Soluble Fc gamma receptor IIIb alters the function of polymorphonuclear neutrophils but extends their survival

We have established that polymorphonuclear neutophil (PMN)-binding anti-Fc gamma receptor IIIb (Fc gamma RIIIb) autoantibodies (autoAb) inhibit the fu nction of these cells but extend their survival. Here, we show that recombi nant FcyRIIlb (rFc gamma RIIIb), as well as purified Fc gamma RIIIb (pFc ga mma RIIIb), deteriorated the PMN adherence and respiratory burst in a dose- dependent manner. Furthermore, rFc gamma RIIIb and pFc gamma RIIIb reduced the level of annexin V-binding PMN from 23.6 +/- 1.6 % to 6.3 +/- 1.0 and 1 1.0 +/- 1.0 %, respectively, while human serum albumin exerted no effects, incubation of rFc gamma RIIIb with those autoAb binding to soluble Fc gamma RIIIb resulted in the attachment of such immune complexes (IC) to the cell s, thereby also delaying apoptosis (44.9 +/- 5.9 versus 18.0 +/- 2.0 % anne xin V-binding PMN after 16 hours). Soluble Fc gamma RIIIb, in concert with Fc gamma RIIIb/anti-Fc gamma RIIIb IC, produced similar effects in that the percentage of annexin V-bindingi PMN declined to 16.0 +/- 1.9 %. it was th us suggested that Fc gamma RIIIb/antiFc gamma RIIIb IC inserted the Fc regi on of their IgG into the membrane Fc gamma RIIIb. Such an interpretation is consistent with our finding that, whereas aggregated IgG and anti-Fc gamma RIIIb monoclonal Ab prevented membrane Fc gamma RIIIb/IC interaction, neit her soluble Fc gamma RIIIb, nor antiFc gamma RII did so. We conclude that t he function and the life span of PMN are influenced synergistically by solu ble Fc gamma RIIIb and anti-Fc gamma RIIIb autoAb.