FIG 3.

High prevaccine serological Ab titers dampen the B cell response. (A and B) Correlation between the proportion of influenza virus-specific plasmablasts generated 7 days after vaccination with the 2012-2013 or 2013-2014 TIV and memory B cells specific for the indicated strain detected 12 to 14 days after vaccination (A) or the fold increase in serum Abs levels (upper panels) or fold change (FC) in serum HAI titer (lower panels) between day 0 and day 14/21 after vaccination (B). Plasmablasts specific to the indicated viral strain rHA or whole virus was determined by ELISPOT assay 7 days after vaccination by placing freshly isolated PBMCs on an antigen-coated ELISPOT assay plate overnight. To detect influenza virus specificity of memory B cells, PBMCs were incubated for 5 days with B cell mitogens to induce differentiation of memory B cells into antibody-secreting cells. Activated cells were then placed on an antigen-coated ELISPOT assay plate overnight. Shown is the percentage of total vaccine-positive IgG⁺ IgA⁺ antibody-secreting cells specific for the indicated influenza virus strain (A) or the total number of strain-specific antibody-secreting B cells per 1 × 10⁶ PBMCs (B). (C) Correlation between percentage of influenza virus strain-specific plasmablasts induced by vaccination and the percentage of memory cells (Mem) specific to that strain present just before vaccination determined as described for panel A. (D) Correlation between the total number of strain-specific antibody-secreting B cells per 1 × 10⁶ PBMCs and serum Ab EC₅₀ present on the day of vaccination (day 0). The Spearman r (rs) value for non-Gaussian distributions and corresponding P value were used to determine the degree of correlation for all analyses. d, day; PB, plasmablasts.