IL23A encodes the p19 subunit of interleukin-23 (IL-23), a pro-inflammatory cytokine that associates with IL12B to form a heterodimeric complex 1. IL-23 is produced primarily by antigen-presenting cells including dendritic cells and macrophages 2, and signals through a heterodimeric receptor (IL12RB1/IL23R) to activate JAK2 and TYK2 kinases, ultimately phosphorylating STAT3 and STAT4 345. This cascade activates downstream pathways including p38 MAPK and NF-κB, promoting pro-inflammatory cytokine production, particularly IL-17A 6. IL-23 drives expansion and survival of pathogenic T-helper 17 (Th17) cells and other IL-17-producing lymphocytes 7. In disease, CD14+ dendritic cells co-producing IL1B and IL23A are enriched in psoriatic lesions 2, while regulatory mechanisms involving CTLA-4+ ILC3s restrain IL-23-mediated pathology 8. Clinically, IL-23 inhibitors—particularly p19-targeted monoclonal antibodies like risankizumab—achieve superior efficacy in psoriasis and inflammatory bowel disease, with >70% of psoriasis patients achieving PASI 90 responses and durable clinical benefit 910. IL-23 also contributes to chemotherapy-induced cognitive dysfunction through endothelial STAT3-dependent signaling 11, indicating roles beyond immune-mediated inflammation.