[Effect of Interleukin-17 on neutrophil apoptosis].

OBJECTIVE: To study the effect of Interleukin(IL)-17 on neutrophil apoptosis and try to explain the possible mechanism involved. METHODS: Neutrophils isolated from healthy donors were incubated in enriched RPMI 1640 cell culture medium at 37 degrees C in 5% carbon dioxide. Subgroups were incubated with IL-17, heat-denatured IL-17 (X-IL-17), dexamethasone (DEX), or buffer alone. Apoptosis was assessed by morphologic changes, by detecting DNA strand breaks. Production of proapoptotic protein Bax by neutrophils was evaluated by immunocytochemistry. RESULTS: At the time of neutrophil incubation, neutrophils in the control subsets exhibited morphologic evidence of apoptosis. A steady rise in apoptosis index (AI) was noted, with (1.54+/-0.08)% for 0 h, (11.48+/-1.80)% (compared with 0 h, P<0.05) for 12 h and (34.19+/-1.92)% (compared with 0 h, P<0.01) for 24 h, respectively. IL-17 at concentration of 50 microg/L resulted in increased AI of neutrophils, with (1.43+/-0.17)% (compared with control 0 h, P>0.05) for 0 h, (20.47+/-6.22)% (compared with control 12 h, P<0.01) for 12 h and (40.74+/-3.48)% (compared with control 24 h, P<0.05) for 24 h, respectively. While at concentrations of 5 mug/L and 0.5 microg/L, IL-17 resulted in decreased AI, with (14.24+/-4.26)% (compared with control 24 h, P<0.01) for 24 h, and (19.86+/-4.39)% (compared with control 24 h, P<0.01) for 24 h, respectively. AI of neutrophils treated with X-IL-17 at concentration of 50 ng/ml for 24 h was (33.22+/-1.61)% (compared with control 24 h, P>0.05). Neutrophils apoptosis was accompanied by DNA fragmentation. In all groups, the increasing of Bax immunoreactivity was strongly related with more apoptotic neutrophils (r=0.932, P<0.01). CONCLUSION: In vitro, IL-17 modulates apoptosis of neutrophils. At higher concentrations, it accelerates neutrophils apoptosis. At lower concentrations, it delays neutrophils apoptosis. Modulation of the expression of Bax by IL-17 may be one of the possible inner mechanisms.