Distribution of a formalin-resistant myelomonocytic antigen (L1) in human tissues. I. Comparison with other leukocyte markers by paired immunofluorescence and immunoenzyme staining.

L1 is an approximately 36-kd protein recently identified as a cytoplasmic and surface marker antigen of virtually all resting peripheral blood neutrophils and monocytes. This study of its tissue distribution showed that L1 is particularly well preserved in formalin-fixed and paraffin-embedded routine material. It had a restricted distribution within the monocyte-derived cell lineage, being mainly confined to reactive histiocytes (infiltrating macrophages). L1 was a much more reliable marker for such cells than lysozyme, except that the latter was better expressed by epithelioid and giant cells. L1 was lacking in HLA-DR-positive interdigitating, Langerhans', and most intestinal histiocytic cells. The same was true for Kupffer cells in normal livers; but in livers of three patients with malignant histiocytosis or histiocytic medullary reticulosis infiltrating histiocytes and putative Kupffer cells stained positively. Follicular dendritic cells and tangible body macrophages were always questionably L1 positive.