IL-6 affects the extent of naïve T-cell costimulation by CD81. Total CD4 T cells (Right) and naïve CD4 T cells isolated from the same individual were cultured in the presence of anti CD3 (0.1 μg/mL), anti-CD81 (5A6) and anti-CD28 mAbs, as indicated, each at a concentration of 2.5 μg/mL and in the presence of the indicated concentrations of IL-6, the expression of CD69 was analyzed after 22 h. The cells were stained for expression of CD45RO, CD62L, CD4, and CD69 after 22 h and analyzed by flow cytometry. Shown is CD69 expression on gated naïve and memory subsets. Data are representative of three independent experiments.