Antibody-mediated autoimmune myocarditis depends on genetically determined target organ sensitivity.

Injury to cardiac myocytes often leads to the production of anti-myosin antibodies. While these antibodies are a marker of myocardial injury, their contribution to pathogenesis in diseases such as autoimmune myocarditis or rheumatic fever is much less clear. We demonstrate in this report that monoclonal anti-myosin antibodies can mediate myocarditis in a susceptible mouse strain. Additionally, we show disease susceptibility depends on the presence of myosin or a myosin-like molecule in cardiac extracellular matrix. This study demonstrates that susceptibility to autoimmune heart disease depends not only on the activation of self-reactive lymphocytes but also on genetically determined target organ sensitivity to autoantibodies.

Post-transcriptional regulation of rat alpha cardiac myosin heavy chain gene expression.

The cardiac myosin heavy chain genes, alpha and beta, have been shown to change their patterns of expression rapidly and dramatically in response to a variety of stimuli. A major means of achieving these changes in gene expression is transcriptional control; however, the role of post-transcriptional regulation in cardiac myosin gene expression has not been investigated. We have identified two post-transcriptional events in rat alpha cardiac myosin heavy chain (alpha-MHC) gene expression and investigated their regulatory significance in different developmental and thyroid hormone states. The polyadenylation of alpha-MHC mRNA occurs at three different sites: 12, 18, and 23 bases downstream from a single polyadenylation signal. Hyperthyroid hearts did not demonstrate any change in the proportion of the three alpha-MHC mRNA subspecies. Hypothyroid hearts (which have a decreased amount of total alpha-MHC mRNA) showed a significant increase in the proportion of the longest subspecies and a decrease in the shortest subspecies. The second post-transcriptional event in alpha-MHC gene expression which was demonstrated was the inclusion or exclusion of a codon, CAG, encoding glutamine at position 1931, resulting from alternate splicing of the alpha-MHC transcript. The ratio of CAG+ and CAG- forms of mRNA in the adult euthyroid hearts is 40:60% which was unchanged in hypo- and hyperthyroid states. This is the first example of alternate splicing in a vertebrate sarcomeric myosin heavy chain gene. We conclude that the rat alpha-MHC gene transcript is post-transcriptionally modified.

Cardiac alpha-myosin heavy chains differ in their induction of myocarditis. Identification of pathogenic epitopes.

BALB/c mice develop autoimmune myocarditis after immunization with mouse cardiac myosin, whereas C57B/6 mice do not. To define the immunogenicity and pathogenicity of cardiac myosin in BALB/c mice, we immunized mice with different forms of cardiac myosin. These studies demonstrate the discordance of immunogenicity and pathogenicity of myosin heavy chains. The cardiac alpha-myosin heavy chains of BALB/c and C57B/6 mice differ by two residues that are near the junction of the head and rod in the S2 fragment of myosin. Myosin preparations from both strains are immunogenic in susceptible BALB/c as well as in nonsusceptible C57B/6 mice; however, BALB/c myosin induces a greater incidence of disease. To further delineate epitopes of myosin heavy chain responsible for immunogenicity and disease, mice were immunized with fragments of genetically engineered rat alpha cardiac myosin. Epitopes in the region of difference between BALB/c and C57B/6 (residues 735-1032) induce disease in both susceptible and nonsusceptible mice. The data presented here demonstrate that pathogenic epitopes of both mouse and rat myosin residue in the polymorphic region of the S2 subunit. In addition, these studies suggest that polymorphisms in the autoantigen may be part of the genetic basis for autoimmune myocarditis.

Intermittent intravenous pulse cyclophosphamide treatment in systemic lupus erythematosus.

To determine the efficacy and safety of intermittent intravenous pulse cyclophosphamide in patients of severe systemic lupus erythematosus (SLE), 50 patients having severe/refractory lupus nephritis, vasculitis or neuropsychiatric manifestations were treated with 3 weekly pulses of cyclophosphamide for 6 such pulses. This treatment was found to be associated with significant and sustained improvement during a 2 yr follow up with respect to the mean renal activity score, individual renal parameters (proteinuria, erythrocyturia, and serum creatinine levels), focal neurological manifestations, vasculitic lesions, antinuclear antibody titers, complement component C3, anti-dsDNA antibodies levels and ESR. There was a sustained decrease in the overall mean disease activity score, and the mean daily dose of prednisolone (pretreatment 32.62 mg daily to 3.75 mg daily after 24 months). There was a significant decline in the percentage and absolute B cell count after 7, 14 and 21 days of this treatment. Effect on other lymphocyte subsets (CD3+, CD4+ and CD8+) was not marked. Pulse cyclophosphamide could therefore be an effective and less toxic form of treatment in patients with SLE having severe lupus nephritis, focal neurological lesions or vasculitis.

Effect of high dose intravenous pulse dexamethasone on lymphocyte phenotypes.

The lymphocyte phenotypes were enumerated in 10 patients with collagen diseases at 0 h, 4 h, 24 h and 7 days after a megadose (100 mg) iv pulse dexamethasone. A significant decrease in CD3 (from a mean of 2324.3/mm3 to 705.9/mm3) and CD4 (from a mean of 1642.6 to 317.6/mm3) cells was observed at 4 h, which recovered partially by 24 h (186.7 and 1226.3/mm3 respectively) and completely at 7 days (2496.1 and 1838.4/mm3). A transient decrease in CD8 cells at 4 h was also observed. There was no significant effect on B cells.