Immune response to acute virus infection in the Syrian hamster. I. Studies on genetic restriction of cell-mediated cytotoxicity

Polymorphic peptide transporters in MHC class I monomorphic Syrian hamster

We have already shown that in species with highly polymorphic major histocompatibility complex (MHC) class I molecules (human, mouse) no functional polymorphism of the peptide transporters TAP1 and TAP2 is detectable (Lobigs and Müllbacher 1993). Investigating the antigen-presentation machinery of the class I MHC monomorphic Syrian hamster using mouse MHC class I expression via recombinant vaccinia viruses (VV) we found that six hamster cell lines fall into two phenotypic classes. four cell lines (HaK, FF, MF-2, and HT-1) showed no defect in expressing four different H2 class I molecules (Kk, Kd, Kb, Dd) and the appropriate VV peptide recognized by mouse VV-immune cytotoxic T (Tc) cells on the cell surface. Two cell lines (BHK-21 and NIL-2) expressed Dd and Kb in association with VV peptides as recognized by VV-immune, H2-restricted Tc cells but not Kk and Kd. However, Kd was expressed on the cell surface, as shown by fluorescence-activated cell sorter (FACS) analysis and alloreactive Tc-cell recognition. Kk is only surface-expressed in these two cell lines when superinfected with two VV recombinants encoding rat TAP1 (VV-mtp1) and TAP2 (VV-mtp2). Superinfection with VV-mtp1 and VV-mtp2 rendered both cell lines, after infection with either VV-Kk and VV-Kd, susceptible to lysis by either Kk- or Kd-restricted VV-immune Tc cells. Thus Syrian hamster cell lines express functionally polymorphic peptide transporters. The TAP2 gene from FF cells was cloned and sequenced; comparison with human, mouse, and rat TAP2 sequences show 78%, 88% and 87% similarity, respectively.

Poxvirus pathogenesis

Poxviruses are a highly successful family of pathogens, with variola virus, the causative agent of smallpox, being the most notable member. Poxviruses are unique among animal viruses in several respects. First, owing to the cytoplasmic site of virus replication, the virus encodes many enzymes required either for macromolecular precursor pool regulation or for biosynthetic processes. Second, these viruses have a very complex morphogenesis, which involves the de novo synthesis of virus-specific membranes and inclusion bodies. Third, and perhaps most surprising of all, the genomes of these viruses encode many proteins which interact with host processes at both the cellular and systemic levels. For example, a viral homolog of epidermal growth factor is active in vaccinia virus infections of cultured cells, rabbits, and mice. At least five virus proteins with homology to the serine protease inhibitor family have been identified and one, a 38-kDa protein encoded by cowpox virus, is thought to block a host pathway for generating a chemotactic substance. Finally, a protein which has homology with complement components interferes with the activation of the classical complement pathway. Poxviruses infect their hosts by all possible routes: through the skin by mechanical means (e.g., molluscum contagiosum infections of humans), via the respiratory tract (e.g., variola virus infections of humans), or by the oral route (e.g., ectromelia virus infection of the mouse). Poxvirus infections, in general, are acute, with no strong evidence for latent, persistent, or chronic infections. They can be localized or systemic. Ectromelia virus infection of the laboratory mouse can be systemic but inapparent with no mortality and little morbidity, or highly lethal with death in 10 days. On the other hand, molluscum contagiosum virus replicates only in the stratum spinosum of the human epidermis, with little or no involvement of the dermis, and does not spread systemically from the site of infection. The host response to infection is progressive and multifactorial. Early in the infection process, interferons, the alternative pathway of complement activation, inflammatory cells, and natural killer cells may contribute to slowing the spread of the infection. The cell-mediated response involving learned cytotoxic T lymphocytes and delayed-type hypersensitivity components appears to be the most important in recovery from infection. A significant role for specific antiviral antibody and antibody-dependent cell-mediated cytotoxicity has yet to be demonstrated in recovery from a primary infection, but these responses are thought to be important in preventing reinfection.

Delayed type-hypersensitivity response of inbred strains of Syrian golden hamsters (Mesocricetus auratus) to lethal or non-lethal lymphocytic choriomeningitis virus (LCMV) infections

In adult Syrian golden hamsters (Mesocricetus auratus), intraperitoneal or footpad inoculation of the lymphocytic choriomeningitis virus (LCMV) strains, WE or Armstrong (ARM), caused systemic infection and induced serum LCMV-antibody. Hamster and virus strain-dependent lethal disease also occurred. With WE, MHA and PD4 inbred hamsters failed to eliminate infection and died of wasting disease. LSH and CB inbred hamsters resisted lethal WE-disease and cleared infection. LVG hamsters and inbred LHC hamsters were intermediate in WE-susceptibility; some died of wasting, while others survived with little illness. Resistance to lethal WE-disease directly correlated with a delayed-type hypersensitivity (DTH) response to live-virus footpad inoculation. In WE-resistant LSH and CB hamsters, DTH-responses were induced by intraplantar WE-inoculation; footpad edema began by 5 days, reached maximum thickness by 7 to 9 days, and subsided thereafter. In the other hamster strains, DTH to WE could not be elicited. Unlike WE, ARM was hamster-avirulent; infections were self-limited and did not induce DTH. All survivors of primary LCMV (WE or ARM)-infection resisted secondary WE-challenge, and did not develop DTH to LCMV. Immunosuppressive treatments, abrogating DTH and antibody responses to LCMV, rendered all hamsters susceptible to lethal WE-infection. Hamster DTH most likely mediated resistance to virulent LCMV-infection.

