Acute toxoplasma myositis: an immunohistochemical and ultrastructural study.

The occurrence is reported of acute myositis in a man with meningoencephalitis due to toxoplasmosis. The ultrastructure and immunohistochemistry of a muscle biopsy of the patient were investigated. Toxoplasma organisms were not found in the muscle biopsy. The perivascular inflammatory cells in the muscle were mainly CD4+ T cells and the inflammatory cells in and around the muscle fibres were chiefly macrophages. Expression of major histocompatibility complex class I and II antigens was observed in the infiltrating cells and endothelial cells of the blood vessels. A small proportion of the infiltrating cells expressed interferon-gamma. A possible role of the immune mechanism in the evolution of myositis is discussed.