Immune responses of DBA/2 mice bearing melanoma tumors: Cell-mediated immune responses after challenge with vaccinia virus

Summary Cell-mediated immune responses in DBA/2 mice bearing melanoma tumors (TB-mice) were measured and compared to similar responses in mice without tumors (C-mice). Splenic lymphocytes from TB-mice had a reduced capacity to respond to both B and T-cell mitogens, but TB-mice responded to infection with vaccinia virus by developing a virus-specific cytotoxic T-cell response equal to that measured with splenic effectors prepared from virus-infected C-mice. NK-cell activity, as measured by the in vitro lysis of YAC-1 targets by splenic effectors, was significantly depressed in TB-mice but, after infection of the animals with vaccinia virus, was restored to levels equal to that measured with splenic effectors prepared from C-mice. Doses of vaccinia virus, strain WR which elicited vaccinia-virus-specific cytotoxic T cells or stimulated NK-cell activity, failed to elicit or stimulate cytotoxic effectors specific for S91-melanoma tumor cells.     

A SYBR Green RT-PCR assay in single tube to detect human and bovine noroviruses and control for inhibition

Background

A subset of the virus-specific CD8+ cytotoxic T lymphocytes (CTL) isolated from the lungs of mice infected with human respiratory syncytial virus (RSV) is impaired in the ability to secrete interferon γ (IFNγ), a measure of functionality. It was suggested that the impairment specifically suppressed the host cellular immune response, a finding that could help explain the ability of RSV to re-infect throughout life.

Results

To determine whether this effect is dependent on the virus, the route of infection, or the type of infection (respiratory, disseminated, or localized dermal), we compared the CTL responses in mice following intranasal (IN) infection with RSV or influenza virus or IN or intradermal (ID) infection with vaccinia virus expressing an RSV CTL antigen. The impairment was observed in the lungs after IN infection with RSV, influenza or vaccinia virus, and after a localized ID infection with vaccinia virus. In contrast, we observed a much higher percentage of IFNγ secreting CD8+ lymphocytes in the spleens of infected mice in every case.

Conclusion

The decreased functionality of CD8+ CTL is specific to the lungs and is not dependent on the specific virus, viral antigen, or route of infection.     

A mouse model for immunization with ex vivo virus-infected dendritic cells

Dendritic cells (DCs) have been demonstrated to be an important if not essential inducer of cellular immune responses. The ability to grow these cells in vitro may open up new avenues for protective immunizations. In this study we have analyzed the virus-specific memory response generated following immunization with ex vivo-infected bone marrow-derived dendritic cells. We demonstrate that mouse DCs are efficiently infected with influenza virus but do not release infectious progeny virus. Ex vivo-infected DCs secrete interleukin-12 (IL-12) and induce a potent T helper (Th)1-like immune response when injected into mice. This was demonstrated by the generation of cytotoxic T lymphocytes, the production of high levels of gamma-interferon, and undetectable levels of IL-4 upon in vitro restimulation of splenocytes from immunized animals. In addition, the virus-specific antibody response is primarily of the IgG2a isotype, consistent with the expansion of Th1 cells. Animals immunized with DCs infected with X-31 influenza virus and challenged with PR8 influenza virus cleared the infection faster than animals not vaccinated. Thus, infected DCs efficiently activate the cellular immune response and induce heterosubtypic immunity in mice.     

Cell-mediated immunity to vesicular stomatitis virus infections in mice.

The T cell-mediated immune responses of mice against vesicular stomatitis virus (VSV) were assessed by measuring direct primary foot pad swelling after local VSV infection and cytotoxic activity in spleens. The cytolytic activity was mediated by T cells since it was anti-theta + complement sensitive, was restricted by the K and D region but not the I region of H-2 and rapidly increased after 4 days but decreased 8 days after systemic or local infection. Cytolytic activity was virus-specific as reciprocally tested with VSV and vaccina virus immune T cells. Measurable activity on day 7 depended on infectious virus dose, virus virulence, and non-H-2 genetic background of the host. More than half of the cytolytic activity wasblocked specifically by either immune anti-H2 or rabbit anti-VSV antisera. Analysis of the kinetics of appearance of antigenic changes using metabolic inhibitors, revealed that the changes that rendered target cells susceptible to lysis after infection, occurred within the first hour after infection.     

