Figure 4.

B cell antigen presentation preferentially drives T_FH differentiation in response to viral infection. B-MHCII and MHCII KO mice received 1×10⁷ CD4⁺ T cells from C57/BL6 mice 7–14 days prior to infection to reconstitute the CD4⁺ T cell compartment. 1×10⁴ SMARTA transgenic CD4⁺ T cells were transferred to WT and B-MHCII mice and the mice were infected with LCMV Armstrong one day later. Splenocytes were analyzed on day 8 post infection. (A) Representative FACS plots of CD19⁻ TCRβ⁺ CD4⁺ SMARTA cells to identify CXCR5⁺ PD-1⁺ T_FH cells. (B) Percentage of SMARTA cells in WT and B-MHCII mice that are CXCR5⁺ PD-1⁺ T_FH cells. (C) Total number of splenic SMARTA T_FH cells in WT, B-MHCII and MHCII KO mice. (D) Histogram overlay of Bcl6 expression by CXCR5⁺ PD-1⁺ SMARTA T_FH cells. (E) Relative expression of IL-21 mRNA in sorted CXCR5⁺ PD-1⁺ SMARTA cells. (F) Total number of CD19⁼ B220⁺ IgD^lo GL-7⁺ GC B cells. (G) Measurement of LCMV specific IgG in the serum on d8 p.i., compared to uninfected C57/BL6 mice. * denotes a p value of < 0.05, ** denotes a p value of <0.01 and *** denotes a p value of <0.001 calculated using Student’s t test. Bar graphs show mean ± SEM. Data are representative of 2 independent experiments with 3–6 mice per group.