The role of antibodies in natural and acquired resistance of mice to vesicular stomatitis virus

Mice infected with live vesicular stomatitis virus (VSV) produced primary antibody responses more efficiently (with doses greater than 10(2) pfu) than those injected with UV-inactivated VSV (greater than 10(6) pfu) or purified VSV glycoprotein G (equivalent to 10(7) pfu) by producing neutralizing antibodies. Very low doses of live VSV (less than 10(2) pfu) failed to prime mice. Normal mouse serum had the capacity to inactivate VSV by heat-labile and immunoglobulin-mediated mechanisms in vitro independently of specifically induced antibodies. Studies using B cell-depleted agammaglobulinaemic mice showed that their serum lacked VSV-neutralizing capacity in vitro and that naturally resistant mice became susceptible to VSV-induced paralytic disease which could be prevented by adoptive transfer of immune but also of normal serum.     

Immunosuppression in mice by lymphocytic choriomeningitis virus infection: time dependence during primary and absence of effects on secondary antibody responses

The kinetic study of immunosuppression caused by infection of mice with lymphocytic choriomeningitis virus WE (LCMV-WE) was assessed in DBA/2 (H-2d) and C57BL/6 (H-2b) mice. Infection with LCMV caused suppression of the Day 4 IgM response (complete in DBA/2 and incomplete in C57BL/6) and completely suppressed IgG responses on Days 9 and 42 to vesicular stomatitis virus (VSV) injected 2-11 days after LCMV. Suppression was partial when VSV was injected 16-28 days after LCMV-WE infection. The observed suppression between Day 2 and Day 11 was complete and nonspecific as revealed by the fact that these mice could not mount a secondary response to VSV when reinjected with the same VSV 42 days later. Nonspecificity of suppression was further indicated by the finding that the kinetics of recovery from suppression of the anti-VSV response were comparable for the VSV serotype used during the 2- to 11-day period after LCMV infection as for the serologically noncross-reactive second VSV serotype; both anti-VSV responses had recovered by Days 56-82 after LCMV infection. Once an anti-VSV antibody response was established, a subsequent LCMV-WE infection had no suppressive effect on Day 2 or Day 42 after a primary VSV infection. Also, the capacity of VSV-primed mice that were LCMV infected to respond to VSV in a secondary challenge infection with the same VSV was not impaired.     

Cytotoxic T cell activity is strain-specific in outbred mice infected with lymphocytic choriomeningitis virus.

The cytotoxic T cell response in outbred mice infected with lymphocytic choriomeningitis virus (LCMV) is strain specific. The same is true for adoptive transfer of fatal LCM disease. The response of individuals within an outbred strain is completely cross-reactive, as shown by using immune lymphocytes and virus-infected macrophage targets from individual mice. Reciprocal exclusion of cytotoxic T cell activity between inbred and outbred mouse strains is the rule, the exception being one strain (H) known to have some C57BL ancestry. Immune T cells from one of 7 H mice specifically lysed LCMV-infected C57BL macrophages. Experiments with inbred mice have shown that only one allele need be shared at either the H-2K or H-2D locus for cytotoxic T cell activity to be manifest. Adoptive transfer protocols may thus be considered in outbred situations, providing that T cells are effective before allograft rejection occurs. Also, the LCMV cytotoxic T cell assay may be useful for determining the degree of H-2 variability in wild mouse populations, as novel H-2 types can be detected and mice need not be congenic.     

Cellular Immune Recognition and the Biological Role of Major Transplantation Antigens

The experiments leading to the discovery of MHC-restricted T-cell killing of virus-infected cells are described. The implications of MHC- and HLA-restricted T-cell killing for the development of new vaccines and for the understanding of autoimmune disease are discussed.     

Cytotoxic T lymphocyte lysis of HTLV-1 infected cells is limited by weak HBZ protein expression,but non-specifically enhanced on induction of Tax expression

Background

Immunogenetic evidence indicates that cytotoxic T lymphocytes (CTLs) specific for the weak CTL antigen HBZ limit HTLV-1 proviral load in vivo, whereas there is no clear relationship between the proviral load and the frequency of CTLs specific for the immunodominant antigen Tax. In vivo, circulating HTLV-1-infected cells express HBZ mRNA in contrast, Tax expression is typically low or undetectable. To elucidate the virus-suppressing potential of CTLs targeting HBZ, we compared the ability of HBZ- and Tax-specific CTLs to lyse naturally-infected cells, by co-incubating HBZ- and Tax-specific CTL clones with primary CD4⁺ T cells from HLA-matched HTLV-1-infected donors. We quantified lysis of infected cells, and tested whether specific virus-induced host cell surface molecules determine the susceptibility of infected cells to CTL-mediated lysis.

