TRANSIENT INHIBITION OF CAPACITATIVE CALCIUM-ENTRY IN HUMAN NEUTROPHILS BY A MONOCLONAL-ANTIBODY DIRECTED AGAINST A 19-KDA ANTIGEN

P1C3 is a monoclonal antibody that binds p19, a novel neutrophil activ ation antigen that translocates to the cell surface upon neutrophil ac tivation. We find that P1C3 inhibits capacitative Ca2+ entry, induced by emptying the intracellular Ca2+ stores with thapsigargin. The effec t is transient, reaching its maximum at 30-60 s, but becomes permanent upon pretreatment of the cells with the protein phosphatase inhibitor calyculin A, suggesting the involvement of protein phosphorylation. T he inhibitory action is similar to the one reported previously for the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP), a lthough the transduction mechanism may be different. Inhibition of Ca2 + entry by fMLP was prevented by pretreatment with pertussis toxin, wh ereas inhibition by P1C3 was not. Pretreatment with cholera toxin had no effect. This suggests that the effect of P1C3 may not be mediated b y a heterotrimeric G protein. Tyrosine kinase inhibitors did not preve nt inhibition by either fMLP or P1C3. Phospholipase C activation seems not to be involved as P1C3, contrarily to fMLP, was unable to induce Ca2+ release from the intracellular Ca2+ stores.