Background: Previous studies have demonstrated that flagellin, a component of bacterial
flagella, engages Toll-Like receptor 5 (TLR-5) causing the activation of the Myeloid Differentiation
Factor-88 (MYD-88) pathway that leads to the production of pro-inflammatory cytokines including
Tumor Necrosis Factor–alpha (TNF-α) and Interleukin-12 (IL-12). In physiological levels, cytokines
can aid in protection against infectious agents. However, excessive production of cytokines can lead to
septic shock during sepsis.
Objective: In this study, we aimed at investigating the effect of denatured flagellin on hindering the
effects induced by intact flagellin or flagellated Pseudomonas aeruginosa on the Toll-Like Receptor-5
(TLR-5) in mice.
Methods: Mouse mononuclear cells (MNCs) were cultured with intact flagellin, heat-denatured flagellin,
TLR-5 antagonist, Pseudomonas aeruginosa, and TLR-4 antagonist each alone or in combinations.
Supernatants were collected at 4 hours post incubation to assess the levels of IL-12 and TNF-α by
Enzyme-Linked ImmunoAssay (ELISA). Furthermore, groups of BALB/c mice were injected intraperitoneally
(IP) with Pseudomonas aeruginosa, LPS-RS, intact flagellin, and denatured flagellin, each
alone or in different combinations. Serum levels of IL-12 and TNF-α were measured at 2, 4, and 6
hours post injections of Pseudomonas aeruginosa or intact flagellin.
Results: Pretreatment with denatured flagellin significantly reduced the amount of TNF-α and IL-12
produced both in vitro and in vivo by intact flagellin or Pseudomonas aeruginosa.
Conclusion: Denatured flagellin suppressed the production of the pro-inflammatory cytokines induced
by intact flagellin or Pseudomonas aeruginosa both in vitro and in vivo, probably by blocking TLR5.
Denatured flagellin might be considered as an anti-septic shock agent.