On the origin of surface proteinase 3 of nonmyeloid cells: evidence favoring an exogenous source

In Wegener's granulomatosis (WG), when the endogenous Proteinase 3 (PR3) of myeloid cells is translocated to the cell surface, a pathologically consequent interaction is believed to occur with classic anti-neutrophil cytoplasmic antibody (cANCA). In contrast, the exact origin of surface PR3 on cells of nonmyeloid origin is still debated. By various methods, PR3 mRNA and protein are easily demonstrated in myeloid cells but not in nonmyeloid cells. Exceptionally, the endothelial ECV304 cell line spontaneously produced PR3 mRNA but no PR3 protein. In the other nonmyeloid cells, we could not show cell surface PR3 either spontaneously or after TNFalpha stimulation. On the other hand, under serum-free conditions and using [(3)H]DFP-labeled HL-60 extract, a rapid, dose-dependent, saturable binding was demonstrated to both myeloid and nonmyeloid cells. That was reproduced with purified [(3)H]DFP-PR3. While we could not demonstrate cell surface PR3 on nonmyeloid cells after incubation with serum-containing supernatants of HL-60 cell cultures, we could do so after an overnight coculture period with HL-60 cell suspensions under the usual serum-containing culture conditions. Overall, our data would suggest that in vivo, the surface PR3 found on nonmyeloid cells is not endogenous but results from adsorption of PR3 extruded in their microenvironment by neighboring myeloid cells coming in close contact with them.