Comprehensive Sequence Analysis of the Human IL23A Gene Defines New Variation Content and High Rate of Evolutionary Conservation

A newly described heterodimeric cytokine, interleukin-23 (IL-23) is emerging as a key player in both the innate and the adaptive T helper (Th)17 driven immune response as well as an initiator of several autoimmune diseases. The rate-limiting element of IL-23 production is believed to be driven by expression of the unique p19 subunit encoded by IL23A. We set out to perform comprehensive DNA sequencing of this previously under-studied gene in 96 individuals from two evolutionary distinct human population groups, Southern African Bantu and European. We observed a total of 33 different DNA variants within these two groups, 22 (67%) of which are currently not reported in any available database. We further demonstrate both inter-population and intra-species sequence conservation within the coding and known regulatory regions of IL23A, supporting a critical physiological role for IL-23. We conclude that IL23A may have undergone positive selection pressure directed towards conservation, suggesting that functional genetic variants within IL23A will have a significant impact on the host immune response.