity decreased in the spleen after day 4 post infection, whereas that of PBL persisted at high levels for up to 10 days after infection. Treatment of mice with anti-asialo GM1 in vivo abrogated NK activity in PBL effector cells tested in vitro. These results may explain some of the difficulties to observe MHC-restricted cytotoxic T cells in PBL from humans or primates during primary infections with virus.     

In vivo blockade of gamma interferon affects the influenza virus-induced humoral and the local cellular immune response in lung tissue.

Influenza virus infection induces the local production of gamma interferon (IFN-gamma) by T cells and non-T cells in the respiratory tract. To elucidate the possible functions of this cytokine, the humoral and local cellular immune responses to influenza virus were studied in BALB/c mice with or without in vivo neutralization of IFN-gamma by using monoclonal antibodies. Neutralization of IFN-gamma led to a significant reduction in virus-specific titers of immunoglobulins G2a and G3 in serum but had little effect on other isotypes. Studies on cells isolated from the lung parenchyma itself revealed that at the height of the immune response the ability of these cells to produce cytokines after antigen or T-cell receptor/CD3 stimulation was not affected. Ex vivo cytolytic activity by lung parenchyma cells, which is induced by infection with this virus in normal mice, was also found to be undisturbed by this treatment, even though anti-IFN-gamma antibody activity was recovered from lung lavage samples and sera at all days studied. Surprisingly, in vivo neutralization of IFN-gamma led to a significant reduction in the magnitude of the cellular infiltrate in the lung tissue which followed infection, suggesting an involvement of IFN-gamma in the mechanisms that regulate increased leucocyte traffic in the inflamed lung parenchyma. This conclusion was supported by findings of differences between mock-treated and anti-IFN-gamma-treated mice in the number of CD8+ lung T cells expressing CD49d (alpha4-integrin) and CD62L at various times after influenza virus infection. This study therefore demonstrates that IFN-gamma affects the local cellular response in the respiratory tract as well as the systemic humoral response to influenza virus infection.     

Persistence of vesicular stomatitis virus in cloned interleukin-2-dependent natural killer cell lines.

We have investigated virus-lymphocyte interactions by using cloned subpopulations of interleukin-2-dependent effector lymphocytes maintained in vitro. Cloned lines of H-2-restricted hapten- or virus-specific cytotoxic T lymphocytes (CTL) and alloantigen-specific CTL were resistant to productive infection by vesicular stomatitis virus (VSV). In contrast, cloned lines of natural killer (NK) cells were readily and persistently infected by VSV, a virus which is normally highly cytolytic. VSV-infected NK cells continued to proliferate, express viral surface antigen, and produce infectious virus. Furthermore, persistently infected NK cells showed no marked alteration of normal cellular morphology and continued to lyse NK-sensitive target cells albeit at a slightly but significantly reduced level. The persistence of VSV in NK cells did not appear to be caused by the generation of temperature-sensitive viral mutants, defective interfering particles, or interferon. Consequently, studies comparing the intracellular synthesis and maturation of VSV proteins in infected NK and mouse L cells were conducted. In contrast to L cells, in which host cell protein synthesis was essentially totally inhibited by infection, the infection of NK cells caused no marked diminution in the synthesis of host cell proteins. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of immunoprecipitates of viral proteins from infected cells showed that the maturation rate and size of VSV surface G glycoprotein were comparable in L cells and NK cells. Nucleocapsid (N) protein synthesis also appeared to be unaffected in NK cells. In contrast, the viral proteins NS and M appeared to be selectively degraded in NK cell extracts. Mixing experiments suggested that a protease in NK cells was responsible for the selective breakdown of VSV NS protein. Finally, VSV-infected NK cells were resistant to lysis by virus-specific CTL, suggesting that persistently infected NK cells may harbor virus and avoid cell-mediated immune destruction in an immunocompetent host.     

