Considering the role of inflammatory processes in depression, the study aimed to verify the association of altered inflammatory processes (altered peripheral gene expression of inflammatory mediators) with major depressive disorders (MDD) by measuring changes in the levels of inflammatory indicators (IL-17, IL-21, IL-23, IL-35 and Foxp3), important in various types of autoimmune diseases, like rheumatoid arthritis (RA) and multiple sclerosis (MS). The gene discussed is IL21; the disease is autoimmune disease.