| Experimental autoimmune myocarditis (EAM) can be induced in A.SW mice by immunization with murine cardiac myosin in CFA. B10.S mice, which share the H2s haplotype, are resistant to EAM. We previously identified by linkage analysis a region on chromosome 1 that confers susceptibility to EAM (Eam1). The goal of this project is to identify genes within this locus that modify EAM and to discover a mechanism by which Eam1 regulates EAM susceptibility. To evaluate the role of Eam1, we created a congenic mouse strain, carrying the susceptible Eam1 locus of A.SW on the resistant B10.S background (B10.A- Eam1 congenic) and analyzed three outcomes: (1) the incidence and severity of EAM, (2) the expression and role of ICOS in EAM, (3) the susceptibility of lymph node cells (LNCs) to Cy-enhanced cell death, and (4) susceptibility of T cells and B cells to cell death following immunization with myosin/CFA. Incidence of myocarditis in B10.A-Eam1 congenic mice was comparable to A.SW mice. We identified ICOS as a likely candidate by gene expression and haplotype analysis. We discovered that the percentage of CD4 + T cells expressing ICOS was significantly decreased in the A.SW mouse than B10.S mice. However, the B10.A-Eam1 congenic mouse revealed an intermediate phenotype. Blocking ICOS during the priming phase of EAM in the A.SW mouse decreased EAM. We found that activation of caspases 3, 8 and 9 in LNCs following Cy treatment was significantly lower in A.SW than B10.S mice however, B10.A-Eam1 congenic mice showed an intermediate phenotype. Following immunization with myosin/CFA, CD4 + T cells with caspase 3, 8 and 9 activation was significantly lower in the A.SW mouse compared to B10.S while CD4+ lymphocytes of the B10.A-Eam1 congenic strain showed intermediate caspase activation. Our results show that Eam1 increases susceptibility to EAM and down regulates lymphocyte cell death through a caspase-dependent mechanism. In conclusion, allelic variations at the Eam1 susceptibility locus alters the susceptibility to cell death of CD4 + T cells and ICOS expression in response to myosin immunization and may provide an explanation of the mechanism as to how the Eam1 locus modulates EAM. |