Persistent antigen presentation after acute vesicular stomatitis virus infection

Long-term antigen expression is believed to play an important role in modulation of T-cell responses to chronic virus infections. However, recent studies suggest that immune responses may occur late after apparently acute infections. We have now analyzed the CD8 T-cell response to vesicular stomatitis virus (VSV), which is thought to cause to an infection characterized by rapid virus clearance by innate and adaptive immune system components. Unexpectedly, virus-encoded antigen was detectable more than 6 weeks after intranasal VSV infection in both draining and nondraining lymph nodes by adoptively transferred CD8 T cells. Infection with Listeria monocytogenes expressing the same antigen did not result in prolonged antigen presentation. Weeks after VSV infection, discrete T-cell clustering with dendritic cells within the lymph node was observed after transfer of antigen-specific CD8 T cells. Moreover, memory CD8 T cells as defined by phenotype and function were generated from na?ve CD8 T cells entering the response late after infection. These findings suggested that protracted antigen presentation after an apparently acute virus infection may contribute to an ongoing antiviral immune response.     

Cardiac injury in myocarditis induced by Coxsackievirus group B, type 3 in Balb/c mice is mediated by Lyt 2 + cytolytic lymphocytes

Male Balb/c mice inoculated with a heart-adapted variant of Coxsackievirus, group B, type 3 (CVB3) develop severe myocarditis 7 days later. The lesions are characterized by mononuclear cell inflammation and myocyte necrosis. Infected T-lymphocyte-deficient mice show either minimal or no cardiac injury, although virus concentrations in the hearts of T-cell-deficient and -sufficient animals are similar. Adoptive transfer of 2 X 10(6) CVB3 immune Thy 1+ cells into CVB3-infected T-cell-deficient mice effectively restored myocarditis to levels observed in intact animals. Similar reconstitution with immune Ig+ cells or serum resulted in only a minimal increase in cardiac injury. To determine whether T-lymphocyte-dependent humoral or cellular immunity was responsible for myocarditis. T lymphocytes were obtained from Balb/c mice 6 days after infection with CVB3, separated into Lyt 1+2- (helper) and Lyt 1-2+ (cytolytic/suppressor) cell populations, and 2 X 10(6) of the enriched helper and cytolytic cells were adoptively transfused into infected T-cell-deficient recipients. Animals receiving the immune Lyt2+ cells developed severe myocarditis, had cytolytic T lymphocytes to both CVB3-infected and uninfected myocytes, but lacked a detectable IgG antibody response. Recipients of the Lyt 1+ cells failed to develop either myocarditis or cytolytic T cells but had normal serum IgG antibody titers to the virus. These results demonstrate that cardiac myocarditis is the product of cellular immune mechanisms.     

Cell-mediated immune response to lymphocytic choriomeningitis and vaccinia virus in rats.

The parameters of cell-mediated immune responses of rats to infection with lymphocytic choriomeningitis virus or vaccinia virus were assessed by measuring primary footpad swelling, increased weights of the local lymph nodes, increased numbers of lymphocytes per lymph node, and the course of virus-specific cytolytic activity by these lymphocytes. Except for lack of a defined swelling caused by vaccinia virus injected into the hind footpads of rats, the kinetics of all these responses correlated and were in accord with the usual time course of cellular immune responses. Starting 3 days after infection, peaking at 5 to 7 days, and disappearing after 10 to 12 days, the responses by rats to both viruses were comparable to those found in mice. The phagocytes of these infected rats inhibited the growth of Listeria monocytogenes in vivo, indicating activation of the macrophages by virus-specific cellular immunity. The rat cytotoxic lymphocytes were thymus derived as judged by various criteria: inactivation by an absorbed rabbit anti-rat brain antiserum plus C, susceptibility to anti Thy 1.1 plus C, restriction of the lytic activity within inbred strains and probably by the Ag-B locus, and the kinetics of the response. The cytotoxic T lymphocytes were virus specific since they killed only target cells infected with the same virus but not uninfected cells, or targets that were infected with an unrelated virus.     

Effect of vesicular stomatitis virus (VSV) infection on the development and regulation of T cell-mediated immune responses

Infection of mice with vesicular stomatitis virus (VSV) at the time of immunization failed to enhance T cell-mediated immune response to azobenzenearsonate-(ABA) conjugated spleen cells as measured by delayed-type hypersensitivity and by in vitro proliferation and in vitro generation of ABA-specific cytotoxic T cells. However, mice infected with VSV are incapable of responding to signals from suppressor T cells or their soluble factors. Further analysis revealed that VSV infection does not interfere with the induction of Ts-1 or Ts-2 cells. Because infection of Ts-1 or Ts-2 donors had no effect on the subsequent response seen in the recipients of antigen and suppressor T cells, the most likely candidate for the target of VSV infection is therefore the Ts-3 cell or another T cell interacting with Ts-3. This is supported by our observation that it is possible to bypass the VSV effect by providing the recipients of VSV with normal Lyt-2+-bearing T cells.     

