Mouse strain differences in plasmacytoid dendritic cell frequency and function revealed by a novel monoclonal antibody

We report in this study the generation of a novel rat mAb that recognizes mouse plasmacytoid dendritic cells (pDC). This Ab, named 120G8, stains a small subset of CD11clow spleen cell with high specificity. This population produces high amounts of IFN- upon in vitro viral stimulation. Both ex vivo- and in vitro-derived 120G8 cells display a phenotype identical with that of the previously described mouse pDC (B220highLy6ChighGr1lowCD11bCD11clow). Mice treated with 120G8 mAb are depleted of B220highLy6ChighCD11clow cells and have a much-reduced ability to produce IFN- in response to in vivo CpG stimulation. The mAb 120G8 stains all and only B220highLy6ChighCD11clow pDC in all lymphoid organs. Immunohistochemical studies performed with this mAb indicate that pDC are located in the T cell area of spleen, lymph nodes, and Peyer’s patches. Although the Ag recognized by 120G8 is not yet known, we show that its expression is up-regulated by type I IFN on B cells and DC. Using this mAb in immunofluorescence studies demonstrates strain- and organ-specific differences in the frequency of pDC and other DC subsets. 129Sv mice have a much higher frequency of pDC, together with a lower frequency of conventional CD8CD11chigh DC, compared with C57BL/6 mice, both in spleen and blood. The higher ability of 129Sv mice to produce IFN- in vivo is related to a higher number of pDC, but also to a higher ability of pDC from 129Sv mice to produce IFN- in vitro in response to viral stimulation. The Journal of Immunology, 2003, 171: 6466–6477. D endritic cells (DC)2 are APCs that initiate T cell-depen-dent immune responses (1). In humans, plasmacytoidDC (pDC) are a DC subset characterized by their ultra-structural resemblance to Ig-secreting plasma cells, their uniqu