IL17A and rheumatoid arthritis: Many miRNAs are involved in immune system development and also regulate the immune system; for example, miR-150 is critical for B cell differentiation [61], miR-155 promotes autoimmune inflammation [62], and miR-146a regulates the T-cell mediated T helper-1 (Th-1) response [63] and is expressed in interleukin-17 (IL-17)-producing Th-17 cells in rheumatoid arthritis [64].