Immunosuppression-induced susceptibility of inbred hamsters (Mesocricetus auratus) to lethal-disease by lymphocytic choriomeningitis virus infection

The role of the immune response in the pathogenesis of lethal and non-lethal lymphocytic choriomeningitis virus (LCMV)-infections of young adult Syrian golden hamsters (Mesocricetus auratus) of different strains was examined using immunosuppressive treatment with cyclophosphamide or with whole-body gamma-irradiation. In all hamsters, the LCMV strains, WE and Armstrong (ARM), caused systemic infections and induced comparable serum LCMV-antibody titers. However, lethal wasting-disease occurred which was hamster-strain and virus-strain dependent. With WE-inocula, MHA and PD4 inbred hamsters were all susceptible to lethal-disease and failed to completely eliminate infection. All LSH and CB inbred hamsters resisted lethal-disease and totally cleared WE-infection. Random colony-bred LVG hamsters and inbred LHC hamsters were intermediate in WE-susceptibility; some died with wasting, while others survived with minimal to no illness. ARM was avirulent for all hamsters and infections were totally cleared. By immunosuppressive treatment, all hamsters were rendered completely susceptible to lethal-disease by WE, and had unresolved infections and diminished serum LCMV-antibody titers. Immunosuppression also rendered all hamster strains partially susceptible to lethal infection by ARM. The hamster immune response was thus shown to suppress LCMV-infection and protect against lethal illness.

Cell-mediated cytotoxicity toward measles virus-infected target cells in randomly bred Syrian hamsters

Cell-mediated cytotoxicity (CMC) toward measles virus-infected cells was studied by a (51)Cr release assay with spleen cells from hamsters inoculated with measles virus (strain Lec) or control antigen and with spleen cells from normal hamsters. Spleen cells from measles virus-inoculated hamsters showed greater CMC toward infected than toward noninfected target cells (designated specific CMC). Specific CMC was maximal 7 days after virus inoculation and was declining by 9 to 10 days. Effector cells were present in a nonadherent cell population. Specific CMC was reduced after treatments of effector cells with antithymocyte serum plus complement. The decrease in cytotoxicity was greater toward infected target cells than toward noninfected target cells. Treatment of infected target cells with antimeasles serum did not increase specific CMC by effector cells from the majority of virus-inoculated hamsters. CMC toward infected target cells by normal spleen cells (natural killer cells) or spleen cells from hamsters inoculated with control antigen was approximately the same as, or more often less than, CMC toward noninfected target cells. Natural killer cells were present in a nonadherent cell population. Treatment of natural killer cells with antithymocyte serum plus complement caused a similar decrease in cytotoxicity toward both infected and noninfected target cells. This study demonstrated virus-specific cellular cytotoxicity of effector spleen cells from measles virus-inoculated hamsters. Although the data were compatible with T cells as the source of effector cells in the virus-specific CMC, definitive identification could not be made. Additional membrane markers for better characterization of hamster lymphocyte subpopulations are required.

The biochemical characterization of Syrian hamster cell-surface alloantigens. II. Immunochemical relationships between cell-surface alloantigens and class II MHC homologues

Immunochemical comparisons between hamster cell-surface p39/p29 alloantigens and putative MHC class I and II products indicate that p39/p29 alloantigens are probable class II products. Both p39/p29 alloantigens and class II homologues have varying expression in hamster lymphoid tissues and are absent from fibroblasts. In addition, analysis by nonequilibrium pH gradient electrophoresis demonstrates similar, although nonidentical, alloantigen and class II homologous charge profiles. This observation could reflect multiple class II subregions within the hamster MHC. These data therefore suggest an immunochemical description of the hamster MHC which is compatible with MHC models proposed for other mammalian species.

Hamster T cells participate in MHC alloimmune reactions but do not effect virus-induced cytotoxic activity

The participation of hamster T cells in a variety of putative MHC-determined reactions was studied utilizing a well-characterized, highly selective goat anti-hamster thymocyte (G alpha HT) serum. Hamster lymphoid cell suspensions treated with G alpha HT lose much of their capacity to induce local graft-versus-host reactions and to function as responder cells in mixed lymphocyte reactions. In contrast to the participation of hamster T cells in alloimmune reactions (MLR and GVHR), virus-induced, cytotoxic activity in hamsters undergoing acute virus infection is not T-cell-mediated. This latter finding was rather surprising in view of the major role played by cytotoxic T effector cells in comparably infected mice and rats. These results suggest that, although hamsters are able to respond to putative class II MHC disparities in allogeneic reactions, MHC-encoded molecules, presumably class I, are not utilized for induction of effective cytotoxic activity in response to acute virus infection in this species. The implications of these findings are discussed in relation to our present understanding of the hamster MHC.