Regulatory effects of interleukin-4 and interleukin-10 on human neutrophil function ex vivo and on neutrophil influx in a rat model of arthritis

Objective To assess the capacity of interleukin-4 (IL-4) and IL-10 to block polymorphonuclear neutrophil (PMN) activation in an ex vivo human model system, and to confirm their effect on neutrophil function in an animal model of arthritis. Methods The ex vivo phagocytic capacity of cytokine-activated human PMNs was assessed by use of assays for measuring the ingestion of heat-killed yeast and by subsequent hexose-monophosphate shunt activation using nitroblue tetrazolium reduction. The in vivo activity of IL-4 and IL-10 was measured using a rat adjuvant arthritis model in which the mycobacterial antigen concentration was titrated to modify disease intensity. Results IL-4 and IL-10 suppressed the ex vivo activation state of interferon-γ– and tumor necrosis factor α–activated human neutrophils. In the rat adjuvant arthritis model, treatment with systemic murine IL-10 (mIL-10) effectively suppressed all disease parameters in rats that received the lower concentrations of mycobacteria, whereas systemic mIL-4 was effective against even the most severe disease. Both cytokines were effective in lowering the absolute PMN cell number recovered and the PMN activation state in the joint synovia. We also observed lower levels of the messenger RNA transcript for CINC protein (cytokine-induced neutrophil chemoattractant; a rat homolog for human IL-8) in the synovia. Conclusion IL-10 is an effective antiarthritic agent and has a major effect on the presence and function of PMNs in the joint synovia when disease intensity is not severe. IL-4 has an inhibitory profile that is similar to that of IL-10, but is effective in modifying even the most severe disease. Both cytokines reduced the phagocytic activation of human PMNs in response to proinflammatory cytokines. These data demonstrate that IL-4 and IL-10 can exert powerful regulatory effects on neutrophil function that translate into a therapeutic response in a disease model of arthritis. Treatment with these cytokines alone or in combination may therefore be very useful in the management of patients with rheumatoid arthritis.