Local cellular defenses in influenza-infected lungs

The functional capacities and surface phenotype of the cells that accumulate in the lungs of hamsters during influenza A virus (PR/8/34) infection were studied to determine the cellular mechanisms that may limit the viral infection in the lung. Nonspecific natural killer (NK) cytotoxicity was augmented early (3 days) after infection in the lung but was undetectable at 6 days postinoculation. Virus-specific cytotoxic cells were detected within populations of mononuclear cells harvested from the lung but not from the hilar lymph node or spleen of influenza-infected hamsters following intratracheal inoculation. In contrast to virus-specific cytotoxic activity which remained locally, delayed-type hypersensitivity (DTH) activity was detected in assays in which cells were used from lung, hilar lymph nodes, or spleen. Depletion studies using rabbit anti-asialo GM1 and newly developed mouse monoclonals WI20 and WI38, which detect surface antigens on hamster T-lymphocyte populations, demonstrated that in the hamster NK cells are asialo GM+, WI20-, WI38-; DTH lymphocytes are asialo GM-, WI20+, WI38-; and cytotoxic T lymphocytes are asialo GM-, WI20+, WI38+. Together these data suggest that antigen-specific cytotoxic T cells can be induced locally within the hamster lung during influenza infection, but that they appear to be unable to circulate systemically, unlike the T cells that mediate DTH. Thus while the lung appears to share some immune responses to local infections with peripheral lymphoid organs, effector cells can be induced to develop locally and may be regulated locally without a mandatory involvement of the systemic immune system.     

Vaccinia virus-specific CD8+ cytotoxic T lymphocytes in humans.

Stimulation of human vaccinia virus immune peripheral blood mononuclear cells in vitro from vaccinia virus-immune donors with live vaccinia virus-infected autologous cells generated vaccinia virus-specific cytotoxic T lymphocytes (CTL) capable of lysing vaccinia virus-infected cells. We generated vaccinia virus-specific CD8+ clones and CD4+ CTL lines by limiting dilution from two donors by using peripheral blood mononuclear cells obtained 2 months or 4 years postrevaccination with vaccinia virus. These results demonstrate that vaccinia virus-specific CTL are generated as a result of immunization of humans with vaccinia virus and that both CD8(+)- and CD4(+)-specific T cells are maintained as memory cells.     

Anti-tumor immunity in adult T-cell leukemia

Adult T-cell leukemia (ATL) occurs in a small population of human T-cell leukemia virus type I (HTLV-I)-infected individuals. It has been noted that ATL is incidentally associated with mother-to-child infection which occurs mainly through breast-feeding, elevated levels of proviral load, and insufficiency in HTLV-I-specific cytotoxic T lymphocyte (CTL) responses. Among these, anti-tumor potentials of HTLV-I-specific CTL have been shown in ex vivo analysis of human HTLV-I-infected individuals and also in vivo experiments by using rat models of HTLV-I-infected lymphomas. In another rat model of HTLV-I-infection, orally infected rats showed significantly higher HTLV-I proviral load but lower HTLV-I-specific cellular immune responses than in intraperitoneally infected rats. As a result, persistent viral load was inversely correlated with levels of virus-specific T-cell responses. HTLV-I-specific T-cell responses in orally infected rats recovered by re-immunization. Conversion of Tax-specific T-cell responses from low to high levels was also observed in an ATL patient who obtained complete remission after hematopoietic stem cell transplantation. These findings suggest that HTLV-I-specific immune unresponsiveness associated with oral HTLV-I infection may be a potential risk factor for development of ATL, allowing expansion of the infected cell reservoir in vivo, and that immunological strategies targeting Tax may potentially reduce the risk of ATL and induce therapeutic effects on ATL.     

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.     

