IL23 p40&p19, also known as interleukin-12 subunit beta/interleukin-23 subunit alpha, is a heterodimeric cytokine composed of two disulfide-linked subunit, a p19 subunit that is unique to IL23, and a p40 subunit that is shared with IL12. The p19 subunit has homology to the p35 subunit of IL12, as well as to other single chain sytokines sub as IL6 and IL11. It is produced by macrophages and B lymphocytes and has multiple effects on T-cells and NK cells, including stimulation of cytotoxic activity, proliferation, and promotion of Th1 development as well as IFN-gamma and TNF production. Recombinant human IL23 p40&p19, fused to His-tag at C-terminus, was expressed in insect cell and purified by using conventional chromatography techniques.