KP1: a new monoclonal antibody that detects a monocyte/macrophage associated antigen in routinely processed tissue sections.

A new monoclonal antibody, KP1, raised against a lysosomal fraction of human lung macrophages, recognises a fixation-resistant epitope in a wide variety of tissue macrophages (such as Kupffer cells germinal centre, splenic, and lamina propria macrophages), and in granulocyte precursors. Its broad reactivity with cells of the mononuclear phagocytic lineage was established by testing on routinely processed samples of normal and reactive lymphoid tissues. Interdigitating reticulum cells were unstained or showed limited cytoplasmic staining while Langerhans' cells and follicular dendritic reticulum cells were unreactive. KP1 recognises a molecule of about 110 kilodaltons in macrophage-rich human tissue when tested by either immunoprecipitation or Western blotting (although the latter procedure also shows two additional components with molecular weights of 70 and 40 kilodaltons). KP1 should be of considerable value for studying disorders of the monocyte/macrophage system, including both reactive and neoplastic states (such as true histiocytic proliferations).