Interleukin-17A (IL-17A), a central pro-inflammatory cytokine produced primarily by a subset of T helper cells called Th17 cells. IL-17A plays a pivotal role in the pathogenesis of psoriasis. It acts on keratinocytes (skin cells), fibroblasts, and other immune cells by binding to the IL-17 receptor complex. This binding triggers the production of numerous other inflammatory mediators (such as defensins, chemokines like CXCL1, and other cytokines like IL-6 and TNF-α), leading to neutrophil recruitment, keratinocyte proliferation, and sustained inflammation.