Regulation of Interleukin 12 p40 Expression through an NF-κB Half-Site

Abstract

Interleukin 12 (IL-12) is an inducible cytokine composed of 35-and 40-kDa subunits that is critical for promoting T helper type 1 development and cell-mediated immunity against pathogens. The 40-kDa subunit, expressed by activated macrophages and B cells, is induced by several pathogens in vivo and in vitro and is augmented or inhibited by gamma interferon (IFN-␥) or IL-10, respectively. Control of IL-12 p40 expression is therefore important for understanding resistance and susceptibility to a variety of pathogens, including Leishmania major and perhaps human immunodeficiency virus. In this report, we provide the first characterization of IL-12 p40 gene regulation in macrophages. We localize inducible activity of the promoter to the sequence ؊122 GGGGAATTTTA؊132 not previously recognized to bind Rel family transcription factors. We demonstrate binding of this sequence to NF-B (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-B family members in IL-12 p40 activation. Finally, we find that IFN-␥ treatment of cells enhances this binding interaction, thus potentially providing a mechanism for IFN-␥ augmentation of IL-12 production by macrophages.Interleukin 12 (IL-12) production by macrophages is critical in induction of T helper type 1 (Th1) cells during initial immune responses to pathogens (5,15,21,32,45). Th1 cells produce gamma interferon (IFN-␥) and IL-2, which promote macrophage activation and cytolytic T-cell maturation, thus generating effective cell-mediated responses to intracellular pathogens (33, 37). The macrophage is the principal source of IL-12 production in responses to certain intracellular pathogens, such as Listeria monocytogenes (20,21,48). Recently, Chehimi and colleagues described diminished IL-12 production by macrophages in human immunodeficiency virus-infected individuals (2) and proposed that this may contribute to reduced cell-mediated immunity seen in AIDS (6, 7). Thus, understanding IL-12 production by macrophages, and its inhibition in settings of disease, could contribute to immune response-based therapies or vaccine designs.IL-12 is an inducible, heterodimeric, disulfide-linked cytokine composed of 35-and 40-kDa subunits encoded by separate genes (5,19,24,43,49). Expression of the 35-kDa subunit is constitutive and ubiquitous. In contrast, the 40-kDa subunit is expressed only by macrophages and B cells; it is strongly induced by several bacterial stimuli and is considered the regulatory component for IL-12 expression (11). Further, we and others have found that some cytokines, notably IFN-␥ and IL-10, can exert their effects on T-cell responses by augmenting or inhibiting macrophage production of 21,26). To date, the transcriptional regulation of p40 gene induction by bacteria and by cytokines is uncharacterized.In this report, we demonstrate several important features of IL-12 p40 gene regulation in macrophages. First, we localize the inducible promoter activity for the p40 gene to a nov...

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“…26,27) Expression of the p35 subunit is constitutive and ubiquitous. Therefore, the biological activity of IL-12 is mainly regulated by the induction of p40, 27) which is regulated primarily at the transcriptional level. Note that since IL-12 is a key cytokine in Th1-mediated autoimmune responses, downregulation of IL-12 production by the isolated compounds from the soft coral S. maxima may ameliorate autoimmune diseases.…”

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