Corneal infection with herpes simplex virus type 1 leads to autoimmune responses in rats

Mapping of genes involved in murine herpes simplex virus keratitis: identification of genes and their modifiers

Herpes simplex keratitis (HSK) is an inflammatory response to viral infection and self antigens in the cornea and is a major cause of blindness. Using two strains of mice which are susceptible (129/SVEV) and resistant (C57BL/6) to herpes simplex virus (HSV) strain KOS, (129/SVEV x C57BL/6)F(2) mice were generated and examined for their disease susceptibility in terms of clinical symptoms, ocular disease, and antibody production following corneal scarification with HSV (KOS). A genome-wide screen was carried out using microsatellite markers to determine the genetic loci involved in this response. Loci on chromosomes 4, 5, 12, 13, and 14 were shown to be involved in general susceptibility to clinical disease, whereas loci on chromosomes 10 and 17 were shown to be unique to ocular disease.

Evidence for antigenic cross-reactivity between herpesvirus and the acetylcholine receptor

Herpes simplex virus (HSV) is neurotropic and can pass from neuron to neuron at nerve terminals. During the long evolutionary relationship between HSV and vertebrates, this virus may have evolved surface ligands that mimic nerve cell receptors. The present study was undertaken to determine if herpes simplex virus type 1 (HSV-1) has an antigenic relationship with the acetylcholine receptor (AChR). Mice immunized with HSV-1 antigens or an AChR-expressing cell line were tested for antibodies directed against the AChR. By flow cytometry and ELISA, mouse anti-HSV-1 sera were found to contain antibodies that would bind to an epitope on the plasma membrane of AChR-expressing cells. Mice immunized with the AChR-expressing cells were tested for their resistance to HSV-1 infection. Statistically significantly more of the animals immunized with AChR-expressing cells resisted infection and fatal encephalitis, compared to control animals immunized with a cell line not expressing the AChR. Sera from AChR-immunized mice were tested for anti-HSV antibody by ELISA and were found to contain antibodies cross-reactive with HSV-1 antigens. These sera also neutralized virus in a plaque inhibition assay. The results indicate that there are one or more antigenic epitopes shared by herpesvirus and the AChR. Studies are in progress to define the pathogenetic significance of this molecular mimicry.

Virus-Induced Immunoinflammatory Lesions in the Absence of Viral Antigen Recognition

Herpetic stromal keratitis (HSK) is a CD4+ T cell-controlled immunopathologic lesion in the eye that results from infection with herpes simplex virus (HSV). Target Ags involved in HSK remain undefined. In this study, we determined if HSK could be induced in animals genetically incapable of generating HSV Ag-specific CD4+ T cells. Mice bearing transgenic TCR specific to OVA peptide 323–339 (DO11.10) were crossed to SCID mice whose offspring (Tg-SCID) possessed CD4+ T cells, >98% of which expressed the OVA peptide-specific TCR. HSV infection of Tg-SCID mice was lethal, and mice failed to generate detectable T cell responses even after repeated immunization with a mutant avirulent virus (AN-1). Immunization with AN-1 virus followed by ocular challenge with HSV resulted in ocular inflammation before encephalitis, in contrast to the protection conferred in the control BALB/c and DO11.10 mice. These results indicate that clinical HSK may not require viral Ag recognition by CD4+ T cells and that T cells of irrelevant specificity can be recruited, activated, and driven into effector function in the HSV-infected cornea. This is suggested to represent a bystander activation effect resulting from the presence of proinflammatory mediators resulting from HSV replication.

The functional significance of epitope spreading and its regulation by co-stimulatory molecules

Epitope spreading is a process whereby epitopes distinct from and non-cross-reactive with an inducing epitope become major targets of an ongoing immune response. This phenomenon has been defined in experimental and natural situations as a consequence of acute or persistent infection and secondary to chronic tissue destruction that occurs during progressive autoimmune disease. We have investigated the functional significance of this process in the chronic stages of both autoimmune and virus-induced central nervous system (CNS) demyelinating disease models in the SJL/J mouse. During the relapsing-remitting course of experimental autoimmune encephalomyelitis (R-EAE) induced with defined encephalitogenic myelin peptides, CD4+ T cells specific for endogenous epitopes on both the initiating myelin protein (intramolecular epitope spreading) and distinct myelin proteins (intermolecular epitope spreading) are primed secondary to myelin destruction during acute disease and play a major functional role in mediating disease relapses. Similarly, epitope spreading to endogenous myelin epitopes appears to play a major functional role in the chronic-progressive course of Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD), a virus-induced CD4+ T-cell-mediated immunopathology. In TMEV-IDD, myelin destruction is initiated by virus-specific CD4+ T cells which target virus epitopes persisting in CNS-derived antigen-presenting cells. However, the chronic stage of this progressive disease is associated with the activation of CD4+ T cells specific for multiple myelin epitopes. In both models, the temporal course of T-cell activation occurs in a hierarchical order of epitope dominance, spreading first to the most immunodominant epitope and progressing to lesser immunodominant epitopes. In addition, epitope spreading in R-EAE is regulated predominantly by CD28/B7-1 co-stimulatory interactions, as antagonism of B7-1-mediated co-stimulation using anti-B7-1 F(ab) fragments is an effective ameliorative therapy for ongoing disease. The process of epitope spreading has obvious important implications for the design of antigen-specific therapies for the treatment of autoimmune disease since these therapies will have to identify and target endogenous self epitopes associated with chronic tissue destruction.

The interplay of T cell responses to viral and autoimmune epitopes

The examination of the immune T cell response to herpes simplex virus (HSV) antigen glycoprotein D (gD) in an ongoing infection has revealed a uniquely broad range of antigenic determinants seen. This has been shown in the murine T cell response to gD determinants where over 60% of the overlapping peptides are recognized as opposed to 1 of 30 peptides seen when gD was injected in Freund's adjuvant. This has also been seen in the response to local autoantigens when the HSV infection is produced by corneal scarification. Furthermore, analysis of the response to the autoantigen, Golli myelin basic protein (MBP), present in the developing thymus is explored.