Age dependent differences in the kinetics of γδ T cells after influenza vaccination

Abstract

Immunosenescence is a hallmark of the aging immune system and is considered the main cause of a reduced vaccine efficacy in the elderly. Although γδ T cells can become activated by recombinant influenza hemagglutinin, their age-related immunocompetence during a virus-induced immune response has so far not been investigated. In this study we evaluate the kinetics of γδ T cells after vaccination with the trivalent 2011/2012 northern hemisphere seasonal influenza vaccine. We applied multi-parametric flow cytometry to a cohort of 21 young (19-30 years) and 23 elderly (53-67 years) healthy individuals. Activated and proliferating γδ T cells, as identified by CD38 and Ki67 expression, were quantified on the days 0, 3, 7, 10, 14, 17, and 21. We observed a significantly lower number of activated and proliferating γδ T cells at baseline and following vaccination in elderly as compared to young individuals. The kinetics changes of activated γδ T cells were much stronger in the young, while corresponding changes in the elderly occurred slower. In addition, we observed an association between day 21 HAI titers of influenza A and the frequencies of Ki67+ γδ T cells at day 7 in the young. In conclusion, aging induces alterations of the γδ T cell response that might have negative implications for vaccination efficacy.

Fig 1. Baseline activation of γδ T cells changes with age.

A) The gating hierarchy of the analyzed populations and their common CD3⁺ ancestor. Relative frequencies of γδTCR⁺ subsets (B) and their absolute counts per µl blood at day 0 are shown (C); total CD38⁺ among γδ T cells (D and E) cells, and total Ki67⁺ among γδ T cells (F and G). The box represents the 25^th, 50^th, and 75^th percentile and the whiskers represent the range of the observations excluding outliers. Each point signifies a single donor. NS indicate not significant, asterisks indicate p-values (** p < 0.01; * p < 0.05) after comparison with Student's t-test.

Fig 2. Activation status changes rapidly after vaccination.

A) Total Ki67⁺ among γδTCR⁺. B) Proportionality in the segments day 0 to 3 and C) day 7 to day 21. D) CD38⁺Ki67⁺ among γδTCR⁺. E) Proportionality in the segments day 0 to 3, and F) day 7 to day 21. The box in figures A and D represents the 25^th, 50^th, and 75^th percentile and the whiskers the range excluding outliers (open circles). Asterisks indicate p-values (*** < 0.001; ** p < 0.01; * p < 0.05) after comparison with Student's t-test. p-values were corrected by the FDR method and only significant differences are shown. The two age groups in figures B, C, E, and F are slightly offset to the day of measurement to improve the visualization. Each point represents a single donor. The formula y = β + αx was fitted in B and E. The formula y = β + α/x was fitted in C and F. The given values indicate the proportionality constant α.

Fig 3. Dynamic changes of activated γδ T cells.

A) Kinetics of absolute count of total CD38⁺ after vaccination. B) Linear fit for day 0 to 6, C) day 7 to 10, D) day 10 to 17, and E) day 17 to 21. F) Kinetics of absolute count of CD38⁺Ki67^– after vaccination. G) Linear fit for day 0 to 6, H) day 7 to 10, I) day 10 to 17, and J) day 17 to 21. The box in figures A and F represents the 25^th, 50^th, and 75^th percentile and the whiskers the range excluding outliers (open circles). Asterisks indicate p-values (*** < 0.001; ** p < 0.01; * p < 0.05) after comparison with Student's t-test. p-values were corrected by the FDR method and only significant differences are shown. The two age groups in figures B-E and in G-J are slightly offset to the day of measurement to improve the visualization. Each point represents a single donor. The formula y = β + αx was fitted in B-E and G-J. The given values indicate the proportionality constant α.

Fig 4. Proliferation level associates with vaccination titer in the young.

Day 21 HAI titers of A/California/7/2009 (H1N1) and A/Perth/16/2009 (H3N2) compared to A-B) the frequency of total Ki67⁺ among γδTCR⁺ or C-D) the frequency of CD38⁺Ki67⁺ among γδTCR⁺ at day 3 and 7. Correlation by the Spearman rank method. Each point indicates a donor.