Figure 7.

Neutralising antibody titres correlate with Tfh cell subset frequencies after yellow fever vaccination. (a–f) The level of neutralising antibodies at day 28 after YF‐17D vaccination was measured by focus reduction neutralisation tests and is shown as log₁₀(ED₅₀) representing the dilution of serum called effective dose (ED) leading to 50% reduction of foci in the test. The ED50 was correlated with the frequencies of (a) Tfh1, (b) Tfh17, (c) activated CD38⁺ Tfh1 and (d) activated CD38⁺ Tfh17 cells on days 14 and 28 after vaccination, as well as (e) cTfh1 cells and (f) cTfh17 cells expressing different combinations of the activation markers ICOS, CD38 and PD‐1 on day 14 post‐vaccination as determined by flow cytometry. Spearman's rank correlation coefficients were used to calculate correlations, and r‐ and P‐values are indicated. Linear regressions are shown as lines and each dot represents one donor (n = 28).