Effects of treatment with IL-2 receptor specific monoclonal antibody in mice. Inhibition of cytotoxic T cell responses but not of T help

Contribution of IL-2R-bearing activated lymphocytes to antiviral host defense was investigated in C57BL/6 mice by treatment in vivo with IL-2R-specific mAb PC61. When treated on days 0 and 1 with respect to infection with either vaccinia virus, lymphocytic choriomeningitis (LCM) virus (LCMV) or vesicular stomatitis virus, 6-day immune mice had low numbers of CD8+ T cells that were reduced to about 10% of the values found for infected but otherwise untreated controls. In contrast, the number of CD4+ T cells was within normal ranges. Correspondingly, induction of strictly T help-dependent antiviral neutralizing IgG antibody titers remained unaffected by the mAb treatment, whereas generation of antiviral cytotoxic T cell activity was abrogated. Anti-IL-2R treatment of thymectomized mice 14 and 15 days after infection prevented generation of secondary antiviral cytotoxic T cells in restimulation cultures in vitro initiated 24 days later. Treatment with IL-2R-specific mAb was comparable to treatment with CD8-specific mAb in preventing mice to eliminate virus. Because of the involvement of antiviral cytotoxic T cells in disease manifestations, treatment with IL-2R-specific mAb protected mice from lethal LCM after intracerebral infection with LCMV and inhibited the footpad swelling reaction caused by local infection with the same virus.     

Adenovirus early region 1A modulation of interferon antiviral activity.

Human adenovirus type 5 (Ad5) is a DNA virus which replicates as efficiently in human A549 cells treated with human interferon-alpha 2 (IFN) as in untreated cells. Vesicular stomatitis virus (VSV), on the other hand, is a negative-strand RNA virus which is very sensitive to the effects of IFN treatment in A549 cells. The IFN-mediated inhibition of VSV replication was not observed in cells coinfected with Ad5. Abrogation of IFN-mediated antiviral activity was maximal when Ad5 infection preceded VSV infection by at least 36 h, but did not require adenovirus DNA synthesis for manifestation. Coinfection experiments with VSV and deletion variants of adenovirus demonstrated that neither virus-associated RNA synthesis nor expression of adenovirus early regions E1B, E2A, E3, or E4 are required for abrogation of IFN-mediated inhibition of VSV replication. However, expression of early region E1A was essential, suggesting that E1A products can modulate, either directly or indirectly, IFN activity in adenovirus-infected cells.     

Trojan horse lymphocytes: a vesicular stomatitis virus-specific T-cell clone lyses target cells by carrying virus

We have isolated a vesicular stomatitis virus (VSV)-specific CD4+ CD8- murine T-cell clone. This clone proliferates only in response to VSV and lyses infected tumor cells bearing class II major histocompatibility antigens in short-term chromium release assays. In addition, the cell has VSV antigens on its surface and is capable of killing uninfected tumor cells without major histocompatibility antigen restriction in a 2-day assay. This latter cytolytic activity is eliminated by anti-VSV antibody, indicating that its lytic activity is provided by the virus. [35S]methionine labeling and immunoprecipitation experiments demonstrated that viral protein translation is initiated after incubation of the clone with a tumor target cell, defining this as the mechanism of its cytolytic activity.     

Susceptibility of Friend virus antigen-modulated erythroleukemic cells to lysis by T lymphocytes from mice with dormant Friend virus infections.

