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Selective Suppression of IL-12 Production by Chemoattractants

Immune Cell Interaction Unit, Mucosal Immunity Section, Laboratory for Clinical Investigation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892

We investigated the ability of chemoattractants to affect IL-12 production by human monocytes and dendritic cells. We found that pretreatment of monocytes with macrophage chemoattractant proteins (MCP-1 to -4), or C5a, but not stromal-derived factor-1, macrophage inflammatory protein-1, RANTES, or eotaxin, inhibited IL-12 p70 production in response to stimulation with Staphylococcus aureus, Cowan strain 1 (SAC), and IFN-. The production of TNF- and IL-10, however, was minimally affected by any of the chemoattractants. The degree of inhibition of IL-12 p70 production by MCP-1 to -4 was donor dependent and was affected by the autocrine inhibitory effects of IL-10. In contrast, C5a profoundly suppressed IL-12 production in an IL-10-independent fashion. Neither TGF-ß1 nor PGE₂ was important for the suppression of IL-12 by any of the chemoattractants tested. The accumulation of mRNA for both IL-12 p35 and p40 genes was inhibited by chemokine pretreatment. Interestingly, MCP-1 to -4 and C5a did not suppress IL-12 production by monocyte-derived dendritic cells (DC) stimulated with CD40 ligand and IFN- or by SAC and IFN-, suggesting that these factors may act at the site of inflammation to suppress IL-12 and IFN- production rather than in the lymph node to affect T cell priming. Despite the inability of C5a to inhibit IL-12 production by DCs, the receptor for C5a (CD88) was expressed by these cells, and recombinant C5a induced a Ca²⁺ flux. Taken together, these results define a range of chemoattractant molecules with the ability to suppress IL-12 production by human monocytes and have broad implications for the regulation of immune responses in vivo.