FIG. 5.
Frequency of LLO-specific CD8 and CD4 T cells in spleens of mice orally immunized with 5 × 109 CFU of nontransformed Y. pseudotuberculosis yopK-null mutant strain pIB155 or of pIB155 expressing a hybrid YopE/LLO protein encoded by the indicated plasmid. Spleens from mice infected with L. monocytogenes were used as controls. The frequency of LLO-specific T cells in the spleen of each mouse was determined by ELISPOT assay as described in Materials and Methods. The frequency of cells reactive with LLO91-99 (filled bars) or LLO190-201 (open bars) is shown as the number of reactive cells per 105 splenocytes. The dotted line at 0.2 × 10−5 indicates the detection limit of the ELISPOT assay. The standard deviation of three cultures from 12 individual mice per group is indicated.