FIG. 4.

Antigen-presenting cells are required for T-cell proliferation to exoenzyme S. PBMC or purified T cells with and without accessory cells (AC) were incubated with 1 μg of exoenzyme S (Exo S; A) or 10 μg of concanavalin A (Con A; B) per ml. Cultures stimulated with concanavalin A were harvested on day 3, while cultures stimulated with exoenzyme S were harvested on day 7. The experiment was repeated three times with similar results. ∗, P < 0.05 calculated by ANOVA compared with the corresponding unstimulated group; NS, nonsignificant difference compared with the corresponding unstimulated group.