Epstein-Barr病毒特异性T细胞对重组痘苗病毒表达LMP和EBNA2的靶细胞的识别

本文用EB病毒转化自体淋巴细胞所建立的类淋巴母细胞系(LCL),以及用EB病毒潜伏感染膜蛋白(LMP)基因和核蛋白-2(EBNA2)基因与痘苗病毒重组的重组病毒(Vac-LMP和Vac-EBNA2)感染的自身纤维母细胞,同时作为刺激细胞和靶细胞,以~(51)Cr释放法检测5例血清中EB病毒VCA—IgA抗体阳性者及1例阴性健康者外周血单个核细胞(PBMC)的特异性T细胞杀伤效应。结果表明,用自身LCL激活的EB病毒特异性T细胞杀伤效应高峰出现在第14～28天;参与杀伤性细胞免疫反应的T细胞亚群主要是T3、T8阳性的细胞毒性T细胞,其对靶细胞的识别及杀伤受HLA-I的限制。用重组牛痘病毒感染的纤维母细胞作靶细胞或刺激细胞,有1例供者可接受LMP,另1例可接受EBNA2的刺激,并对相应的靶细胞产生特异性T细胞杀伤反应,表明EB病毒-LMP和EBNA2可能既是EB病毒特异性T细胞的刺激抗原,又是其识别的靶抗原。     

Immune responses to Herpesvirus sylvilagus infection in cottontail rabbits

Immunologic changes produced by Herpesvirus sylvilagus infection of cottontail rabbits were investigated to evaluate this virus infection system as an animal model for EBV infection in humans. H. sylvilagus neutralizing antibodies appeared as early as 7 days after infection, peaked 2 to 4 wk postinfection and decreased to low levels by 8 to 10 wk postinfection. Complement-dependent antibodies mediating the protection of in vitro infection of monocytes and Con A-stimulated lymphoblasts with H. sylvilagus were observed as were complement-dependent cytotoxic antibodies against H. sylvilagus-infected cells. No cytolytic activity was present in sera taken either before or 3 days after infection; cytolysis was first observed 7 days after infection. The development of cytolytic antibodies appeared to be biphasic during an infection course of 12 to 16 wk. In vivo induction of a primary cytotoxic lymphocyte response to H. sylvilagus was also investigated. Splenic lymphocytes from infected animals lysed H. sylvilagus-infected skin fibroblasts; however, similar activity was not observed when PBMC or mesenteric lymph node lymphocytes were used as effector cells. H. sylvilagus-infected autologous skin fibroblasts were preferentially lysed as compared to heterologous skin fibroblasts. This virus-specific cytotoxic activity appeared 5 days postinfection and peaked 7 days postinfection. By 28 days postinfection, only low levels of cytotoxic activity were detected in spleen cells. Herpesvirus sylvilagus infection of cottontail rabbits provides an animal model for the study of lymphoproliferative disorders induced by herpesviruses.     

Initial lentivirus-host interactions within lymph nodes: a study of maedi-visna virus infection in sheep.

Reactive changes occurring within lymph nodes draining the subcutaneous site of acute infection with maedi-visna virus (MVV) were studied, and the appearance of infected cells correlated with the immune response. Cells infected with virus were detected in the node by cocultivation from day 4 postinfection (p.i.), with maximum numbers being seen between days 7 and 14, but even then infected cells were rare, with a maximum frequency of 23 50% tissue culture infective doses (TCID50) in 10(6) lymph node cells. At later times, infected cells were still detected, but their numbers fell to 1 to 2 TCID50 per 10(6) cells. Virus-specific CD8+ cytotoxic T-cell precursors (CTLp) were isolated from infected nodes from day 10 p.i. onwards, and T-cell proliferative responses to MVV were first detected on day 7 and consistently detected after day 18. Histological analysis showed a vigorous immune response in the node. There was a marked blast reaction in the T-cell-rich zones, which was greatest at the time when the number of virally infected cells was at its height. At this stage, large numbers of plasma cells were seen in the medullary cords, indicating that extensive T-cell-dependent B-cell activation was occurring in the T-cell-rich zones. Germinal centers were prominent shortly after the onset of the T-zone response and were still present at 40 days p.i. Phenotype studies of isolated lymph node cells failed to detect major changes in the proportion or phenotype of macrophages, CD1+ interdigitating cells, and CD4+ or CD8+ T cells despite the fact that CD8+ lymphoblasts form a major population leaving the node in efferent lymph. This suggests that there is a balanced increase in the number of all cell types in response to the virus within the node and selective migration of CD8+ lymphoblasts containing virus-specific CTLp from the node. Virus-specific immune responses are therefore present within the node when infectious virus isolation is maximal, but cellular immunity may act to control the level of infection from day 18 onwards.     

