Human CD1c (BDCA-1)+ myeloid dendritic cells secrete IL-10 and display an immuno-regulatory phenotype and function in response to Escherichia coli

Human blood myeloid DCs can be subdivided into CD1c (BDCA-1)+ and CD141 (BDCA-3)+ subsets that display unique gene expression profiles, suggesting specialized functions. CD1c+ DCs express TLR4 while CD141+ DCs do not, thus predicting that these two subsets have differential capacities to respond to Escherichia coli. We isolated highly purified CD1c+ and CD141+ DCs and compared them to in vitro generated monocyte-derived DCs (MoDCs) following stimulation with whole E. coli. As expected, MoDCs produced high levels of the proinflammatory cytokines TNF, IL-6, and IL-12, were potent inducers of Th1 responses, and processed E. coli-derived Ag. In contrast, CD1c+ DCs produced only low levels of TNF, IL-6, and IL-12 and instead produced high levels of the anti-inflammatory cytokine IL-10 and regulatory molecules IDO and soluble CD25. Moreover, E. coli-activated CD1c+ DCs suppressed T-cell proliferation in an IL-10-dependent manner. Contrary to their mouse CD8+ DC counterparts, human CD141+ DCs did not phagocytose or process E. coli-derived Ag and failed to secrete cytokines in response to E. coli. These data demonstrate substantial differences in the nature of the response of human blood DC subsets to E. coli.