The p28 subunit of interleukin-27 (IL-27), also known as interleukin-30 (IL-30), is a member of the interleukin-12 (IL-12) family of cytokines. p28 is a 28 kDa polypeptide that associates with the Epstein-Barr virus induced gene 3 (EBI-3) to form the IL-27 cytokine heterodimer complex. IL-27 functions as a proinflammatory cytokine that induces immunomodulatory effects in naive CD4+ T cells, mast cells, and monocytes. p28 can also form a complex with Cytokine-Like Factor 1 (CLF), that is secreted by dendritic cells, to regulate Natural Killer (NK) and T cell function.