Brief Deﬁnitive Report CD47 Ligation Selectively Downregulates Human Interleukin 12 Production By Myriam Armant, Marie-Noëlle Avice, Patrice Hermann, Manuel Rubio, Mamoru Kiniwa, Guy Delespesse, and Marika Sarfati From Laboratoire Allergie, Centre de Recherche du Centre Hospitalier de l’Université de Montréal (CHUM), Campus Notre-Dame, Quebec H2L 4M1, Canada Summary Interleukin (IL)-12 plays a key role not only in protective innate and adaptive T helper cell type 1 (Th1) responses but also in chronic inflammatory diseases. We report here that engagement of CD47 by either monoclonal antibody, its natural ligand thrombospondin (TSP), or 4N1K (a peptide of the COOH-terminal domain of TSP selectively binding CD47) inhibits IL-12 release by monocytes. The suppression occurred after T cell–dependent or –independent stimulation of monocytes and was selective for IL-12 inasmuch as the production of tumor necrosis factor (TNF)-a, IL-1, IL-6, and granulocyte/macrophage colony-stimulating factor was not inhibited. CD47 ligation did not alter transforming growth factor (TGF)-b and IL-10 production, and the suppressive effect on IL-12 was not due to autocrine secretion of TGF-b or IL-10. The IL-12 inhibition was not mediated by Fcg receptor ligation, did not require extracellular Ca21 influx, but was reversed by two phosphoinositide 3-kinase inhibitors (wortmannin and Ly294002). Thus, engagement of CD47 on monocytes by TSP, which transiently accumulates at the inflam- matory site, is a novel and unexplored pathway to selectively downregulate IL-12 response. The pathway may be relevant in limiting the duration and intensity of the inflammatory response, and in developing novel therapeutic strategies for Th1-mediated diseases. Key words: CD47 • interleukin 12 • monocytes • thrombospondin Imunoregulatory cytokine which plays a crucial role in nterleukin (IL)-12 is a potent proinflammatory and im- innate and adaptive immunity (for a review, see reference 1). IL-12 is produced primarily by activated mononuclear and polynuclear phagocytes, as well as dendritic cells. IL-12 is released during the early stage of infections caused by a large variety of bacteria, intracellular pathogens, fungi, and certain viruses. This early production of IL-12 is T cell in- dependent and results from the direct interaction of patho- gens or their products with phagocytic cells. IL-12 rapidly triggers NK cells and T cells to release IFN-g, which in- creases not only the bactericidal activity of phagocytes but also their release of proinflammatory cytokines, including IL-12 itself. In addition to activating the cells of the innate immune system, IL-12 and IFN-g direct the differentiation of antigen-specific naive T cells into Th1 effectors, produc- ing high levels of IFN-g and conferring protection against intracellular pathogens. The IL-12/IFN-g proinflammatory loop initiated during the early stage of infection is generally of short duration and is probably downregulated by several mechanisms. For example, the engagement of phagocytic receptors (CR3, Fcg, and scavenger receptors) on macrophages by opsonized bacteria was shown to inhibit IL-12 production (2, 3). Sim- ilarly, CD46 ligation by measle virus suppresses IL-12 release (4). Another important physiological inhibitor of IL-12/ IFN-g production is IL-10, which can also be released by pathogen-stimulated phagocytes, but at a later stage than IL-12 (1). Other nonselective inhibitors of IL-12 produc- tion include cytokines like TGF-b, IL-4, and IL-13, as well as PGE2, glucocorticoids, and cholera toxin (5–7). IL-12 is also produced after cognate interaction of CD41 T cells with dendritic cells or monocytes (8). This T cell– dependent pathway of IL-12 production is mediated through CD40–CD154 (CD40L) interactions and regulates the level of IFN-g production in primary and secondary response to antigens devoid of intrinsic adjuvant activity, including au- toantigens (1). Recent evidence further suggests a third mechanism of IL-12 production which may occur at in- flammatory sites, without infectious agents or TCR-medi- ated signals (9). It was found that the addition of IL-15 or IL-2 to cultures of autologous resting T cells and mono- cytes induces the production of proinflammatory cytokines including IL-12 and IFN-g. The extravasation of T lymphocytes and monocytes from blood vessels to inflammatory lesions requires interac- tions with the extracellular matrix (ECM), which is com- posed of various adhesive glycoproteins and glycosamino- 1175 J. Exp. Med. The Rockefeller University Press • 0022-1007/99/10/1175/07 $5.00 Volume 190, Number 8, October 18, 1999 1175–1181 http://www.jem.org