Characterization of regulatory dendritic cells differentiated from the bone marrow of UV-irradiated mice.

When antigen-loaded dendritic cells (DCs) differentiated from the bone marrow (BM) of UV-irradiated mice (UV-BMDCs) were adoptively transferred into naive mice or mice pre-sensitized with that antigen, the recipients exhibited a reduced immune response following antigen challenge. Hence, UV-BMDCs are poorly immunogenic and can suppress pre-existing immunity. The UV-induced effect on BM-derived DCs was rapid (observed 1 day after UV radiation), long-lasting (observed 10 days after UV radiation) and UV dose-dependent. The mechanism by which UV-BMDCs could regulate immunity was investigated. The CD11c(+) cells, differentiated using granulocyte-macrophage colony-stimulating factor + interleukin-4, were confirmed to be DCs because they did not express the myeloid-derived suppressor cell marker, Gr1. UV-BMDCs did not display altered antigen uptake, processing or ability to activate T cells in vitro. When gene expression in UV-BMDCs and DCs differentiated from the BM of non-irradiated mice (control-BMDCs) was examined, Ccl7, Ccl8 and CSF1R (CD115) mRNA transcripts were up-regulated in UV-BMDCs compared with control-BMDCs. However, neutralizing antibodies for Ccl7 and Ccl8 did not abrogate the reduced immunogenicity of UV-BMDCs in vivo. Moreover, the up-regulation of CSF1R transcript did not correspond with increased receptor expression on UV-BMDCs. The phenotypes of UV-BMDCs and control-BMDCs were similar, with no difference in the expression of CD4, CD8α, CD103, B220 or F4/80, or the regulatory molecules CCR7 (CD197), FasL (CD95L), B7H3 (CD276) and B7H4. However, PDL1 (CD274) expression was reduced in UV-BMDCs compared with control-BMDCs following lipopolysaccharide stimulation. In summary, UV-BMDCs do not express the classical phenotypic or gene expression properties of DCs reported by others as 'regulatory' or 'tolerogenic'.