Figure 1.

In the GC, CD23 is expressed in the LZ, mainly by FDCs but also by some B cells. (A) Immunofluorescence staining of CD23 (red), PAX5 (pink) and PD1 (green) in paraffin-embedded tonsil tissues; the white arrow shows a CD23⁺ B cell located in front of a PD1⁺ Tfh cell. (B) Immunofluorescence staining of CD23 (pink), PAX5 (red) and CD3 (green) on frozen tonsil tissues; the PAX5 staining pattern for B cells does not really match the CD23 marker; panels 1 & 2 show T cells surrounded by CD23⁺ dendritic extensions, and panels 3 & 4 show T cells in the vicinity of CD23^- B cells. (C) The proportion of CD23-expressing B cells was determined by flow cytometry in different B cell populations in tonsils (Right panel) and rLNs (Left panel): CD19⁺CD38^-IgD⁺ naïve B cells (NBCs), CD19⁺CD38⁺IgD⁺ & IgD^- B_GC-cells, CD19⁺CD38⁺⁺IgD^- plasmablasts (PBs), and CD19⁺CD38^-IgD^-CD27⁺ memory B cells (MBCs) (one-way Anova & Kruskal-Wallis multiple comparisons test). (D) The proportion of CD23-positive cells in CXCR4^hiCD83^lo DZ B_GC-cells and CXCR4^loCD83^hi LZ B_GC-cells in tonsils and rLNs. (E) Flow cytometry analysis of KI67, IL4RA and CCR6 in tonsil CD23⁺ and CD23^- LZ B_GC-cells. Results are expressed as the relative mean fluorescence intensity (rMFI) or the percentage of positive cells (*P ≤ .05; "ns" for non significant; Mann-Whitney test).