SPONTANEOUS AND FAS-INDUCED APOPTOTIC CELL-DEATH IN AGED NEUTROPHILS

On the basis of the strict analogies between polymorphonuclear cell (P MN) alterations in the aging and depressed functional capacities displ ayed by apoptotic PMN, we investigated the possible occurrence of age- associated changes in neutrophil apoptosis, either spontaneous or indu ced by Fas antigen (CD95) activation. In both cases, old subjects exhi bited a time course kinetics of neutrophil apoptosis, as assessed by m orphologic and quantitative DNA fragmentation analysis, which overlapp ed that observed in the young. These findings were confirmed by DNA la dder analysis, showing a progressive increase in DNA cleavage products in cells cultured in medium alone or added with agonistic anti-Fas Ig M (CH-11) monoclonal antibodies (mAbs), after 12 and 6 hr of incubatio n, respectively. Aged purified neutrophils constitutively expressed CD 95, at levels similar to those observed in the young. Moreover, althou gh we failed to detect Fas ligand expression on PMN surface, treatment of cell cultures with antagonistic anti-Fas IgG1 (ZB4) mAbs determine d a significant inhibition of spontaneous apoptosis in neutrophils fro m both groups of subjects, thus suggesting that the Fas/Fas ligand sys tem is in fact involved in such an event. The results indicate that th e overall intrinsic mechanisms regulating neutrophil cell death are no t affected by age. Yet aged neutrophils showed a diminished capacity t o be rescued by proinflammatory mediators, such as granulocyte-monocyt e colony-stimulating factor, granulocyte colony-stimulating factor, an d bacterial lipopolysaccharide, following Fas activation. This may ham per the accumulation of functionally active cells in inflammatory area s in vivo, thus contributing to the increased susceptibility of elderl y individuals to life-threatening infections.