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

Immunosenescence is a hallmark of the aging immune system and is considered the main cause of a reduced vaccine efficacy in the elderly. Although $\gamma \delta$ 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 $\gamma \delta$ 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 $\gamma \delta$ 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 $\gamma \delta$ T cells at baseline and following vaccination in elderly as compared to young individuals. The kinetics changes of activated $\gamma \delta$ 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 $Ki67^{+}$ $\gamma \delta$ T cells at day 7 in the young. In conclusion, aging induces alterations of the $\gamma \delta$ T cell response that might have negative implications for vaccination efficacy