Figure 4.

Increases in CD4⁺ T-cell reactivity to hemagglutinin (HA) correlate with higher microneutralization (MN) titers. A and B, Correlation between the change in HA-specific (A) or nucleoprotein (NP)-specific (B) CD4⁺ T cells and the maximum neutralizing antibody titer measured. CD4⁺ T-cell responses with a negative change between day 14 and baseline were normalized to 0. r and P values were calculated using the Spearman rank correlation test. C and D, Subjects were subgrouped based on their CD4⁺ T-cell response to the HA (C) or NP (D) peptide pools, with a positive response defined as an increase of >20 spots in CD4⁺ T-cell reactivity. Bars represent the geometric mean MN titer, with error bars showing 95% confidence intervals. P values were calculated using the Mann–Whitney U test. Abbreviation: PBMC, peripheral blood mononuclear cell.