funding sources include cancer institute new south wales ( cinsw ) career development and support fellowship to v.m.h . , cinsw scholar award and australian rotary health phd scholarship to e.a.t .
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 .