Naturally occurring CD1c+ human regulatory dendritic cells: immunoregulators that are expanded in response to E. coli infection.

Dendritic cells (DCs) play key roles in initiating and regulating immunity by sensing and integrating signals from a wide range of pathogens and dangers. Although much knowledge has been gained about the origins, phenotypes, and functions of mouse DC subsets, the challenge now is to translate this knowledge to the human immune system and reveal relevant biological significance in human health and disease. Considerably less is known about the phenotype and function of human DC subsets due to their rarity, the lack of distinctive markers, and limited access to human tissues. Initial studies of DCs in human blood revealed that steady-state myeloid DCs are comprised of the CD141(+) and CD1c(+) DC subsets as the equivalents to the mouse lymphoid resident CD8(+) and CD8(-) DC subsets, respectively. A new report in this issue of the European Journal of Immunology [Eur. J. Immunol. 2012. 42: 1512-1522] shows that human CD1c(+) myeloid DCs secrete IL-10 and display an immunoregulatory phenotype and function in response to Escherichia coli (E. coli). This finding adds a new element to the current understanding of human CD1c(+) DCs and reveals marked differences in human DC subsets during inflammation and microbial infection, as discussed in this Commentary.