Figure 5.

Mice generate impaired influenza virus stalk-specific B cell responses in the absence of follicular regulatory CD4⁺ T cells in a sequential vaccination model with antigenically diverse antigens. Analysis of the stalk-specific B cell response in Bcl6^f/f Foxp3-Cre and Bcl6^f/f mice following multiple boosts in an influenza virus sequential vaccination model. (A) Schematic of the sequential vaccination model. (B) Quantification of stalk-specific IgG antibody titers as determined by ELISA using chimeric HA cH11/1 as coating substrate at 40 d following the first boost (top) and 40 d following the second boost (bottom). (C) Left: Quantification of stalk-specific ASCs in the bone marrow compartment from Bcl6^f/f or Bcl6^f/f Foxp3-Cre mice at 42 d following the second boost. Right: Quantification of the total number of bone marrow cells in each mouse. (D) Antibody response against the H1N1 head domain in Bcl6^f/f Foxp3-Cre and Bcl6^f/f mice measured by influenza hemagglutination inhibition assay following sequential vaccination. Statistical analyses were performed using the unpaired two-tailed Student’s t test (*, P < 0.05). Data for A–C are from one experiment representative of two experiments with five to seven mice per group performed at various time points following sequential vaccination with diverse group 1 influenza viruses. Data for D are pooled from two independent experiments with five to seven mice per group following sequential vaccination. AUC, area under the curve; n.s., not significant.