The 22,000-kilodalton protein of respiratory syncytial virus is a major target for Kd-restricted cytotoxic T lymphocytes from mice primed by infection.

Recombinant vaccinia viruses containing the 22-kilodalton protein (matrixlike or 22K protein) or phosphoprotein gene from respiratory syncytial virus were constructed. These recombinant viruses expressed proteins which were immunoprecipitated by appropriate respiratory syncytial virus antibodies and comigrated with authentic proteins produced by respiratory syncytial virus infection. The new recombinant viruses (and others previously described containing the attachment glycoprotein, fusion, or nucleoprotein genes of respiratory syncytial virus) were used to infect target cells for cultured polyclonal cytotoxic T lymphocytes generated from the spleens of BALB/c or DBA/2 mice primed by intranasal infection with respiratory syncytial virus. Respiratory syncytial virus-specific cytotoxic T lymphocytes (CTL) showed strong Kd (but not Dd)-restricted recognition of the 22K protein. As previously reported, the fusion protein and nucleoprotein were both seen by CTL, but recognition of these proteins was comparatively weak. There was no detectable recognition of other respiratory syncytial virus proteins tested (including phosphoprotein). 22K protein-specific splenic memory CTL persisted for at least 11 months after infection of BALB/c mice. Priming BALB/c mice with recombinant vaccinia virus containing the 22K protein gene induced respiratory syncytial virus-specific memory CTL at lower levels than that previously reported following infection with a similar recombinant containing the fusion protein gene. These data identify the 22K protein as a major target antigen for respiratory syncytial virus-specific CTL from H-2d mice primed by respiratory syncytial virus infection.     

Expansion of human T-cell leukemia virus type 1 (HTLV-1) reservoir in orally infected rats: inverse correlation with HTLV-1-specific cellular immune response

Adult T-cell leukemia (ATL) occurs in a small population of human T-cell leukemia virus type 1 (HTLV-1)-infected individuals. Although the critical risk factor for ATL development is not clear, it has been noted that ATL is incidentally associated with mother-to-child infection, elevated proviral loads, and weakness in HTLV-1-specific T-cell immune responses. In the present study, using a rat system, we investigated the relationships among the following conditions: primary HTLV-1 infection, a persistent HTLV-1 load, and host HTLV-1-specific immunity. We found that the persistent HTLV-1 load in orally infected rats was significantly greater than that in intraperitoneally infected rats. Even after inoculation with only 50 infected cells, a persistent viral load built up to considerable levels in some orally infected rats but not in intraperitoneally infected rats. In contrast, HTLV-1-specific cellular immune responses were markedly impaired in orally infected rats. As a result, a persistent viral load was inversely correlated with levels of virus-specific T-cell responses in these rats. Otherwise very weak HTLV-1-specific cellular immune responses in orally infected rats were markedly augmented after subcutaneous reimmunization with infected syngeneic rat cells. These findings suggest that HTLV-1-specific immune unresponsiveness associated with oral HTLV-1 infection may be a potential risk factor for development of ATL, allowing expansion of the infected cell reservoir in vivo, but could be overcome with immunological strategies.     

Major histocompatibility complex-restricted CD8+ cytotoxic T lymphocytes from horses with equine infectious anemia virus recognize Env and Gag/PR proteins.

