Eosinophilia myalgia syndrome: I. Immunocytochemical evidence for a T‐cell–mediated immune effector response

Specimens of muscle and fascia from 13 patients fulfilling the Centers for Disease Control criteria for the eosinophilia myalgia syndrome (EMS) were studied by quantitative immunocytochemical analysis. The immunolocalization of CD3, CD4, CD8, CD22, and CD56 markers, the γδ T‐cell receptor, major histocompatibility complex (MHC) class I complex and class II antigens, and complement membrane attack complex (MAC) were examined. The distribution and relative proportions of T cells and T‐cell subsets, B cells, macrophages, and eosinophils were determined at perivascular, perimysial, endomysial, and fascial sites of accumulation. At all sites, T cells were predominant, CD8+ cells outnumbered CD4+ cells 6‐ to 20‐fold, and between 60 and 80% of T cells were activated. B cells and eosinophils each accounted for less than 3% of inflammatory cells. Very few cells expressed either the γδ T‐cell receptor or natural killer cell markers. As in dermatomyositis (DM), MHC class I antigen complex expression was increased on many structurally normal muscle fibers, but in contrast to DM, microvascular MAC deposits were not a feature of EMS. The findings implicate a cellular immune response directed against a connective tissue component in EMS.