FIG. 4.

Purified Stx1 B subunits alone do not induce IL-1β protein or mRNA production in THP-1 cells. Differentiated THP-1 cells (5 × 10⁶ cells/ml) were treated with Stx1 B subunits (400 or 800 ng/ml) for 24 h. (a) Cell-free supernatants were collected, and human IL-1β-specific ELISAs were performed to detect secreted IL-1β. Media collected from untreated cells and cells treated with Stx1 (400 ng/ml) served as negative and positive controls, respectively. Data shown are means ± standard errors of the means (error bars) from triplicate determinations of three independent experiments. Values that were significantly different (P ≤ 0.05) between unstimulated and treated cells are indicated (*). (b) Fifteen micrograms of total RNA extracted from cells treated with LPS, Stx1, Stx1 B subunits, and unstimulated cells were subjected to Northern blot analysis to detect IL-1β mRNA expression.