Advisor(s)
Jennifer Pollock
Craig Maynard
Committee Member(s)
Charles Elson Iii
Laurie Harrington
Troy Randall
School
Joint Health Sciences (Interdisciplinary)
Document Type
Dissertation
Department (new version)
Joint Health Sciences
Date of Award
9-9-2024
Abstract
Flagellins belonging to bacteria from the Lachnospiraceae family are immunodom-inant antigens in inflammatory bowel disease. Flagellin, the basic unit of flagella utilized by bacteria for motility, is recognized by the host via toll-like receptor 5 (TLR5). Due to the diversity of flagellated bacteria, we investigated if this diversity results in distinct interac-tions between the bacteria and the host. Phylogenetic analysis on over 200 flagellin se-quences, primarily from Lachnospiraceae bacteria, revealed two divergent clusters we refer to as Group 1 (G1) and Group 2 (G2). In gnotobiotic mice colonized with G1 or G2 bacte-ria, both groups induce colonic interleukin 10 (IL-10)-producing peripheral T regulatory cells. To assess host response to bacteria, we administered dextran sulfate sodium in the drinking water for 5 days to disrupt the mucus barrier. On day 7, G2 colonized mice had an increase in the inflammatory biomarker fecal lipocalin-2 (Lcn2) and induction pro-inflammatory transcripts in isolated colonic epithelial cells. To assess the host response to flagellins, we examined TLR activation in a cell line engineered to over-express and report activation of TLR5 (HEK-Blue mTLR5 cells), and we also tested intestinal epithelial cell production (IEC) of Cxcl1 and Lcn2 by organoid-derived epithelial monolayers. G2 flagel-lin stimulation of HEK-Blue mTLR5 cells resulted in increased TLR5 activity relative to the G1 flagellin stimulation. Similarly, IECs stimulated with G2 flagellins showed an increased production of Cxcl1 and Lcn2 relative to G1 flagellins. A protein alignment of G1 and G2 flagellins revealed a hypervariable 8 amino acid sequence in the N-terminus D0 domain. We generated D0 hypervariable sequence swapped (hvs-swap) G1 and G2 flagellins. Stimulation of HEK-Blue mTLR5 and IECS with G2 hvs-swap flagellins resulted in de-creased TLR5 activity and IEC production of Cxcl1 and Lcn2 relative to the native G2 fla-gellin. Conversely, stimulation with G1 hvs-swap flagellins elicited increased TLR5 activity and IEC production of Cxcl1 and Lcn2 relative to the native G1 flagellins. These findings demonstrate two divergent groups of commensal bacteria based on the diversity of the fla-gellins they encode. These two groups differentially elicit pro-inflammatory host responses via the ability of a variable motif within flagellin to activate TLR5.
ProQuest ID
Recommended Citation
Jennings, Melissa Simone, "Phylogenetic Diversity Of Flagellin Differentiates Commensal Gut Bacteria That Induce Distinct Intestinal Epithelial Cell Responses" (2024). All ETDs from UAB. 7575.
https://digitalcommons.library.uab.edu/etd-collection/7575
