Bacterial flagellin is a dominant, stable innate immune activator in the gastrointestinal contents of mice and rats

ABSTRACT

Intestinal contents comprise the largest repository of immunogenic ligands of microbial origin. We undertook this study to assess the predominant microbe-associated molecular patterns (MAMPs) present therein and the receptors) that mediate the innate immune responses to them. Here, we demonstrated that intestinal contents from conventional, but not germ-free, mice and rats triggered robust innate immune responses in vitro and in vivo. Such immune responses were abrogated in the absence of either myeloid differentiation factor 88 (MyD88) or Toll-like receptor (TLR) 5, but not TLR4, suggesting that the stimuli was flagellin (i.e., protein subunit of flagella that drives bacterial motility). Accordingly, pre-treating intestinal extracts with proteinase, thereby degrading flagellin, was sufficient to block their ability to activate innate immune responses. Taken together, this work serves to underscore flagellin as a major, heat-stable and bioactive MAMP in the intestinal content that confers this milieu strong potential to trigger innate immune responses.

KEYWORDS:

• Gut microbiota
• LPS
• MyD88
• toll-like Receptor-5
• toll-like Receptor-4
• cytokines
• IL-10

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary data

Supplemental data for this article can be accessed online at https://doi.org/10.1080/19490976.2023.2185031

Competing interests

The authors declare that they have no competing interests.

Data availability statement

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

Author contributions

M.V-K for conception and design. V.R.B., B.S.Y., R.M.G., P.S. for acquisition of data. V.R.B., B.S.Y., and P.S. for analysis and interpretation of data. M.V-K, B.S.Y and A.T.G for drafting the manuscript. B.S.Y., B.J., A.T.G., and M.V-K for critical appraisal of results. M.V-K, V.R.B., B.S.Y., R.M.G, P.S., B.J., and A.T.G. for final approval of the version to be published.

Additional information

Funding

The work was supported by the National Institutes of Health [R01 DK083890 to A.T.G.]; National Institutes of Health [R01 CA219144 to M.V-K.]; National Institutes of Health [R01 DK099071 to A.T.G.]; American Heart Association [855256 to P.S.]; National Cancer Institute [F31CA260842 to R.M.G.]; American Heart Association [831112 to B.S.Y.]; Crohn’s and Colitis Foundation [854385 to P.S.]