FIG. 1.

TNF-α-like activity released by Y. enterocolitica-infected J774A.1 macrophages. J774A.1 cells were infected with various Y. enterocolitica strains at a multiplicity of 20 bacteria per cell: WT, wild-type E40; yscN, secretion mutant (S); yopB and yopD, translocation mutants (T); yopQ, yopE, yopH, yopO, yopM, and yopP, single yop mutants; yopP/P⁺⁺, yopP mutant complemented with the yopP overexpressing plasmid pMSK13. The infection procedure and the TNF-α assay were as described in Materials and Methods. Results are expressed as the percentage of the maximal response and are the mean values of three separate experiments. Error bars represent the standard deviation of the three experiments. Refer to Table 1 for the identification of the strains used.