FC-GAMMA-RII-MEDIATED SUPEROXIDE PRODUCTION BY PHAGOCYTES IS AUGMENTED BY GM-CSF WITHOUT A CHANGE IN FC-GAMMA-RII EXPRESSION

Freshly purified neutrophils and monocytes respond to multiple cross-linking of FCγRII with the IgG1 monoclonal antibody, CIKM5, with a rapid rise in Ca(2+)(i), but not with a respiratory burst, although superoxide is generated by these cells when stimulated with the chemotactic peptide, FLMP, or phorbol ester (TPA). Incubation in vitro for 30-60 min at 37°C in medium + 0.1% FCS had no effect on the neutrophil superoxide response to CIKM5 but induced a weak monocyte response in 11/13 experiments. However, incubation with rhGM-CSF (10 ng/ml) under similar conditions induced a neutrophil respiratory burst in response to cross-linking FcγRII in 12/14 experiments and enhanced the monocyte response by 181%. GM-CSF also enhanced the response of neutrophils and monocytes to FMLP by 308% and 165%, respectively. The response to TPA was not signicantly enhanced by GM-CSF. rhIFN-γ (100 u/ml) was ineffective as a priming agent for all agonists tested in short-term incubations but augmented the monocyte response to CIKM5 after 5 d exposure in vitro. Whilst GM-CSF induced neutrophil superoxide production in response to cross-linking FcγRII, there was no concomitant change in FcγRII expression either in in vitro studies of neutrophils from healthy individuals or in in vivo studies of patients receiving GM-SCF. Stimulation of unprimed neutrophils with CIKM5 induced a rapid transient increase in intracellular calcium levels to 181% of resting levels. However, incubation with GM-CSF did not further augment the calcium transients above the stimulated level. The mechanism by which GM-CSF induces an enhanced respiratory burst in response to cross-linking of FcγRII remains to be elucidated, but is not related to receptor expression or increases in receptor mediated calcium mobilization.