FIG. 3.

AB₅ toxins inhibit, whereas their B pentamers promote, IL-8 induction. THP-1 cells were pretreated for 1 h with medium only or with 2-μg/ml concentrations of LT-IIa, LT-IIb, CT, or their respective B pentamers. The cells were subsequently incubated for an additional 16 h with 1 μg of Ec-LPS/ml (A) or were left without further treatment (B). The insert summarizes the results of an independent experiment in which THP-1 cells were incubated for 16 h with medium only or with B pentamers in the absence or presence of 10 μg of polymyxin B (PMB)/ml. Induction of IL-8 release in culture supernatants was assayed by ELISA, and data shown are means ± standard deviations of triplicate determinations. (A) Statistically significant (P < 0.05) inhibition or enhancement of LPS-induced IL-8 release is indicated by an asterisk or a black circle, respectively. (B) B-pentamer-induced IL-8 responses that are statistically significantly (P < 0.05) higher than those corresponding to their respective holotoxins are indicated by asterisks, while IL-8 responses that are statistically significantly (P < 0.05) elevated over medium-only-treated controls are indicated by black circles.