The effect of interleukin 17 and Toll-like receptor 2 on CD11b expression and apoptosis of neutrophils in zymosaninduced arthritis and paw oedema.

We investigated the effect of interleukin (IL)-17 on Ly6G+ cell apoptosis in zymosan-induced arthritis (ZIA) and oedema (ZIO). Zymosan injection at the ankle joint caused swelling and coincided with histological joint alterations and IL-17A expression in areas with cell infiltrates. Flow cytometry of blood demonstrated increased frequencies of Ly6G+CD11b+ cells and their decreased apoptosis in ZIA. Annexin V+ neutrophils had lower CD11b expression, unlike Annexin V− cells. Cell survival for 12 hours was affected neither by IL-17 nor by zymosan alone, while both stimuli diminished Annexin V+ cell frequencies and up-regulated CD11b on Annexin V− cells. Interleukin 17 antagonised to the effects of zymosan in 24-hour cultures. The administration of IL-17 in ZIO increased paw thickness, enlarged the blood Ly6G+ pool, elevated CD11b expression and decreased apoptosis. We suggest that altered neutrophil apoptosis in arthritis can be overcome by anti-IL-17 therapy combined with an inhibition of Toll-like receptor (TLR) 2 and CD11b signalling.