SummaryThe zona pellucida (ZP), an ovarian extracellular structure, contains three major glycoproteins: ZP1, ZP2, and ZP3. A ZP3 peptide contains both an autoimmune oophoritis-inducing T cell epitope and a B cell epitope that induces autoantibody to ZP. This study investigates two major T cell costimulation pathways in this disease model. Herein we show that blockage of glycoprotein (gp)39 and CD40 interaction with gp39 monoclonal antibody (mAb) results in the failure to induce both autoimmune oophoritis and autoantibody production. Inhibition of hgand binding to the CD28 receptor with the fusion protein, murine CTLA4-immunoglobulin (Ig), also results in failure to generate antibody to ZP and significantly reduces disease severity and prevalence. Surprisingly, the frequencies of antigen-specific T cells in anti-gp39 mAbtreated mice, CTLA4-Ig treated mice, and in mice given control hamster IgG or control fusion protein L6, were equivalent as determined by hmiting dilution analysis (--~ 1 : 5,000). These T cells, which produced comparable amounts ofinterleukin 4 and interferon ~/in vitro, were able to transfer oophoritis to normal recipients. When anti-gp39 mAb and CTLA4-Ig were given together, the effect was additive, leading to inhibition of T cell activation as determined by in vitro prohferation and bruiting dilution analysis (-~1:190,000); disease and antibody responses were absent in these mice. By studying these two costimulatory pathways in parallel, we have shown that autoimmune disease and autoantibody production are inhibitable by blocking either the gp39 or the CD28 pathway, whereas inhibition of clonal expansion of the effector T cell population occurs only when both pathways are blocked.

Neonatal female mice injected with the self ZP3 peptide are not tolerant to the peptide; they develop autoimmune ovarian disease (AOD) and autoantibody response 5 weeks later. ZP3 challenge leads to severe AOD and ZP3-specific T cell and antibody responses. In contrast, neonatal tolerance to foreign ZP3 peptide is established in male mice: ZP3 peptide-specific T cell proliferative response is reduced and AOD is absent in ovarian grafts. Tolerance is associated with a Th2-dominant T cell cytokine and antibody isotype profiles. As controls, neonatal tolerance to foreign peptides, with Th2 deviation, was induced in both male and female mice. Endogenous ZP3 is important for the gender difference. Ablation of ovaries in female mice on days 2 and 5, but not on day 7 or 14, switches the ZP3 autoimmune response to a tolerogenic response with a concomitant change in cytokine profile. Thus, neonatal self ZP3 peptide, supported by endogenous ovaries within a neonatal time window, evokes a pathogenic autoimmune response.

Staphylococcal enterotoxin A (SEA), one of the most potent T-cell mitogens known, has been classified as a bacterial superantigen on the basis of ability to stimulate V beta-specific T-cell subsets. SEA interacts with class II major histocompatibility complex (MHC) antigens on antigen-presenting cells and the T-cell antigen receptor (TCR) on T cells, resulting in a ternary complex of MHC-SEA-TCR. Mls antigens are known to be products of mouse mammary tumour virus (MMTV), and it has been reported that two exogenous strains of MMTV encode retroviral superantigens in the open reading frames of the 3' long terminal repeat of the viral genome; however, no binding of the putative MMTV superantigen to either MHC antigens or TCR has been demonstrated. Here we use synthetic peptides to identify a site on the MMTV-1 superantigen that binds to class II MHC antigens. The site is encompassed by amino-acid residues 76-119 of the MMTV-1 superantigen. Direct binding and competition experiments show that the MMTV superantigen and SEA bind to at least one common region on class II MHC antigens.

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