Rheumatoid arthritis exacerbation caused by exogenous interleukin-12.

Interleukin-12 (IL-12) is a pleiotropic cytokine with proinflammatory, immunoregulatory, antitumor, and antimetastatic properties. It plays a crucial role in the development of the Th1 response and subsequent interferon-gamma production and enhancement of cell-mediated cytotoxicity. Recently, IL-12 has been used as an experimental therapy for cancer. Given the multiple immunomodulatory properties of IL-12, there are potential concerns associated with its clinical use. Of special interest are the possible side effects of IL-12 therapy in patients with autoimmune diseases, especially those that are T cell mediated, such as rheumatoid arthritis (RA). We present a case of severe RA exacerbation caused by treatment with IL-12 for metastatic cervical cancer. This is the first reported case of RA flare caused by exogenous IL-12.