In multiple studies, we have shown in PBMC that the ratio of IFNγ to interleukin (IL)-10 (IFNγ:IL10) in supernatants of stimulated PBMC and biological activity of the cytolytic mediator, granzyme B (GrB), in lysates of ex vivo influenza challenged PBMC correlate with protection against influenza illness [70, 71] and disease severity in older adults [72]. The gene discussed is IFNG; the disease is influenza.