Cytotoxic T lymphocytes (CTL) can control some viral infections and may be important in the control of lentiviruses, including human immunodeficiency virus type 1. Since there is limited evidence for an in vivo role of CTL in control of lentiviruses, dissection of immune mechanisms in animal lentiviral infections may provide needed information. Horses infected with equine infectious anemia virus (EIAV) a lentivirus, have acute plasma viremia which is terminated in immunocompetent horses. Viremic episodes may recur, but most horses ultimately control infection and become asymptomatic carriers. To begin dissection of the immune mechanisms involved in EIAV control, peripheral blood mononuclear cells (PBMC) from infected horses were evaluated for CTL to EIAV-infected cells. By using noninfected and EIAV-infected autologous equine kidney (EK) cells in 51Cr-release assays, EIAV-specific cytotoxic activity was detected in unstimulated PBMC from three infected horses. The EIAV-specific cytotoxic activity was major histocompatibility complex (MHC) restricted, as determined by assaying EIAV-infected heterologous EK targets, and was mediated by CD8+ T lymphocytes, as determined by depleting these cells by a panning procedure with an anti-CD8 monoclonal antibody. MHC-restricted CD8+ CTL in unstimulated PBMC from infected horses caused significant specific lysis of autologous EK cells infected with recombinant vaccinia viruses expressing EIAV genes, either env or gag plus 5' pol. The EIAV-specific MHC-restricted CD8+ CTL were detected in two EIAV-infected horses within a few days after plasma viremia occurred and were present after viremia was terminated. The detection of these immune effector cells in EIAV-infected horses permits further studies to determine their in vivo role.     

Dengue virus-specific cross-reactive CD8+ human cytotoxic T lymphocytes

Stimulation with live dengue virus of peripheral blood mononuclear cells from a dengue virus type 4-immune donor generated virus-specific, serotype-cross-reactive, CD8+, class I-restricted cytotoxic T lymphocytes (CTL) capable of lysing dengue virus-infected cells and cells pulsed with dengue virus antigens of all four serotypes. These CTL lysed autologous fibroblasts infected with vaccinia virus-dengue virus recombinant viruses containing the E gene or several nonstructural dengue virus type 4 genes. These results demonstrate that both dengue virus structural and nonstructural proteins are targets for the cytotoxic T-cell-mediated immune response to dengue virus and suggest that serotype-cross-reactive CD8+ CTL may be important mediators of viral clearance and of virus-induced immunopathology during secondary dengue virus infections.     

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     

Generation of memory cell-mediated immune responses after secondary infection of mice with pichinde virus

Pichinde virus (PV), a member of the arenavirus group, was found to elicit strong cell-mediated immune responses in various strains of mice. After primary i.v. inoculation, augmentation of natural killer (NK) cell activity occurred and peaked 3 to 4 days after infection. The NK response was followed by a second peak of cytotoxic activity that was found to be H-2 restricted, virus specific, and mediated by Thy-1.2+, Lyt-2.2+ lymphocytes. This cytotoxic T lymphocyte (CTL) response peaked 7 days post infection. Neutralizing antibodies were not detectable after PV infection of the mice. In light of this, we investigated the generation and kinetics of secondary cell-mediated immune responses after reinjection of homologous virus in vivo. Slight but significant augmentation of NK activity was observed 1 day after secondary virus challenge. As in the primary response, effectors of this NK activity rapidly became sensitive to anti-Thy-1.2 and complement treatment. NK activity rapidly returned to background levels and was followed by an anamnestic CTL response that peaked 4 days after reinjection of the virus. Thus, cell-mediated immune responses appeared more rapidly after secondary challenge in vivo, and the temporal relationship between NK and CTL generation was maintained. Both secondary NK and CTL responses were generated in mice that had been pretreated with cyclophosphamide (CY), suggesting that memory cell-mediated immune responses can be reactivated in vivo without undergoing cell division. In contrast, treatment with CY before primary infection delayed the appearance of virus-induced NK activity and abrogated the generation of H-2-restricted virus-specific CTL. Rechallenge of these CY-treated NK-primed mice resulted in the rapid generation of a secondary NK response that was not followed by either a primary or secondary CTL response. The data suggest that cells mediating a nonspecific effector function may possess specific memory. We discuss our results with respect to possible NK-CTL relationships.     

Alveolar macrophages regulate the induction of primary cytotoxic T-lymphocyte responses during influenza virus infection.

