Immunohistochemical determination of immunosuppressive acidic protein in reactive and neoplastic diseases of macrophage.

Immunosuppressive acidic protein (IAP), a substance purified from cancer ascitic fluid, is released into the culture medium of macrophages and neutrophils, and is supposed to suppress an immune function of the host. Elevation of serum IAP in cancer patients has been reported. In the current study, presence of IAP in proliferating diseases of macrophage was examined. Macrophages in reactive proliferation, histiocytosis X, and neoplastic proliferation gave positive reaction for IAP. Diffuse cytoplasmic staining was usual, but dot-like or globular and surface staining also were observed. Proliferating cells in malignant fibrous histiocytoma were more sensitively stained by IAP than by other ordinary used markers for macrophage. These findings provide useful information to understand the mechanism of elevation of serum IAP in cancer patients.