REGULATION OF INTERLEUKIN-12 P40 EXPRESSION THROUGH AN NF-KAPPA-B HALF-SITE

Interleukin 12 (IL-12) is an inducible cytokine composed of 35- and 40 -kDa subunits that is critical for promoting T helper type 1 developme nt and cell-mediated immunity against pathogens. The 40-kDa subunit, e xpressed by activated macrophages and B cells, is induced by several p athogens in vivo and in vitro and is augmented or inhibited by gamma i nterferon (IFN-gamma) or IL-10, respectively, Control of IL-12 p40 exp ression is therefore important for understanding resistance and suscep tibility to a variety of pathogens, including Leishmania major and per haps human immunodeficiency virus. In this report, we provide the firs t characterization of IL-12 p40 gene regulation in macrophages. We loc alize inducible activity of the promoter to the sequence (-122)GGGGAAT ITTA(-132) not previously recognized to bind Rel family transcription factors, We demonstrate binding of this sequence to NF-KB (p50/p65 and p50/c-Rel) complexes in macrophages activated by several p40-inducing pathogens and provide functional data to support a role for NF-kappa B family members in IL-12 p40 activation. Finally, we find that IFN-ga mma treatment of cells enhances this binding interaction, thus potenti ally providing a mechanism for IFN-gamma augmentation of IL-12 product ion by macrophages.