The high-affinity FcγRI on PMN:: regulation of expression and signal transduction

In this paper we report that interferon-gamma(IFN-gamma) maintains and enhances functional properties of terminally differentiated polymorphonuclear cells (PMN). Such effects are obvious when compared with untreated PMN declining in their functional response. Culture for 18 hr with 100 IU/ml of recombinant IFN-gamma resulted in the expression of about 15 000 Fc gamma RI per PMN. IFN-gamma maintained viability of PMN and prevented reduction of Fc gamma RIIIb caused by apoptosis. No alterations were found in the level of Fc gamma RIIa. Next, functional properties of Fc gamma RI were evaluated. Calcium mobilization was detected in fura-2/acetoxymethylester (AM)-loaded PMN using a spectrophotometer and the respiratory burst was measured as luminol-dependent chemiluminescence. Crosslinking of an F(ab')(2) fragment of monoclonal antibody (mAb) 22.2 to Fc gamma RI gave similar results to those obtained with intact monomeric human immunoglobulin G (mhIgG) when subsequently cross-linked. Moreover, after blocking Fc gamma RIIa and Fc gamma RIIIb with respective mAb fragments, mhIgG was still effective in triggering a calcium flux demonstrating that second messenger generation was caused by Fc gamma RI engagement. Even though Fc gamma RI expression was lower than that of Fc gamma RIIa, Fc gamma RI induced a higher increase of the respiratory burst. In addition, the protein tyrosine phosphatase CD45 was able to inhibit both responses when it was cc-cross-linked with CD64, suggesting involvement of tyrosine phosphorylation in early signalling steps.