Fig. 4. Inclusion of adjuvant does not result in detectable increases in the total number of Tfh in circulation at d10 p.b., but alters the quantity of influenza virus-specific Tfh in the draining lymph node following challenge.

PBMC collected from newborn NHP at d10 p.b were assessed for the presence of circulating T follicular helper cells by flow cytometry. Three age-matched untreated controls were included in the PBS group to increase sample size. a Gating strategy to identify live CD4⁺ T cells. Tfh were defined as CXCR5⁺ ICOS⁺ cells within this population as shown by representative data in b. c Average frequencies of Tfh as a percentage of live cells in circulation. d A separate group of vaccinated infants was challenged by infection with 1 × 10¹⁰ EID50 of PR8 divided equally between the intranasal and intratracheal routes. On d14 p.c., tracheobronchial lymph nodes were isolated. IL-21 production was induced by culture in the presence of pooled peptides from the NA, HA, M1, and NP proteins (0.1 µg/ml for each peptide) for 48 h. IPR8 + m229 n = 4, adjuvanted vaccine groups n = 5. Statistical significance was determined by ordinary one-way ANOVA with uncorrected Fisher’s LSD test for multiple comparisons. *p < 0.05, **p < 0.01.