IL23A (Interleukin-23 subunut alpha) is a cytokine that functions in the inflammatory and immune responses to infection and also promotes angiogenesis. Loss of IL23A leads to inflammatory bowel disease and experimental autoimmune encephalomyelitis in mice. It is also implicated in the pathogenesis of immune and inflammatory diseases such as spondyloarthritis and psoriatic arthritis. Inherited mutation and separately upregulation in IL23A are implicated in multiple sclerosis and immune inflammatory disease. In immunohistochemistry, IL23A has cytoplasmic positivity in immune cells and most tissues throughout the body. References: Current Opinion in Immunology. 18 (6): 670–5. doi:10.1016/j.coi.2006.09.008, PMID: 17010592; Nature. 442 (7101): 461–5, PMID: 16688182; Arthritis Rheumatol. 2014 Feb;66(2):231-41, PMID: 24504793; International Journal of Rheumatology. 2012 (539683), DOI: 10.1155/2012/539683; Aging (Albany NY). 2016 Nov; 8(11): 2734–2744; Brain. 2007. 130 (2): 490–501, DOI: 10.1093/brain/awl273;