Detection of proteolytic (C 3‐cleaving) activity on mouse mastocytoma (P815) cells and other mouse cell lines by formation of cell contact with C 3‐carrying mouse lymphocytes

Abstract

Mouse mastocytoma cells (P815) formed rosettes with normal mouse spleen lymphocytes which had been coated with uncleaved human C 3; this interaction was clearly dependent on the amount of C 3. Lymphocytes treated with C 3 b or buffer alone were ineffective. Formation of cell contact could be inhibited by the presence of protease inhibitors such as diisopropyl fluorophosphate, phenyl methyl sulfonyl fluoride and tosyllysyl chloromethyl ketone. Seven out of 13 different cell lines behaved like P 815 cells. The results strongly suggested that a proteolytic activity on mouse tumor cells led to a cooperation with uncleaved C3 on a carrier cell to connect these two cells. We interpreted these data in analogy to the complement‐dependent bridge formation mechanism (M. P. Dierich and B. Landen, J. Exp. Med. 1977. 146: 1484): uncleaved C3, attached to mouse spleen lymphocytes as carriers, becomes cleaved by enzymes associated with the tumor cells tested; by this cleavage, the labile binding site is released on C3 (nascent C3b) and anchors the C3‐carrying cell to the protease‐ carrying cell; since this labile binding site is short‐lived, this process can be induced by membrane‐associated proteases only. The nature of the proteases and the biological implications of this process are as yet uncertain.