A small subpopulation of CD11c1 cells acquires proteins from fluorescent-labeled B cells. Purified HEL-specific transgenic B cells on the C57Bl/6 (H-2bb) background were labeled with CFSE, loaded with HEL, and adoptively transferred into unmanipulated B10.BR (H-2kk) recipients. 12 h later the mice were killed and the spleens were gently prepared, stained, and analyzed by flow cytometry. The very bright CFSE+, CD11c− population represents the transferred B cells (0.08%). Data were gated using a wide FSC, SSC gate which included lymphocytes, large cells, and granular cells. Dead cells were eliminated from the analysis by negative gating using 7-AAD. Data are representative of 20 independent experiments. (B) CFSE-labeled B cells are not adhered to the surface of the DCs. The CFSEhi transferred B cells and the CD11c+, CFSEmed populations identified in Fig. 2 were analyzed for the expression of the B cell marker, B220, by flow cytometry. Data were gated as in Fig. 2. The data are representative of three independent experiments.