Role of cytokine p40 family in multiple sclerosis

Over the last couple of decades of neuro-immunological research, the p40 family of cytokines has emerged out as one of the most intriguing areas of interest because of multi-faceted roles of these cytokine in immune-modulation and inflammation. The IL-12, the most widely studied cytokine of this family, is well-characterized for its Th1-favoring activity, and therefore plays a key role in the pathophysiology of Th1-mediated autoimmune diseases like multiple sclerosis (MS). On the other hand, the IL-23, another member of the p40 family with shared p40 subunit, drives polarization of Th17, a subset of T cell suspected to have a key role in the pathophysiology of MS and experimental allergic encephalomyelitis (EAE), poses a challenge to our current understanding of Th1/Th2 hypotheses in autoimmune diseases. However, the more puzzling issues, the researchers are currently confronted with, are the biological roles of other two members of this family, the p40 monomer and the p40₂, the homodimer. Predominance of the mRNA level of p40 over p35 in the central nervous system of EAE and MS suggests a possible involvement of p40 in the pathogenesis of MS. However, the distinctive biological role of monomelic and dimeric form of p40 is not clearly understood yet. Initially, it was thought that p402 does not have any biological activity and only in volved in antagonizing bioactive IL-12 but according to recent evidences, both p402 and p40 appear to have a proinflammatory role, therefore might be a crucial molecule in the pathogenesis of MS. The current review focuses on biological function of p40 family of cytokines with particular emphasis on MS.