Human IL-19 (Interleukin-19) is a member of the IL-10 cytokine family that functions primarily as an immunomodulatory cytokine involved in regulation of inflammatory responses. IL-19 is produced predominantly by monocytes, macrophages, epithelial cells, keratinocytes, and other tissue-resident cells in response to pro-inflammatory stimuli such as IL-1β and TNF-α. It signals through the heterodimeric IL-20 receptor complex (IL-20R1/IL-20R2), activating downstream pathways including STAT3, which contribute to modulation of cytokine production and immune cell activity. IL-19 is generally associated with Th2-skewed immune responses and can promote production of IL-4, IL-5, and IL-13 while dampening excessive Th1-mediated inflammation. In healthy individuals, circulating IL-19 levels are typically low but increase during inflammatory and autoimmune conditions. Elevated IL-19 expression has been implicated in psoriasis, atopic dermatitis, asthma, inflammatory bowel disease, rheumatoid arthritis, and certain cardiovascular and fibrotic disorders. In clinical and translational research, human IL-19 serves as a biomarker of immune dysregulation and epithelial inflammation and is being investigated as both a mediator and potential therapeutic target in chronic inflammatory and immune-mediated diseases.