Characterization of polymyositis infiltrates using monoclonal antibodies to human leucocyte antigens.

Frozen serial sections of muscle from 15 patients with polymyositis and three normal controls were studied by indirect immunofluorescence with a panel of mouse monoclonal antibodies to various human leucocyte components. The results showed good correlation with conventional histology. In addition, large numbers of T lymphocytes were identified in those cases with a marked inflammatory infiltrate. Many of the T cells probably bear HLA-DR antigen as the anti-HLA-DR antibody stained as many cells as the anti-leucocyte antiserum. This strongly suggests that the T cells present are 'activated'. In two patients HLA-DR-positive material was identified apparently diffusing from the infiltrates into muscle fibres suggesting its release as a soluble factor. In one case, structures with the appearance of giant cells were seen. The method promises to provide new information on the nature of infiltrating leucocytes which may provide more accurate diagnostic and prognostic information than conventional histology alone.