CD35⁺B220⁺ cells show FDC-M1⁺ phenotype in splenic white pulp. Transferred CD35⁺B220⁺cells showed the FDC-M1⁺ phenotype. Isolated CD35⁺B220⁺ cells labeled with PKH26 (A) or CD35⁺B220⁺ cells from GFP-Tg mice (B) were administered intravenously into naive C57BL/6J-Jcl mice. On day 15 after the adoptive transfer, cryosections of the spleen were examined by immunofluorescence staining with anti-FDC-M1 Ab and Alexa-Fluor-488–conjugated anti-GFP mAb. Anti-rat IgG conjugated with FITC (panel A) or anti-rat IgG conjugated with Cy3 (panel B) was used to visualize the microarchitecture of the splenic FDC-M1⁺ reticulum. Samples are representative of 3 independent experiments. All images were analyzed with a fluorescence microscope and were photographed with an Olympus fluorescence microscope. Bars, 200 μm. Shown in panels C and D are high-power photographs of the area enclosed by the yellow squares in panels A and B. Samples stained with antirat IgG conjugated with FITC (panel E, left) or anti-GFP IgG conjugated with Alexa Fluor 488 and antirat IgG conjugated with Cy3 (panel E, right) were used as control. Careful examination revealed that CD35⁺ cells showed the FDC-M1⁺ phenotype in splenic white pulp on day 15 after adoptive transfer.