The expression of co-stimulatory and accessory molecules on cultured human muscle cells is not dependent on stimulus by pro-inflammatory cytokines: relevance for the pathogenesis of inflammatory myopathy.

Specific activation of naive T cells requires TCR engagement plus interaction of CD28 on T cells with co-stimulatory B7-1/B7-2 on APCs. Since muscle cells may be directly involved in activating muscle-infiltrating T lymphocytes in polymyositis and inclusion body myositis, we analyzed B7 expression on myoblasts before and after treatment with pro-inflammatory cytokines. We found no expression of B7-1/B7-2, either constitutively or after stimulus with cytokines. Furthermore, myoblasts failed to stimulate alloreactive peripheral blood lymphocytes in mixed lymphocyte reactions. Lack of B7 expression was confirmed by immunostaining of polymyositis patients' muscle: only T and the few B lymphocytes present in inflammation areas expressed B7-1.