IL-12 is an important type 1 immune activation cytokine. It is known that macrophages and dendritic cells the major cell types producing this cytokine and that these cells may release both the biologically inactive form (IL-12p40) and active form (IL-12p70) of IL-12. In this review, the latest information regarding the regulatory mechanisms governing the production of IL-12p70 by these cells is evaluated. (C) 2008 Elsevier Inc. All rights reserved.