FUNCTIONAL-ANALYSIS OF COMPLEMENT RECEPTOR-1 USING A NEW MONOCLONAL-ANTIBODY, KUN241

A monoclonal antibody (MAb), KuN241, recognized an antigen present on all monocytes, polymorphonuclear leukocytes (PMNs), B cells, and a sub population of T cells, Cell surface expression pattern and immunopreci pitation studies indicated the molecule recognized by KuN241 to be com plement receptor 1 (CR1), This was confirmed by sequential immunopreci pitation using Ell, a CR1-specific monoclonal, and by immunoprecipitat ion analysis of a truncated transfection product of CR1, In vitro acti vation of PBLs for 7 days with pokeweed mitogen (PWM) abrogated surfac e expression of CR1 on B cells, Overnight culture with phorbol 12-myri state 13-acetate (PMA) downregulated the expression of CRI detected by KuN241 both on PMNs and monocytes, Addition of MAb KuN241 to purified PMN and monocytes resulted in a transient increase in intracellular c alcium ([Ca2+](i)). This was blocked by the Fab fragment of MAb KuFc79 directed against the Fc gamma receptor, Further, Fab fragment of KuN2 41 cross-linked with F(ab')(2) goat anti-mouse Ig failed to increase [ Ca2+](i) levels, Taken together, these results suggested a novel mecha nism for transmembrane signaling events by dual binding of KuN241, the Fab region to CR1 and the Fc region to Fc gamma RII.