Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine. MIF is involved in the innate immune response to bacterial pathogens. The e, Xenopus/Amphibian,pression of MIF at sites of inflammation suggests a role as mediator in regulating the function of macrophages in host defense. Genetic variations in MIF are associated with susceptibility to rheumatoid arthritis systemic juvenile (RASJ). RASJ is an inflammatory articular disorder with systemic-onset beginning before the age of 16.