FIG. 1.

Inhibition of human PBMC proliferative responses to PHA by S. pyogenes CE prepared from the following strains: (a) M5 Smith (-•-), M5 R91/1974 (▵), M5 NCTC 8193 (○), M2 NCTC 8322 44/R64 (□), M14 NCTC (▿), and M27 NCTC 8328 (----•----) and (b) PT2110 (-▪-), M15 NCTC (▾), PT2841 (----□----), M80 (----○----), PT3875 (----▪----), and Manfredo (▴). Human PBMC (2 × 10⁶/ml were incubated in 96-well round-bottom plates with PHA (1.0 μg/ml) in the presence of a range of concentrations of streptococcal CE from various strains. After 3 days, the cells were pulsed with tritiated thymidine for the final 6 h of culture and the incorporated radioactivity was measured. Results show level of proliferation as a percentage of the proliferative response observed in the presence of 0.625 μg of each CE per ml. Maximum levels of PBMC proliferation in response to PHA (1.0 μg/ml) in the presence of 0.625 μg of each CE per ml were as follows (cpm ± SEM, n = 3): M5 Smith (6,213 ± 802), M5 R91/1974 (6,856 ± 792), M5 NCTC 8193 (5,828 ± 343), M2 NCTC 8322 44/R64 (4,866 ± 222), M14 NCTC (10,522 ± 1,665), M27 NCTC 8328 (7,644 ± 1,141), PT2110 (4,444 ± 918), M15 NCTC (9,625 ± 800), PT2841 (8,048 ± 1,096), M80 (7,654 ± 662), PT3875 (7,290 ± 988), and Manfredo (6,032 ± 331). Levels of background proliferation were not greater than 150 cpm. ∗, CE from all strains, except PT2110 and M15, significantly inhibited (P < 0.005) PBMC proliferation at concentrations of 5.0 μg/ml or higher.