Interleukin-12 protein molecule. Molecular model of a molecule of the cytokine protein interleukin-12 (IL-12). The secondary structure of the molecule is seen here, containing alpha helices (spirals) and beta sheets (arrows). IL-12 is a cytokine (signalling compound) that is produced by dendritic cells and macrophages in the body when they encounter pathogens such as bacteria and viruses. IL-12 is involved in the development and function of T-cells. T-cells are white blood cells that are responsible for destroying pathogens. IL-12 also activates other cytokines, which go on to initiate other immune response molecules. This domino effect is known as a cascade.