Results

Primary infected cells upregulated HLA-A*02, ICAM-1, Fas and TRAIL-R1/2 in concert with Tax expression, forming efficient targets for both HTLV-1-specific CTLs and CTLs specific for an unrelated virus. We detected expression of HBZ mRNA (spliced isoform) in both Tax-expressing and non-expressing infected cells, and the HBZ_26–34 epitope was processed and presented by cells transfected with an HBZ expression plasmid. However, when coincubated with primary cells, a high-avidity HBZ-specific CTL clone killed significantly fewer infected cells than were killed by a Tax-specific CTL clone. Finally, incubation with Tax- or HBZ-specific CTLs resulted in a significant decrease in the frequency of cells expressing high levels of HLA-A*02.

Conclusions

HTLV-1 gene expression in primary CD4⁺ T cells non-specifically increases susceptibility to CTL lysis. Despite the presence of HBZ spliced-isoform mRNA, HBZ epitope presentation by primary cells is significantly less efficient than that of Tax.

     

Chemokine‐cleaving Streptococcus pyogenes protease SpyCEP is necessary and sufficient for bacterial dissemination within soft tissues and the respiratory tract

SpyCEP is a Streptococcus pyogenes protease that cleaves CXCL8/IL‐8 and its activity is associated with human invasive disease severity. We investigated the role of SpyCEP in S. pyogenes necrotizing fasciitis and respiratory tract infection in mice using isogenic strains differing only in SpyCEP expression. SpyCEP cleaved human CXCL1, 2, 6 and 8 plus murine CXCL1 and 2 at a structurally conserved site. Mice were infected in thigh muscle with a strain of S. pyogenes that expresses a high level of SpyCEP, or with an isogenic non‐SpyCEP expressing strain. SpyCEP expression by S. pyogenes hindered bacterial clearance from muscle, and enhanced bacterial spread, associated with cleavage of murine chemoattractant CXCL1. Mice were then infected with Lactococcus lactis strains that differed only in SpyCEP expression. In contrast to the parent L. lactis strain (lacks SpyCEP), which was avirulent when administered intramuscularly, infection with a strain that expressed SpyCEP heterologously led to dramatic systemic illness within 24 h, failure to clear bacteria from muscle and marked dissemination to other organs. In the upper airways, SpyCEP expression was required for survival of L. lactis but not S. pyogenes. However, dissemination of S. pyogenes to the lung was SpyCEP‐dependent and was associated with evidence of chemokine cleavage. Taken together, the studies provide clear evidence that SpyCEP is necessary and sufficient for systemic bacterial dissemination from a soft tissue focus in this model and also underlies dissemination in the respiratory tract.     

Aggravation of viral hepatitis by platelet-derived serotonin

More than 500 million people worldwide are persistently infected with hepatitis B virus or hepatitis C virus. Although both viruses are poorly cytopathic, persistence of either virus carries a risk of chronic liver inflammation, potentially resulting in liver steatosis, liver cirrhosis, end-stage liver failure or hepatocellular carcinoma. Virus-specific T cells are a major determinant of the outcome of hepatitis, as they contribute to the early control of chronic hepatitis viruses, but they also mediate immunopathology during persistent virus infection. We have analyzed the role of platelet-derived vasoactive serotonin during virus-induced CD8(+) T cell-dependent immunopathological hepatitis in mice infected with the noncytopathic lymphocytic choriomeningitis virus. After virus infection, platelets were recruited to the liver, and their activation correlated with severely reduced sinusoidal microcirculation, delayed virus elimination and increased immunopathological liver cell damage. Lack of platelet-derived serotonin in serotonin-deficient mice normalized hepatic microcirculatory dysfunction, accelerated virus clearance in the liver and reduced CD8(+) T cell-dependent liver cell damage. In keeping with these observations, serotonin treatment of infected mice delayed entry of activated CD8(+) T cells into the liver, delayed virus control and aggravated immunopathological hepatitis. Thus, vasoactive serotonin supports virus persistence in the liver and aggravates virus-induced immunopathology.     

Toll-like receptor engagement converts T-cell autoreactivity into overt autoimmune disease

Autoimmune diabetes mellitus in humans is characterized by immunological destruction of pancreatic beta islet cells. We investigated the circumstances under which CD8(+) T cells specific for pancreatic beta-islet antigens induce disease in mice expressing lymphocytic choriomeningitis virus (LCMV) glycoprotein (GP) as a transgene under the control of the rat insulin promoter. In contrast to infection with LCMV, immunization with LCMV-GP derived peptide did not induce autoimmune diabetes despite large numbers of autoreactive cytotoxic T cells. Only subsequent treatment with Toll-like receptor ligands elicited overt autoimmune disease. This difference was critically regulated by the peripheral target organ itself, which upregulated class I major histocompatibility complex (MHC) in response to systemic Toll-like receptor-triggered interferon-alpha production. These data identify the 'inflammatory status' of the target organ as a separate and limiting factor determining the development of autoimmune disease.