Relative abilities of distinct isotypes of human major histocompatibility complex class II molecules to bind streptococcal pyrogenic exotoxin types A and B

The relative ability of distinct isotypes of human leukocyte antigen class II molecules to bind streptococcal pyrogenic exotoxins A and B (SPE A and SPE B, respectively) was investigated by a direct-binding assay with 125I-labeled toxin for SPE A and by a functional assay system measuring the accessory cell activity of human leukocyte antigen class II transfectants in toxin-induced T-cell activation for SPE A and SPE B. SPE A binding was observed in L cells transfected with DQw1 genes. By contrast, it was not detected in L cells transfected with DR2, DR4, DPw4 or DP(Cp63) genes. All the transfectants supported SPE-induced interleukin-2 production by human T cells except the DP transfectants for SPE B. Levels of accessory cell activity were low in the DP transfectants induced by stimulation with SPE A and in the DR and DP transfectants induced by SPE B. The results indicate that SPE A and SPE B bind well to DQ molecules, less well to DR molecules, and very weakly to DP molecules.