Identification of Interleukin 40, a novel B cell-associated cytokine.

Abstract

We have identified a novel mouse and human cytokine. IL-40 is normally produced in the bone marrow and fetal liver, and by activated B cells. Its sequence predicts a small (~27kDa) secreted protein unrelated to other cytokine gene families, that we have called Interleukin 40 (IL-40). IL40 is only present in mammalian genomes, suggesting a role in mammalian immune responses. Accordingly, IL-40 expression is induced in the mammary gland upon the onset of lactation, and an IL-40−/− mouse exhibits reduced levels of IgA in the serum, gut, feces, and milk. Furthermore, the IL-40−/− mouse has smaller and fewer Peyer’s patches and IgA secreting cells. The gut microbiome of IL-40−/− mice also exhibits altered composition, reflecting the reduced levels of IgA in the gut. We have also determined that B cell precursor populations are altered in the IL-40−/− mouse. Taken together, these observations indicate that IL-40 represents a novel B cell associated cytokine, that plays an important role in the development of humoral immune responses. IL-40 is also expressed by human activated B cells and by several human B cell lymphomas. The latter observation suggests that it may play a role in the pathogenesis of these diseases.