Flagellin

Flagellin is a structural component of bacterial flagella produced by pathogenic, symbiotic, and neutral bacteria

Silent flagellin proteins were present in human stool. These silent flagellins were mainly produced by the abundant gut bacteria Lachnospiraceae.
Clasen et al. 2023 Science Immunology 8(79): https://doi.org/10.1126/sciimmunol.abq7001

Flagellins from commensals can be tolerated by the host, while those from pathobionts can trigger reactions in the host.
Clasen et al. 2023 Science Immunology 8(79): https://doi.org/10.1126/sciimmunol.abq7001

Flagellin and Anti-CD3 monoclonal antibody, two distinct immune stimuli, induced similar transcriptional profiles. This suggests that Commensal Bacteria / Commensalism detect common effectors or activate shared pathways when facing different host responses.
Becattini et al. 2021 Cell Host & Microbe 29: 378-393

Flagellins, widely distributed in various bacterial taxa, have strong immunostimulatory effects
Zheng et al. 2020c Cell Res. 30: 492-506

Bacterial flagellin serves as an antigen to modulate the host immune responses.
Lodes et al. 2004 J Clin Invest 113(9): 1296-306
Mutlu et al. 2016 Gastroenterology 150(4, Supplement 1): S778

Flagellin is agonist of TLR-5 receptors upregulating the expression of Regenerating Islet-Derived Protein 3 Gamma / Regenerating Islet-Derived Protein III-Gamma (REG3G), regulating cell proliferation, the mucosal barrier function and multiple cellular inflammatory pathways by activating the innate immune system
Arthur et al. 2011
Elinav et al. 2013
Li et al. 2014b
Tian et al. 2015
Lewis et al. 2016

The interaction between flagellin and intestinal epithelium was mainly studied on E. coli Nissle 1917 (EcN)
Schlee et al. 2007 Infect Immun. 75: 2399-407

see also:
Defending & Pathogens / Pathobionts / Pathogenic Bacteria
Flagellin & Toll-like receptor 5 (TLR-5)