p40

Bioactive interleukin-12 p70 (IL-12p70) is a heterodimer composed of 2 subunits: p35 and p40. Although p35 is expressed in numerous cell types, p40 expression is more restricted and determines the ability of a given cell-type to produce bioactive IL-12. However, in the cells that are capable of producing both IL-12 subunits, it is the p35 subunit, produced in much lower amounts than p40, that plays the role of a limiting factor and determines the amount of bioactive IL-12p70 that is secreted. IL-12p70 heterodimer is a major Th1-driving cytokine. In contrast, p40 homodimer, secreted by antigen presenting cells (APCs) in the absence of p35 production, and to a lesser extent the p40 monomer, were shown to act as antagonists of mouse and human IL-12 receptors and to inhibit IL-12–dependent immune functions in vitro and in vivo.

p40;