TNF-INDUCED SUPEROXIDE ANION PRODUCTION IN ADHERENT HUMAN NEUTROPHILSINVOLVES BOTH THE P55 AND P75 TNF RECEPTOR

TNF, a potent activator of neutrophil granulocytes, acts via two cell- surface receptors: the p55-TNF receptor (TNF-R55) and the p75-TNF rece ptor (TNF-R75), which can be cleaved from the cell surface and thus fo rm soluble TNF-binding proteins (TNF-BP). The role of the two receptor s in activation of the neutrophil respiratory burst was investigated. Two mAbs reacting with TNF-R55 (H398 and TBP2) induced O-2 release in a similar manner but to a lesser extent than TNF. TBP2, however, requi red preincubation at 4 degrees C to exert its effect. Preincubation of neutrophils (both at 4 and 37 degrees C) with mAb to TNF-R75 decrease d TNF-induced superoxide anion production by 67 and 64%, respectively, indicating the essential role also for TNF-R75 in neutrophil activati on. This inhibitory effect could not be explained by cross-down-regula tion of TNF-R55 because the TNF-R75 mAb had no effect on TNF binding t o TNF-R55 as determined by binding of I-125-labeled TNF or release of TNF-R55-BP as measured by ELISA. Furthermore, the TNF-R75 mAb did not decrease superoxide anion generation induced by the TNF-R55 mAb H398, thus ruling out that the inhibitory effect of the TNF-R75 mAb is due t o inhibition of the signaling pathway downstream of TNF-R55. In contra st to the TNF-R75 mAb, TNF-R55 mAbs induced down-regulation of TNF-R75 and shedding of both TNF-R55-BP and TNF-R75-BP. We conclude that both TNF-R55 and TNF-R75 are involved in TNF-induced activation of the neu trophil respiratory burst.