One such pathway involves IL-17, a pro-inflammatory cytokine produced mainly by Th17 cells, which plays a complex role in both health and disease states.84 Chronic IL-17 activity is involved in the pathogenesis of inflammatory diseases, such as psoriasis, rheumatoid arthritis, and inflammatory bowel disease, while it also contributes to mucosal immunity by promoting antimicrobial peptide production and maintaining epithelial barrier integrity in the intestine.84,85 Similarly, the role of IL-17 in mood and behavior is paradoxical. The gene discussed is IL17A; the disease is rheumatoid arthritis.