Virus-specific cytotoxic T lymphocytes (CTL) are thought to be responsible for the eradication of respiratory influenza virus infections by direct cytolysis of virus-infected epithelial cells. In this study, we provide evidence for a role for alveolar macrophages (AM) in the regulation of pulmonary virus-specific CTL responses. Prior to infection with influenza virus, AM were selectively eliminated in vivo with a liposome-mediated depletion technique, and virus-specific CTL activities of lung and mediastinal lymph node (MLN) cells were assayed ex vivo and compared with those for normal mice. AM depletion resulted in increased primary CTL responses and changed the kinetics of the CTL response. Flow cytometric analysis of lung and MLN cells showed that the percentage of CD8+ cells was not altered after AM depletion and that lung cells from AM-depleted mice had an increased capacity to lyse virus-infected cells. Upon restimulation in vitro, virus-specific CTL activity in lung cells of normal mice was similar to that in lung cells of AM-depleted mice. Furthermore, elimination of AM resulted in increased virus titers in the lung, but virus clearance as a function of time was not affected. Our results show that AM regulate virus-specific CTL responses during respiratory influenza virus infection by removing viral particles, by downregulating the priming and activity of CTL in MLN cells, and by inhibiting the expansion of virus-specific CTL in the lung.     

Gamma interferon is not required for mucosal cytotoxic T-lymphocyte responses or heterosubtypic immunity to influenza A virus infection in mice

Heterosubtypic immunity (HSI) is defined as cross-protection against influenza virus of a different serotype than the virus initially encountered and is thought to be mediated by influenza virus-specific cytotoxic T lymphocytes (CTL). Since gamma interferon (IFN-gamma) stimulates cytotoxic cells, including antigen-specific CTL which may control virus replication by secretion of antiviral cytokines such as tumor necrosis factor alpha and IFN-gamma, we have investigated the mechanism of HSI by analyzing the role of IFN-gamma for HSI in IFN-gamma gene-deleted (IFN-gamma(-/-)) mice. It has been reported that IFN-gamma is not required for recovery from primary infection with influenza virus but is important for HSI. Here, we conclusively show that IFN-gamma is not required for induction of secondary influenza virus-specific CTL responses in mediastinal lymph nodes and HSI to lethal influenza A virus infection. Although T helper 2 (Th2)-type cytokines were upregulated in the lungs of IFN-gamma(-/-) mice after virus challenge, either Th1- or Th2-biased responses could provide heterosubtypic protection. Furthermore, titers of serum-neutralizing and cross-reactive antibodies to conserved nucleoprotein in IFN-gamma(-/-) mice did not differ significantly from those in immunocompetent mice. These results indicate that lack of IFN-gamma does not impair cross-reactive virus-specific immune responses and HSI to lethal infection with influenza virus. Our findings provide new insight for the mechanisms of HSI and should be valuable in the development of protective mucosal vaccines against variant virus strains, such as influenza and human immunodeficiency virus.     

Induction of feline immunodeficiency virus-specific cytotoxic T cells in vivo with carrier-free synthetic peptide.

The role of cellular immunity in the establishment and progression of immunosuppressive lentivirus infection remains equivocal. To develop a model system with which these aspects of the host immune response can be studied experimentally, we examined the response of cats to a hybrid peptide containing predicted T-and B-cell epitopes from the gag and env genes of feline immunodeficiency virus (FIV). Cats were immunized with an unmodified 17-residue peptide incorporating residues 196 to 208 (from gag capsid protein p24) and 395 to 398 (from env glycoprotein gp120) of the FIV Glasgow-8 strain by using Quil A as an adjuvant. Virus-specific lymphocytotoxicity was measured by chromium-51 release assays. The target cells were autologous or allogeneic skin fibroblasts either infected with recombinant FIV gag vaccinia virus or pulsed with FIV peptides. Effector cells were either fresh peripheral blood mononuclear cells or T-cell lines stimulated with FIV peptides in vitro. Cytotoxic effector cells from immunized cats lysed autologous, but not allogeneic, target cells when they were either infected with recombinant FIV gag vaccinia virus or pulsed with synthetic peptides comprising residues 196 to 205 or 200 to 208 plus 395. Depletion of CD8+ T cells, from the effector cell population abrogated the lymphocytotoxicity. Immunized cats developed an antibody response to the 17-residue peptide immunogen and to recombinant p24. However, no antibodies which recognized smaller constituent peptides could be detected. This response correlated with peptide-induced T-cell proliferation in vitro. This study demonstrates that cytotoxic T lymphocytes specific for FIV can be induced following immunization with an unmodified short synthetic peptide and defines a system in which the protective or pathological role of such responses can be examined.