Spleen cells from DBA/2 mice with dormant Friend leukemia virus (FLV) infections or from mice immunized with x-irradiated FLC-745 erythroleukemic cells are not cytolytic for FLC-745 cells when tested directly, but acquire cytolytic activity in vitro by cultivation with x-irradiated FLC-745 cells. Spleen cells cultured from normal mice do not acquire such cytolytic activity. Cytolytic activity resides in the T lymphocyte population. Alloantiserum, but not antisera against FLV-virion polypeptides, inhibited the lysis of FLC-745 cells by cytolytic T lymphocytes. To understand further the role of cellular and humoral immune anti-FLV responses in mice with dormant FLV-infections, in vitro experiments were conducted that mimicked the in vivo FLV-specific immune environment of these mice. We found that FLV-immune serum from mice with dormant FLV-infections modulated FLV-antigen expression on the surfaces of FLC-745 cells without affecting their susceptibility to lysis by cytolytic T lymphocytes. These results suggest that cytolytic T lymphocyte restrain the outgrowth of FLV-antigen-modulated erythroleukemic cells in mice with dormant FLV infections and that the targets for cell-mediated lysis may be H-2d-associated antigens.     

Immunobiology of infection with recombinant vaccinia virus encoding murine IL-2. Mechanisms of rapid viral clearance in immunocompetent mice.

CD8+ cytotoxic T (Tc) lymphocytes mediate recovery from vaccinia virus (VV) infection. In mice, anti-VV Tc cells are detectable on or after day 3 after infection, and cytolytic activity peaks between days 5 and 6. A rVV encoding murine IL-2, VV-hemagglutinin (HA)-IL-2, was cleared more rapidly, compared with a control rVV, VV-HA-thymidine kinase (TK), from tissues of infected euthymic normal mice. The mechanism of VV-HA-IL-2 clearance was operative early in infection and correlated with an elevated NK cell response, before the induction of anti-VV Tc cell response. We have investigated the roles of NK cells, T cells, and IFN-gamma in the rapid clearance of VV-HA-IL-2, by using specific mAb. Depletion of NK cells with mAb significantly enhanced VV-HA-IL-2 but not VV-HA-TK titers 3 days after infection. NK cells alone could not account for rapid viral clearance, because VV-HA-IL-2 titers in NK cell-depleted mice were not comparable to VV-HA-TK titers. Treatment with a mAb to IFN-gamma completely abrogated the IL-2-induced mechanism(s) of VV-HA-IL-2 clearance, and titers of the IL-2-encoding virus were comparable to control virus titers. In addition, the elimination of CD4+ but not CD8+ T cells resulted in significant increases in VV-HA-IL-2 titers.     

Replication-defective viruses modulate immune responses.

By immunizing inbred mice with purified replication-competent, defective virus particles, or an admixture of the two, differential effects on the cellular immune system have been uncovered. Defective virus, exemplified by the vesicular stomatitis virus (VSV) defective interfering particle (DI 0.33), induced in BALB/c mice low levels of proliferating, IL-2 secreting, and cytolytic Ag-specific T lymphocytes. This was not caused by a dominant suppressor cell response, or by a failure to stimulate lymphokine-secreting cells, but appeared to reflect a reduced efficiency of priming as compared with standard virus. Mice primed with a mixture of wt and DI virus showed reduced proliferation compared with mice primed with wt virus. When histocompatible target cells were sensitized by pure DI particles, they were neither recognized nor lysed by CD8+ CTL. Cells co-infected with wt and DI particles were not as readily lysed by CD8+ CTL as cells infected by VSV alone. The extent of this reduction was dependent on the concentration of DI particles. This suggests that DI particles may have prevented the proper presentation of endogenously synthesized Ag for recognition by CD8+ CTL. Metabolic labeling studies indicated that the presence of DI particles suppressed the synthesis of viral proteins in dually infected cells. However, CD4+ T lymphocyte clones recognized and efficiently lysed histocompatible Ia+ cells infected with DI particles alone or co-infected with replication-competent and defective virus.     

Interactions of vesicular stomatitis virus with murine cell surface antigens.

