Interleukin-17 Acts Independently of TNF-α under Arthritic Conditions

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Abstract
The proinflammatory T cell cytokine IL-17 is a potent inducer of other cytokines such as IL-1 and TNF-α. The contribution of TNF in IL-17-induced joint inflammation is unclear. In this work we demonstrate using TNF-α-deficient mice that TNF-α is required in IL-17-induced joint pathology under naive conditions in vivo. However, overexpression of IL-17 aggravated K/B×N serum transfer arthritis to a similar degree in TNF-α-deficient mice and their wild-type counterparts, indicating that the TNF dependency of IL-17-induced pathology is lost under arthritic conditions. Also, during the course of the streptococcal cell wall-induced arthritis model, IL-17 was able to enhance inflammation and cartilage damage in the absence of TNF. Additional blocking of IL-1 during IL-17-enhanced streptococcal cell wall-induced arthritis did not reduce joint pathology in TNF-deficient mice, indicating that IL-1 is not responsible for this loss of TNF dependency. These data provide further understanding of the cytokine interplay during inflammation and demonstrate that, despite a strong TNF dependency under naive conditions, IL-17 acts independently of TNF under arthritic conditions.

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