PMN-derived proteases enhance the affinity of Fcγ receptor II on myeloid cells, but not on B cells

Treatment of monocytes or K562 cells with proteolytic enzymes like pronase or trypsin, increases both the affinity of the type II Fc receptor for IgG and the signaling via this receptor. In the present study we evaluated whether other proteases could similarly enhance Fcγ RII affinity. We furthermore assessed whether all cell types expressing Fcγ RII display this effect. Therefore, proteins from the coagulation system and PMN-derived enzymes were tested for effects on Fcγ RII-mediated ligand binding. Enzymes of the coagulation system were tested both in fibrinogen-depleted plasma, as well as in purified form. No effects were found on Fcγ RII-mediated rosette formation for both situations. In contrast, supernatant of stimulated granulocytes as well as leucocyte elastase were observed to be active in augmenting EA-hIgG rosette formation of thrombocytes and myeloid cell lines K562 and U937. The B cell lines Raji and Daudi, did not show enhanced rosette formation after enzyme treatment. The active component from granulocyte supernatant was partially characterized as a serine esterase with an apparent Mw of 30 kD. We tested whether the isotype specificity of Fcγ RII on K562 cells changes upon enzyme treatment. It was found that all three tested murine subclasses γ 1, γ 2a, γ 2b, bound equally well to this receptor, and interaction with all isotypes was enhanced to the same extent.