Interaction of proteinase 3 with CD11b/CD18 (2 integrin) on the cell membrane of human neutrophils

Abstract: Proteinase 3 (PR3), the target autoan-tigen of antineutrophil cytoplasmic antibodies in the autoimmune vasculitis, Wegener’s granuloma-tosis, is a serine proteinase stored in granules of human neutrophils. As previously shown, PR3 is expressed also on the plasma membrane of unac-tivated neutrophils, and this expression increases in primed or stimulated cells. The current study demonstrates that membrane-bound PR3 colocal-izes with the adhesion molecule CD11b/CD18 (2 integrin). Immunoprecipitation experiments using plasma membranes of phorbol 12-myristate 13-acetate (PMA)-stimulated neutrophils revealed co-immunoprecipitation of PR3 with CD11b/CD18, indicating their location in the same complex. PR3 was also detected in TritonX-100-insoluble cy-toskeleton of plasma membranes isolated from un-activated and activated neutrophils. Release of cy-toskeletal PR3 by salt treatment implied electro-static interaction with the enzyme. The serine protease inhibitor phenylmethylsulfonyl fluoride (PMSF) augmented membrane expression of PR3 in unactivated and PMA-stimulated neutrophils. PMSF significantly reduced adhesion of neutro-phils to fibrinogen-coated plates and their NADPH oxidase activity. Moreover, the addition of exoge-nous PR3 (1–5 g/ml) augmented the CD11b/ CD18-dependent adhesion of neutrophils. Taken together, these results implicate the 2 integrin of neutrophils in their membrane association with PR3 and suggest a role of PR3 in the modulation o