IN-VIVO REGULATION OF RAT NEUTROPHIL APOPTOSIS OCCURRING SPONTANEOUSLY OR INDUCED TH TNF-ALPHA OR CYCLOHEXIMIDE

We previously demonstrated that human TNF-alpha induces rapid apoptosi s of human neutrophils. To understand better the in vivo significance of neutrophil apoptosis, we examined spontaneous, recombinant human an d mouse TNF-alpha- or cycloheximide-induced apoptosis of normal periph eral blood neutrophils (PBN), PBN from rats injected i.p. with proteos e peptone or a streptococcus preparation, OK-432 (inflammatory PBN), p eritoneally exudated neutrophils (PBN) obtained after a proteose pepto ne injection, and normal bone marrow neutrophils. The following observ ations were made. 1) Normal PBN responded to TNF-alpha, but PBN, norma l bone marrow neutrophils, and inflammatory PBN at 12 h after stimulat ion did not. 2) The sensitivity to TNF-alpha of the inflammatory PBN s tarted to decrease at 3 h, was lowest at 12 h, and was almost restored at 52 h after stimulation. 3) Spontaneous apoptosis of normal and inf lammatory PBN reached 25% at 12 h after in vitro incubation, but that of PBN and normal bone marrow neutrophils was very low over this perio d. 4) The sensitivity to cycloheximide (6 h incubation) was high for n ormal PBN and bone marrow neutrophils, but low for PBN and inflammator y PBN after 12 h. 5) I-125-hTNF-alpha binding of bone marrow neutrophi ls was significantly lower than that of normal and inflammatory PBN an d PBN. 6) TNF-alpha-induced apoptosis of normal or inflammatory PBN an d bone marrow neutrophils was enhanced by treatment with low doses of cycloheximide that alone were barely able to induce neutrophil apoptos is; however, apoptosis of PBN was not. The mechanisms and in vivo sign ificance of these phenomena are discussed.