FIG. 1.

Cross-tolerance between Ec-LPS and Pg-LPS at the cytokine induction level. THP-1 cells were pretreated for 24 h with either medium only or LPS molecules. Following removal of the culture supernatants and washing, the cells were restimulated as indicated in the figures. Ec-LPS or Pg-LPS was used at either 0.1 (A and C) or 1 (B) μg/ml. Culture supernatants were collected after overnight incubation and assayed for TNF-α (A and B) or IL-1β (C) responses. Results are presented as means ± standard deviations of triplicate determinations. Groups pretreated with medium and similarly restimulated with medium had undetectable cytokine levels at the concentration tested (1/10). Asterisks indicate groups the values of which are significantly different (P < 0.05) from those of corresponding medium only-pretreated THP-1 groups.