The process of maturation of vesicular stomatitis virus (VSV) results in the loss of 70% of the H-2k antigenic activity from L-cell plasma membranes. This phenomenon is also demonstrated during VSV infection of cells of the H-2d haplotype. Using the method of inhibition of immune cytolysis, VSV-infected L5178Y tissue culture cells and VSV-infected METH A fibrosarcoma cells grown in vivo show a loss of H-2d activity of 73 and 76%, respectively. Using monospecific antisera, it is seen that VSV infection results in a significant loss of antigenic activity of the gene products of both the H-2D and H-2K regions in cells of the H-2d and H-2k haplotypes. In hybrid cells expressing H-2k as well as H-2b, VSV infection results in the decrease of both H-2 antigenic activities to the same extent. VSV purified from L cells shows considerable H-2k activity, but the reaction of this virus with anti-H-2k serum does not prevent a normal subsequent infection with this virus. VSV may associate with H-2 antigen in the culture medium, but the results of mixing VSV with uninfected H-2-containing homogenates suggest that this association occurs only when the host cell and the cell homogenate share the same H-2 haplotype. Velocity sedimentation of VSV, which would remove contaminating cellular membrane fragments, does not separate H-2 activity from VSV. H-2 activity is also stably associated with VSV throughout sequential sucrose gradient centrifugation steps. It is possible that H-2 antigen is a structural component of VSV grown in murine cells.     

Cell-mediated immunologic responses and recurrent genital herpes in the guinea pig. Effects of glycoprotein immunotherapy.

The specific immune alterations associated with HSV recurrences are ill defined although it appears that alterations in cell-mediated immune mechanisms are more likely associated with recurrent disease than humoral immunity. Immunization with HSV glycoproteins B and D (gBgD) after primary HSV infection has reportedly reduced the frequency of recurrences but the mechanisms remain unidentified. We therefore evaluated the effects of immunization with cloned gBgD on selected cell-mediated immune responses and their relationship to recurrent disease by using the guinea pig model of genital HSV-2 infection. In two experiments, immunization with gBgD + CFA on days 21 and 42 after HSV-2 inoculation significantly decreased the number of subsequent recurrent lesion days observed whereas CFA alone had no effect. Immunization with gBgD + CFA increased the lymphoproliferative and in vitro IL-2 response to gBgD more than to whole HSV-2 Ag preparations. Peak responses were observed 2 wk after the second immunization. The HSV-specific cytolytic response was also persistently increased beginning 1 wk after the first immunization. Analysis including both untreated and gBgD-immunized animals revealed that recurrent lesion days were inversely correlated to the IL-2 response to whole HSV-2 Ag (p less than 0.0001), the IL-2 response to gBgD (p = 0.0004), and the HSV-specific cytolytic response (p = 0.005 and 0.003 in two experiments, respectively). When the untreated group was analyzed separately, only the IL-2 response to whole HSV-2 Ag correlated to recurrences (p = 0.007). HSV glycoprotein immunization may increase IL-2 or other cytokines secreted by HSV-sensitized T cells increasing critical immune responses, such as NK- or lymphokine-activated killer-mediated cytolysis, that could eliminate the reactivated virus before the development of clinically apparent lesions.     

Vesicular stomatitis virus oncolysis of T lymphocytes requires cell cycle entry and translation initiation

Vesicular stomatitis virus (VSV) is a candidate oncolytic virus that replicates and induces cell death in cancer cells while sparing normal cells. Although defects in the interferon antiviral response facilitate VSV oncolysis, other host factors, including translational and growth regulatory mechanisms, also appear to influence oncolytic virus activity. We previously demonstrated that VSV infection induces apoptosis in proliferating CD4(+) T lymphocytes from adult T-cell leukemia samples but not in resting T lymphocytes or primary chronic lymphocytic leukemia cells that remain arrested in G(0). Activation of primary CD4(+) T lymphocytes with anti-CD3/CD28 is sufficient to induce VSV replication and cell death in a manner dependent on activation of the MEK1/2, c-Jun NH(2)-terminal kinase, or phosphatidylinositol 3-kinase pathway but not p38. VSV replication is specifically impaired by the cell cycle inhibitor olomoucine or rapamycin, which induces early G(1) arrest, but not by aphidicolin or Taxol, which blocks at the G(1)1S or G(2)1M phase, respectively; this result suggests a requirement for cell cycle entry for efficient VSV replication. The relationship between increased protein translation following G(0)/G(1) transition and VSV permissiveness is highlighted by the absence of mTOR and/or eIF4E phosphorylation whenever VSV replication is impaired. Furthermore, VSV protein production in activated T cells is diminished by small interfering RNA-mediated eIF4E knockdown. These results demonstrate that VSV replication in primary T lymphocytes relies on cell cycle transition from the G(0) phase to the G(1) phase, which is characterized by a sharp increase in ribogenesis and protein synthesis.     

