Abstract
Inflammation underlying immune pathology and tissue damage involves an intricate interplay between multiple immunological and biochemical mediators. Cytokines represent the key immune mediators that trigger a cascade of reactions that drive processes such as angiogenesis and proteolytic damage to tissues. IL-17 has now been shown to be a pivotal cytokine in many autoimmune diseases, supplanting the traditional Th1-Th2 paradigm. Also, the dual role of proinflammatory IFN-γ has unraveled new complexities in the cytokine biology of such disorders. A major hurdle in fully understanding the effector pathways in these disorders is the lack of information regarding the temporal kinetics of the cytokines during the course of the disease, as well as the interplay among the key cytokines. Using an experimental model of arthritic inflammation, we demonstrate that the temporal expression of cytokines during the incubation phase is a critical determinant of disease susceptibility. The susceptible rats raised a vigorous IL-17 response early, followed by IFN-γ and IL-27 response in that sequence, whereas the resistant rats displayed an early and concurrent response to these three cytokines. Accordingly, treatment with exogenous IFN-γ/IL-27 successfully controlled arthritic inflammation and inhibited the defined mediators of inflammation, angiogenesis, cell survival, apoptosis, and tissue damage. Furthermore, IFN-γ enhanced IL-27 secretion, revealing a cooperative interplay between the two cytokines. Our results offer a novel immunobiochemical perspective on the pathogenesis of autoimmune arthritis and its therapeutic control.