Pathogen species-specific induction of NF-κB activity in different cells. Cells were transiently transfected with the NF-κB reporter plasmid and stimulated with 30 µg/mL of protein from preparations of the heat-killed pathogens, as indicated. The increase in NF-κB activity was measured from cell lysates sampled 24 h after the challenge. Mean values from two independent experiments, each assayed in triplicate. *, P < 0.05; ***, P < 0.001.