T cells fail to respond to HA. Purified T cells (B-cell depleted) from normal C57BL/6 mice were cultured in the presence of anti-CD3 (1:200), LPS (50 μg/mL), HA (0.5 mg/mL), or KM201(1:2), or medium alone (control). Cell proliferation was measured as described previously in the legend to Fig 1.