Suppression of collagen-induced arthritis by continuous administration of IL-4

The onset of collagen-induced arthritis in DBA/1 mice is accompanied by a predominantly Th1 response, characterized by production of the proinflammatory cytokines IFN-gamma and TNF-alpha, and a predominance of IgG2a anti-collagen Abs. This study has primarily addressed the effects of continuous administration of exogenous IL-4, a Th2 cytokine, on collagen-induced arthritis in terms of time of onset, clinical symptoms, and histologic changes compared with those in untreated controls. The contributions of Th1 and Th2 cell responses were studied by examining anti-CII IgG subclasses, serum IgE levels, and cytokine production by synovial membrane and lymph node cell cultures. Continuous exposure to IL-4 for 28 days significantly delayed the onset of arthritis from 19 to 37 days and suppressed clinical symptoms. Arthritis occurred approximately 13 to 24 days after treatment ceased. Thereafter, the severity and duration of clinical symptoms were similar to those in control animals, although both joint damage and inflammation at the histologic and cellular levels were less severe than those in untreated controls. During IL-4 treatment, anti-collagen Ab levels were reduced (most significantly those of the IgG2a subclass), histology scores were lower, and the most striking effect was a 1000-fold decrease in TNF-alpha secretion by synovial cells. No significant differences in IgE levels were found between controls and IL-4-treated mice. These data suggest that the anti-inflammatory properties of IL-4 are mediated in part by down-regulation of Th1 responses rather than up-regulation of Th2 responses.