AZOTEMIA, TNF-ALPHA, AND LPS PRIME THE HUMAN NEUTROPHIL OXIDATIVE BURST BY DISTINCT MECHANISMS

The oxidative burst of neutrophils from azotemic patients (AzoPMNs) is primed for an enhanced response compared to neutrophils from normal s ubjects (NorPMNs). The mechanism for this priming is unknown, although TNF alpha does not further prime AzoPMNs. The present study examines the hypothesis that azotemia and TNF alpha prime neutrophils by the sa me mechanism. Formyl peptide receptor expression and degranulation wer e not primed in AzoPMNs, but were primed by both LPS and TNF alpha. LP S was also able to prime the AzoPMN oxidative burst. Guanine nucleotid e exchange by multiple guanine nucleotide binding proteins, including heterotrimeric G-proteins and low molecular weight GTP-binding protein s (LMWGs), was increased in AzoPMNs, as demonstrated by GTP gamma S bi nding and azidoanilide GTP photoaffinity labeling. The plasma membrane density of G-protein alpha(i2), alpha(i3), and alpha(s) subunits and the density in the cytosol of the LMWG, Rac2, did not differ between A zoPMNs and NorPMNs. However, the LMWG, Rap1A, was present in significa ntly greater amounts on plasma membranes from AzoPMNs. FMet-Leu-Phe-st imulated phospholipase D activity, but not basal activity, was signifi cantly greater in AzoPMNs. Finally, incubation of NorPMNs in plasma fr om azotemic patients resulted in a significant increase in basal GTP g amma S binding. These results demonstrate that priming of AzoPMNs is r estricted to oxidative burst activity and that it occurs by a mechanis m distinct from that utilized by TNF alpha and LPS. While the exact me chanism remains unknown, it appears to involve a plasma factor and cha nges in LMWG expression or activity.