When first reported, EBM/l1 reacted with mononuclear phagocyte system cells only in fresh frozen sections, but it has been shown to have similar cellular specificity in routine formalin fixed, paraffin wax embedded tissue. This was achieved by limited proteolysis with protease XIV before immunocytochemical staining. In archival biopsy specimens EBM/ll produced granular cytoplasmic staining of alveolar macrophages, Kupffer cells, tingible body macrophages and sinus histiocytes, cells of splenic cords, cortical and medullary macrophages of thymus; blood monocytes, peritoneal and mesothelial macrophages; bone marrow mononuclear cells, megakaryocytes and osteoclasts; lamina propria macrophages in the gastrointestinal tract, and connective tissue cells (presumptive macrophages) of thyroid, gall bladder, skin, pancreas, ovary, myometrium, endometrium, cervix, kidney, prostate, placenta, myocardium and breast. Unlike other anti-macrophage antibodies, EBM/ll did not react with granulocytes, lymphocytes, plasma cells, platelets, endothelial and epithelial cells in paraffin wax sections. It did not label skin Langerhans' cells, microglial cells, and interdigitating reticulum cells (as in frozen sections). This study opens a new area for the specific identification by EBM/11 of mononuclear phagocyte system cells in archival biopsy specimens. It also raises the possibility that some monoclonal antibodies, believed to be reactive only in frozen sections, may react in archival tissue after limited proteolysis with an appropriate enzyme.
