Fig. 3.

GrB+ CD8 T cells degranulate in response to influenza virus and the proportion of degranulating GrB+ CD8 T cells is higher in older compared to younger adults. Human PBMC stimulated for 5 days with influenza virus, A/Wyoming/03/2003 [A/H3N2], were rechallenged with the same virus in parallel (+ virus), the controls that were not rechallenged. The proportion of cells with cytolytic activity was detected by CD107b expressed on the cell surface in the process of degranulation. A, The stimulated control (not rechallenged), showed that only GrB+CD8 T cells accumulated CD107b on the cell surface while most of GrB− subset were CD107b−. Numbers indicate the percentages of CD107b+ cells in total CD8 T cells. B, GrB− CD8 T cells remained CD107b− with virus rechallenge while the GrB+ subset continued to accumulate and becomes largely CD107b+. Numbers indicate the percentages of CD107b+ cells in total CD8 T cells. C, In younger adults, virus rechallenge did not significantly change the mean percentage of CD107b+ in the GrB+CD8+ subset and this response did not change following vaccination. There was no significant increase in the mean proportion of CD107b+GrB+CD8 T cells. D, In older adults prior to vaccination, virus rechallenge was associated with a decrease in the mean percentage of CD107b+GrB+CD8+ in the total CD8 T cell subset. However, at 4-weeks post-vaccination in older adults, virus rechallenge resulted in a significant increase in the mean percentage of CD107b+GrB+CD8 subset of total CD8 T cells (N=109, p<0.01). Error bars represent standard error of the mean.