Concanavalin A (ConA) reactivity (a) of CD4+ spleen T cells (day 13 of adjuvant arthritis) from preventively treated rats with anti-CD4 mAbs. Proliferation data from two individual animals of each group are expressed as means ± SEM of triplicate cultures. The corresponding arthritis score for the animals is shown in the middle. The correlation between reactivity to ConA and the severity of arthritis is shown in (b). Normals = normal, untreated rats.