ACTIVATION AND PRIMING OF HUMAN MONOCYTES BY MONOCYTE CHEMOTACTIC ANDACTIVATING FACTOR - COOPERATION WITH OTHER INFLAMMATORY CYTOKINES ANDCLOSE ASSOCIATION BETWEEN AN INCREASE IN CYTOPLASMIC FREE CA2+ AND INTRACELLULAR ACIDIFICATION

Both monocyte chemotactic and activating factor (MCAF) and N-formyl-me thionyl-leucyl-phenylalanine (FMLP) stimulated an increase in cytoplas mic free Ca2+ ([Ca2+](i)) and changes in intracellular pH (pHi) in hum an monocytes in parallel at lower concentrations and stimulated supero xide (O-2(-)) release and changes in transmembrane potential in parall el at higher concentrations. The changes in pHi were characterized by initial rapid acidification followed by sustained alkalinization, and the changes in transmembrane potential were characterized by initial d epolarization followed by partial repolarization. The time courses of all responses stimulated by MCAF and FMLP were similar to each other, although the magnitude of all responses was less in MCAF-stimulated ce lls. MCAF by itself was a very weak stimulus for inducing O-2(-) relea se. However, MCAF primed monocytes and enhanced O-2(-) release stimula ted by FMLP. The priming effect of MCAF was maximal within 5 minutes o f preincubation, and the dose-response curves for priming were identic al to those for triggering of an increase in [Ca2+](i). Treatment of m onocytes with the intracellular Ca2+ chelator, ,2-bis(2-aminophenoxy)e thane-N,N,N',N'-tetraacetic acid (BAPTA), abolished not only the incre ase in [Ca2+](i) but also the changes in pHi (both acidification and a lkalinization) induced by MCAF or FMLP. MCAF further potentiated FMLP- induced O-2(-) release in tumor necrosis factor (TNF)-, granulocyte-ma crophage colony-stimulating factor (GM-CSF)-, or IL-3-primed monocytes . These findings suggest that MCAF, alone or in concert with other cyt okines, primes monocytes for enhanced release of O-2(-), and that MCAF - or FMLP-induced intracellular acidification and alkalinization are c losely associated with an increase in [Ca2+](i), but not O-2(-) releas e.