The mechanism of macrophage activation induced by Ca2+ ionophore

The mechanism of macrophage activation by Ca2+ ionophore was studied. Peritoneal exudate macrophages from normal guinea pigs exposed continuously to or pulse treated for 1 hr with the ionophore, A23187, were activated, manifesting increased glucose consumption and inhibition of migration. Highly purified macrophages were also activated as effectively as crude macrophage preparations, and the culture supernatant of spleen lymphocytes treated with A23187 lacked a macrophage activating effect, showing that the macrophage activation resulted from the direct effect of A23187 on macrophages, not via lymphokines produced by lymphocytes. The macrophage activation by A23187 was suppressed in the presence of EGTA, but the suppressive effect was overcome by the addition of Ca2+, but not of Mg2+. A dilution experiment with Ca2+ and Mg2+ during the pulse treatment of cells with A23187 revealed that the activating effect of A23187 was more dependent on Ca2+ content than Mg2+. In addition, the Ca2+ antagonist, nicardipine, was found to suppress the activating effect of A23187. The Ca2+ uptake into macrophages was increased by treatment with A23187. These results indicate that Ca2+ influx into cells is primarily important in the macrophage activating effect of A23187. Trifluoperazine (TFP: a specific inhibitor of calmodulin that is an intracellular Ca2+ receptor protein) was found to inhibit the activating effect of A23187. Further, the cyclic nucleotides, dibutyryl-cAMP and -cGMP, did not activate macrophages. Therefore, macrophage activation was presumed not to be directly mediated by cyclic nucleotides. All these findings show that macrophage activation with the ionophore proceeds by the following scheme: Ca2+ influx leads to activation of Ca2+ receptor protein, calmodulin leads to activation of calmodulin-regulated enzymes leads to metabolic changes, activation. TFP was found to suppress the macrophage activation with highly purified guinea pig macrophage activation factor/macrophage migration inhibitory factor (MIF/MAF) or lipopolysaccharide (LPS), suggesting that calmodulin also played an important role in macrophage activation with MIF/MAF or LPS.