TNF and influenza: The association between activation marker expression (CD69 and CD25); T-cell proliferation; T-cell cytokine secretion (IL-2 and IFN-γ); HLA-DR expression on antigen-presenting cells; cytokine secretion (TNF-α and IL-6) from LPS-stimulated PBMCs, and self-reported cold and flu incidence or severity was examined by logistic and Poisson regression, respectively.