Inflammatory neutrophils retain susceptibility to apoptosis mediated via the Fas death receptor

Abstract

Apoptosis and clearance of neutrophils is essential for successful resolution of inflammation. Altered signaling via the Fas receptor could explain the observed prolongation of neutrophil lifespan and associated tissue injury at inflammatory sites. We therefore compared inflammatory neutrophils extracted from joints of rheumatoid arthritis patients, with peripheral blood neutrophils. Inflammatory neutrophils underwent constitutive apoptosis in culture more rapidly than peripheral blood neutrophils; this was not explained by changes in surface expression of Fas or by induction of Fas ligand. Inflammatory neutrophils remained sensitive to Fas-induced death, at levels comparable to those seen in peripheral blood neutrophils. Similarly, granulocyte-macrophage colonystimulating factor reduced apoptosis but did not abolish signaling via Fas. These data provide evidence for the rate of apoptosis in inflammatory neutrophils being continually modulated by death and survival signals in the inflammatory milieu. This allows for rapid resolution of inflammation as levels of survival factors fall, and suggests new strategies for inducing resolution of inflammation.

Induction of Neutrophil Apoptosis by thePseudomonas aeruginosaExotoxin Pyocyanin: A Potential Mechanism of Persistent Infection

“…1-HP, a pyocyanin degradation product, was without effect upon neutrophil apoptosis. The proapoptotic effect of pyocyanin is far greater than, for example, that achieved by ligation of the death receptor, Fas (12), and neutrophils showed far greater sensitivity to pyocyanin than did macrophages or epithelial cells. Induction of neutrophil apoptosis by pyocyanin occurred in the presence of concentrations of LPS known to inhibit constitutive neutrophil apoptosis (4, 24) and did not differ in neutrophils from cystic fibrosis patients compared with healthy controls.…”

“…Neutrophils were suspended at a concentration of 2.5 ϫ 10 6 /ml in RPMI 1640, with 10% FCS and with penicillin and streptomycin (100 U/L; all from Life Technologies, Glasgow, U.K.) (12). The age of neutrophils in culture was calculated, designating this stage as time 0.…”

“…At the time points indicated, apoptosis was quantified by assessment of nuclear morphology on Giemsa-stained cytocentrifuge preparations, counting Ͼ300 cells per slide on duplicate cytospins with the observer blinded to cell treatment (1,12). This method has been shown to correlate closely with other measurements of neutrophil apoptosis, including annexin V binding (17) and shedding of CD16 (18).…”

“…significant quantities by P. aeruginosa (25,26). Antiapoptotic factors have been shown to inhibit apoptosis when added along with a proapoptotic stimulus, with Fas-mediated neutrophil apoptosis being inhibited by coadministration of a range of different antiapoptotic stimuli (12,27). We therefore sought to investigate whether P. aeruginosa LPS could inhibit the proapoptotic effect of pyocyanin in coculture experiments (Fig.…”

Constitutive neutrophil apoptosis: Mechanisms and regulation

“…Neutrophils constitutively express high levels of Fas and Fas ligand (FasL), and are highly susceptible to rapid apoptosis after stimulation with FasL or activating anti-Fas IgM. Spontaneous neutrophil death in vitro can be partially blocked by Fas/FasL pathway antagonists [92][93][94]. Fas engagement by agonistic anti-Fas antibody leads to enhanced caspase-8 and -3 activation and augmented mitochondrial permeability.…”