Figure 4.

PC-lineage cells are enriched in the LZ after depletion of CD4⁺ Tfh cells and colocalize with FDCs. (A and B) GC responses were established from SW_HEL.Blimp1^gfp/+ B cells and subjected to 3-d treatment with either anti-CD40L (A) or anti-CD4 (B) as outlined in Fig. 3. (Left) Representative flow cytometry profiles indicate the impact of mAb treatments on the LZ and DZ phenotypes of IgG1⁺ PC-lineage cells (Blimp1-GFP⁺). (Right) The proportions of IgG1⁺ PC-lineage cells that fell within the DZhi, DZlo, LZhi, and LZlo compartments in individual recipients were also enumerated. (C) Immunofluorescence histology of spleens from recipient mice 9 d after transfer of SW_HEL B cells plus HEL^3X-SRBCs and 3 d after injection of isotype control or anti-CD4 mAb. The B cell follicle (Fo) is marked by IgD (white), the LZ by CD35 (FDCs; red), and the DZ by CXCR4 (blue). The unstained T cell zone (TZ) is also indicated. IgG1⁺ PC-lineage cells are identifiable by bright (cytoplasmic) staining (green). Frequencies of IgG1⁺ PC-lineage cells identified within the LZ (containing CD35⁺ FDCs) by immunofluorescence analysis were 7% (5/66) in isotype-treated and 69% (76/110) in anti-CD4–treated mice (enumerated over 17 and 16 individual GCs, respectively). Bars, 50 µm. Data are representative of two to four independent experiments of five mice per group (A and B) or are representative of four independent experiments of five mice per group (C). P-values were calculated using an unpaired Student’s t test. ***, P < 0.001.