IL-17A

Class

Interleukin inhibitor

Interleukin-17A (IL-17A) is a signaling protein, or cytokine, produced mainly by a subset of immune cells called T helper 17 (Th17) cells, as well as by certain innate immune cells. It acts on receptors present on skin cells, epithelial cells, and fibroblasts, triggering release of additional inflammatory mediators and recruitment of neutrophils, a type of white blood cell involved in acute inflammation. This cytokine is a central driver of chronic inflammatory diseases in which the skin, joints, or gut barrier are affected, including psoriasis, psoriatic arthritis, and ankylosing spondylitis. In these conditions, IL-17A is produced in excess and sustains a self-reinforcing cycle of tissue inflammation, thickened skin, and joint damage. Blocking IL-17A directly, most commonly with monoclonal antibodies that bind the cytokine and prevent it from engaging its receptor, interrupts this cycle and reduces downstream inflammatory signaling. Because IL-17A also has a normal physiological role in defending against certain fungal and bacterial infections at skin and mucosal surfaces, its inhibition is a targeted way to dampen pathological inflammation while leaving most other immune functions intact, though it carries a recognized trade-off in host defense at those specific barriers.