Involvement of Syk in pathology of systemic autoimmune disease

Biological products have proven its high efficacy on autoimmune disease such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Meanwhile, small molecular drugs have attracted attention over the years because of its availability of oral administration and cost effectiveness. Spleen tyrosine kinase (Syk) is a 72 kDa protein tyrosine kinase widely expressed on cells that are involved in the immune system and inflammation such as B cells, T cells, macrophages and synovial fibroblast. Syk is involved in intracellular signaling of the multi-chain immune receptors, including B cell receptor (BCR), ξchain of T-cell receptor (TCR), FcR and integrins, which contains the immune-receptor tyrosine-based activation motif (ITAM). Recently, Syk inhibitor fostamatinib has exerted potent therapeutic efficacy against autoimmune and allergic diseases such as rheumatoid arthritis (RA), bronchial asthma and thrombocytopenic purpura (ITP). Moreover, Syk blockade prevented the development of skin and kidney lesions in lupus-prone mice, however the mechanism of action is unclear. We have revealed that Syk-mediated BCR-signaling is prerequisite for optimal induction of toll-like receptor (TLR)L9, thereby allowing e-cient propagation of CD40- and TLR9- signaling in human B cells. These results indicate that inhibition of Syk have a potential to regulate B-cell mediated inflammatory diseases such as SLE. We here document the in vitro and in vivo effects of a Syk inhibitor for the treatment of autoimmune diseases, mainly in RA and SLE.