Low signal strength through the TCR/CD3 complex favors Th17 cells only in the presence of anti-CD28. Human CD4⁺ T cells were cultured for 6 days at a 1:10 bead:CD4⁺ T cell ratio. Beads were loaded with decreasing concentrations (40-2.5 μg/mL) of anti-CD3 ± 10 μg/mL anti-CD28. Cells were restimulated with PMA/ionomycin for 5 hours, and expression of IL-17 and IFN-γ was determined by intracellular flow cytometry. Results are representative of 3 independent experiments.