Interleukin 12 (IL-12) is a 70 kDa cytokine produced principally by macrophages, neutrophils and dendritic cells in response to stimulation by antigen. IL-12 is a T cell-stimulating factor, playing a critical role in the regulation of T-helper 1 cell responses. IL-12 is composed of two subunits, p35 and p40, covalently linked by a single disulfide bond. The p40 subunit, which binds to the receptor chain IL-12Rβ1, is shared with another heterodimeric cytokine, IL-23. However, the two cytokines expert distinct non-redundant biological functions (1). Therapeutic agents targeting both IL-12 and IL-23 cytokines are currently used to treat psoriasis and psoriatic arthritis, and related agents are in clinical testing for a variety of inflammatory disorders (2). iLite? IL-12 Assay Ready Cells are a genetically engineered reporter gene cell line (DT-40, ATCC#CRL-2111) responsive to Interleukin-12 by specific and proportional expression of Firefly Luciferase. Normalization of cell counts and serum matrix effects is obtained by a second reporter gene, a Renilla Luciferase reporter gene construct, under the control of a constitutive promotor.