Studies on cardiac myosin induced myocarditis

Abstract

Murine autoimmune myocarditis can be induced in genetically susceptible mice by immunization with cardiac myosin. Mice susceptible to autoimmune myocarditis develop a chronic inflammatory cell infiltrate and myocyte necrosis associated with the induction of heart-reactive antibodies and T cells.;In order to determine whether allelic polymorphisms in the alpha cardiac myosin heavy chain (myhca) contribute to the genetic basis for susceptibility to autoimmune myocarditis, I studied the immunogenicity and pathogenicity of two alleles of cardiac myosin in BALB/c and C57B/6 mice. These studies showed that BALB/c myosin which differs by 2 amino acids from C57B/6 myosin is significantly more pathogenic. Because the amino acid differences are in the S2 region of myosin, the data demonstrate that at least some pathogenic epitopes reside in that region. I confirmed this observation using genetically engineered fragments of rat myhca. This study leads to the suggestion that myosin genes may constitute part of a genetic susceptibility to autoimmune myocarditis.;I investigated the involvement of anti-myosin autoantibodies in the induction of autoimmune myocarditis. Myosin specific B cell hybridomas were generated from cardiac-myosin immunized A.CA, BALB/c and DBA/2 mice and purified monoclonal anti-myosin antibodies were injected into naive DBA/2 and BALB/c mice. Histopathologic analysis showed that IgG anti-myosin antibodies which recognize epitopes either on the head or rod of myhca induce myocarditis in DBA/2 mice but not in BALB/c mice. Immunohistochemical staining of mouse hearts showed that the deposition of antibody correlates with the presence of myocarditis. Furthermore, studies in SCID mice also showed an absence of deposition of antibody and antibody mediated disease in the hearts. These studies demonstrated that myocarditis in DBA/2 mice can be an antibody mediated disease. Electron micrographic studies suggested that the antibodies are deposited in the extracellular matrix and western blots of DBA/2 and BALB/c extracellular matrix proteins showed the presence of increased myosin in DBA/2 extracellular matrix preparations. These studies show that the susceptibility to autoimmune disease depends on end organ sensitivity to autoantibodies as well as on differences in the immune response.;I have also established conditionally immortalized cardiac myocyte cultures from the heart of adult H-2k{dollar}\sp{lcub}\rm b{rcub}{dollar}-tsA58 transgenic mice to be used in studies of antibody binding and extracellular matrix formation. These studies are included in an appendix.