Figure 5
Bifidobacterium infantis limits Salmonella typhimurium- and flagellin-induced CCL20 secretion. (a) Confluent HT-29 monolayers were pre-treated for 2 hr with 1 × 107/ml live B. infantis or Lactobacillus salivarius, or an equivalent dose of formalin-killed B. infantis prior to infection with S. typhimurium. CCL20 levels were measured 6 hr after infection. Both live and formalin-killed B. infantis restrained S. typhimurium induced CCL20 secretion (*P < 0.05 compared with S. typhimurium- infected HT-29 cells). The data are expressed as pg/ml CCL20 protein and represent the mean ± standard error (n = 8 independent experiments). (b) Confluent HT-29 monolayers were pre-treated for 2 hr with live B. infantis at doses of 1 × 105, 1 × 106, or 1 × 107 colony-forming units/ml (left panel) or 1 × 107/ml formalin-killed B. infantis (right panel). Subsequently, cells were treated with 0.5 μg/ml flagellin for 6 hr. Pre-treatment with 1 × 107 live and formalin-killed significantly inhibited flagellin-induced CCL20 secretion (*P < 0.05 relative to flagellin-treated HT-29 cells). The data are expressed as CCL20 protein levels relative to flagellin-treated cells and represent the mean ± standard error (n = 7 independent experiments).