The comparative frequency of human T cells responding to a native antigen and a synthetic peptide derived from Streptococcus mutans.

The frequency of human peripheral blood T cells responding to a 21-residue synthetic peptide (SP 21) derived from the sequence of a 3.8-kDa streptococcal antigen was estimated by limiting dilution analysis and compared with the frequency of cells responding to the native, cross-reactive 185-kDa streptococcal antigen. Frequency estimates were made by measuring both [3H]thymidine incorporation and IL 2 production in the same cell cultures. The results provided frequency estimates for SP 21-reactive cells of between 1:42 147 and 1:306 110, with a mean of 1:160 617 by [3H]thymidine incorporation, and 1:139 893 to 1:241 315 (mean 1:165 315) using the IL 2 assay. With the native 185-kDa streptococcal antigen, frequency estimates were between 1:38 393 and 1:86 142 (mean 1:169 934) according to the proliferative response and 1:22 462 and 1:100 400 (mean 1:61 189) by the IL 2 assay.