Recombinant human tumor necrosis factor-α. Regulation of N-formylmethionylleucylphenylalanine receptor affinity and function on human neutrophils

Abstract

Preincubation of neutrophils with recombinant human tumor necrosis factor-α (rH TNF-α) enhanced the subsequent release of superoxide anion in response to various concentrations of N-formylmethionylleucylphenylalanine (FMLP). Enhanced superoxide anion production was evident by 5 min and had reached a plateau by 15 min. Not only was the total amount of superoxide anion released greater, but the rate of release was also enhanced threefold by rH TNF-α. In contrast, rH TNF-α reduced or abolished neutrophil locomotion under agarose in response to a gradient of FMLP. Binding studies of f-Met-Leu-[3H]Phe to purified human neutrophils revealed a heterogeneous binding to unstimulated cells. The high affinity component consisted of ~ 2,000 sites per cell and had an average K(d) of 2 ± 0.7 nM (n = 4). The low affinity component consisted of ~ 40,000 sites per cell and had an average K(d) of 180 ± 50 nM (n = 4). rH TNF-α caused conversion to a linear Scatchard plot showing no significant change in total binding sites but a single K(d) of 40 ± 10 nM (n = 4). These data indicate that rH TNF-α may influence neutrophil responses to FMLP by regulating the affinity of FMLP receptors.