Interleukin-40 (IL-40)

Interleukin-40 (IL-40), encoded by the C17orf99 gene on chromosome 17q25.3, is a recently identified small secreted cytokine unique to mammals, primarily expressed in bone marrow, fetal liver, and activated B cells, with a pivotal role in the regulation of humoral immunity. IL-40 modulates B cell differentiation and maturation, stimulates IgA synthesis, and participates in maintaining B cell homeostasis, with important links to the composition of the gut microbiome and mammary gland function. It becomes upregulated in several inflammatory and autoimmune conditions, such as rheumatoid arthritis, where it correlates with disease activity and tissue remodeling. IL-40 is also implicated in B cell lymphoma biology and may play roles in mucosal immunity and antiviral responses. Structurally, it lacks homologs in other cytokine families ("orphan cytokine"), and its mechanisms of action and therapeutic potential remain under active investigation

Other names

C17orf99IL-40IL40chromosome 17 open reading frame 99UNQ464GLPG464Interleukin 40Protein IL-40uncharacterized protein C17orf99

Not directly targeted by known drugs; biological effects modulated via antibody-based therapies affecting B cells (e.g., rituximab); would act via cytokine-receptor interaction if a drug is developed