Inhibitory role of interleukin-10 in the cutaneous reverse Arthus reaction

The formation and deposition of immune complexes (IC) containing immunoglobulin (Ig)G antibodies induces an acute inflammatory response with tissue injury. One of the experimental models of IC-related vasculitis is the cutaneous reverse passive Arthus reaction, in which IgG antibodies are injected i.d., followed immediately by the i.v. application of the corresponding antigen. This reaction is characterized by edema, hemorrhage and neutrophil infiltration. To assess the role of the anti-inflammatory cytokine interleukin (IL)-10 in IC-related vasculitis, we investigated the cutaneous Arthus reaction using IL-10 knockout (IL-10KO) mice. Edema, which was quantified macroscopically by measuring the vascular leakage of Evans blue dye at 4 h after IC challenge, was significantly increased in IL-10KO mice compared with wild-type mice. In addition, hemorrhage, which was assessed by the average diameter of purpuric spots at 8 h after IC challenge, was enhanced significantly in IL-10KO mice compared with wild-type mice. Histological examination showed that the number of extravascular neutrophils was significantly increased in IL-10KO mice compared with wild-type mice at 4 and 8 h after IC challenge. Analysis of pro-inflammatory cytokine mRNA expression showed that IL-6 mRNA levels were significantly increased in IL-10KO mice compared with wild-type mice at 4 and 8 h after IC challenge. These results showed that IC-induced inflammation and vascular damage were significantly enhanced in the absence of IL-10. Thus, IL-10 may limit tissue disruption by suppressing the excessive infiltration of neutrophils and cytokine expression in a mouse model of type III vasculitis.