Virus-specific T-cell sensitization

Syngeneic, semiallogeneic, or allogeneic spleen lymphocytes were transferred intonu/nu BALB/c mice, which were infected with vaccinia virus. Specific Sensitization of transferred thymus-derived cells was determined in vivo by mean survival time and virus titer in the spleen six days after infection, and in vitro by cell-mediated cytolysis of vaccinia virus-infected syngeneic target cells. Virus-specific Sensitization took place only after transfer of syngeneic or semiallogeneic spleen lymphocytes; allogeneic lymphocytes had no influence on mean survival time or virus titer and showed no virus-specific cytolytic activity in vitro. Infection of mice with vaccinia virus-strain WR, Elstree, DIs, or DIs-infected syngeneic fibroblasts resulted in the generation of virus-specific effector cells, while injection of a high amount of inactivated virus particles caused no Sensitization. These results suggest H-2 homology for production of virus-specific effector cells. Propagation of virus is not necessary, since early surface antigens, combined with syngeneic H-2 antigens, suffice for Sensitization of cytolytic T lymphocytes.Abbreviations used in this paper are as follows CMC cell-mediated cytolysis - CTL cytolytic T lymphocyte - LCM lymphocytic choriomeningitis - MHC major histocompatibility complex - MST mean survival time - T cell thymus-derived cell - TCID₅₀ 50 percent tissue culture infective dose     

Effect of Vesicular Stomatitis Virus Infection on the Histocompatibility Antigen of L Cells

When mouse L cells are infected for 22 hr with vesicular stomatitis virus (VSV), a ribonucleic acid-containing enveloped virus, greater than 70% of the major histocompatibility antigen (H-2), is no longer detectable by the method of inhibition of immune cytolysis. Infected cells prelabeled with (14)C-glucosamine also show a correspondingly greater loss of trichloroacetic acid-insoluble radioactivity than uninfected cells. The loss of H-2 antigenic activity is not due to the viral inhibition of host cell protein synthesis since cells cultured for 18 hr in the presence of cycloheximide have the same amount of H-2 activity as untreated controls. Also, cells infected with encephalomyocarditis virus, a picornavirus, show no loss of H-2 activity at a time when host cell protein synthesis is completely inhibited. VSV structural proteins associated in vitro with uninfected L-cell plasma membranes do not render H-2 sites inaccessible to the assay. Although antibodies may not combine with all the H-2 antigenic sites on the plasma membrane, anti-H-2 serum reacted with L cells before infection does not prevent a normal infection with VSV. H-2 activity can be detected in virus samples purified from the medium of infected L cells; this virus purified after being mixed with L-cell homogenates shows greater H-2 activity than virus purified after being mixed with HeLa cell homogenates. However, VSV made in HeLa cells shows no H-2 activity when mixed with L-cell homogenates.     

Mechanism of recovery from acute virus infection: treatment of lymphocytic choriomeningitis virus-infected mice with monoclonal antibodies reveals that Lyt-2+ T lymphocytes mediate clearance of virus and regulate the antiviral antibody response.

After intravenous infection of mice, lymphocytic choriomeningitis virus multiplied in spleens and livers, attaining highest concentrations on days 4 to 6. The subsequent clearance was as rapid, and 8 to 10 days after inoculation, infectivity was usually below detectability. During the effector phase of virus elimination, both cytotoxic T-cell (CTL) activity and the number of cells producing antiviral antibodies were high. Monoclonal antibodies directed against T lymphocytes and T-lymphocyte subsets were inoculated once intravenously 5, 6, or 7 days after infection of the animals, and the effects on antiviral immune responses, as well as on elimination of virus from the organs, were determined. Treatment with anti-Thy-1 and anti-Lyt-2 antibodies blocked elimination of the virus and profoundly diminished the activity of spleen CTLs but reduced the antibody response partially (anti-Thy-1) or increased it (anti-Lyt-2). In contrast, treatment with the anti-L3T4 antibody had essentially no effect on either virus elimination or CTL response but abolished antibody production. We conclude that Lyt-2+ (cytotoxic-suppressive) T lymphocytes are needed for elimination of the virus and also regulate the humoral response but that antiviral antibodies are not essential for control of the infection.     

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.