Interleukin-12 (IL-12) is a potent regulator of cell-mediated immune responses. Biologically active IL-12 is secreted by activated B lymphocytes and macrophages as a 70 kD heterodimeric glycoprotein comprised of disulfide-bonded 35 kD (p35) and 40 kD (p40) subunits. IL-12 binds to specific high affinity receptors and can; i) stimulate the growth of activated CD4+ and CD8+ T cells and natural killer (NK) cells; ii) promote the development of proinflammatory/Th1-like CD4+ cells and cytotoxic CD8+ T cells; iii) increase the lytic activity of NK cells, lymphokine-activated killer cells and antibody dependent cell-mediated cytotoxic cells, and; iv) induce NK and T cells to secrete large amounts of the proinflammatory cytokine, IFN-γ. Recombinant mouse IL-12 p70 (Cat. No. 554592) is provided lyophilized, containing bovine serum albumin and no preservatives. Recombinant mouse IL-12 p70 was found to be ≥ 95% pure as determined by SDS-PAGE, and an absorbance assay based on the Beer-Lambert law. The endotoxin level is ≤ 0.1 ng per μg of mouse IL-12 p70, as measured in a chromogenic LAL assay.