A comparative study of in vitro proliferative responses to mitogens and immunoglobulin production in patients with inflammatory muscle disease.

The classification of inflammatory muscle disorders is at best confusing owing to the wide spectrum of clinical, histological and serological findings within this group of patients. Although it is generally agreed that most cases reflect an autoimmune disorder with skeletal muscle as the primary target tissue, additional features of the more common form of the disease in juvenile patients, dermatomyositis, have suggested that it may differ in aetiology and pathogenesis from other forms of inflammatory muscle disease. Some adults may also be included within this category. In this study, we have divided patients with inflammatory muscle disease into two groups, 8 adult patients with 'pure' polymyositis and 13 children with dermatomyositis, and compared their in vitro lymphocyte function. Abnormal proliferative responses to T-cell mitogens were shown by peripheral blood mononuclear cells (PBM) from adult patients. PBM from the children gave values similar to normal control children. In vitro immunoglobulin production by cells from adult patients was comparable with appropriate controls both in the presence and absence of pokeweed mitogen. Childhood controls responded similarly to normal adults. PBM from the juvenile patients with dermatomyositis, however, produced significantly elevated levels of immunoglobulin spontaneously, with little or no increase for most patients following mitogen stimulation. This defective response was shown to be a consequence of activated T- and B-cells present in their peripheral blood and was not related to clinical parameters or drug therapy.