Page 665 - Veterinary Immunology, 10th Edition

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FIG. 21.8 The role of clostridial clusters in promoting both local
and systemic Treg activity.

In addition to the Clostridia, the capsular polysaccharide-A of
Bacteroides fragilis triggers IL-10 production through the TLR2-
MyD88 pathway. Numerous Clostridia species can trigger IL-10

production by a non-MyD88 pathway involving TGF-β production
by intestinal epithelial cells. Other mechanisms such as
desensitization of TLRs to bacterial PAMPs and bacterial
stimulation of IL-10 and IL-2 production by Treg cells also help

minimize inflammation.
Additionally, some commensal bacteria actively suppress
intestinal inflammation. For example, Lactobacilli and Bacteroides
inhibit the innate signaling pathways triggered by TLRs and NLRs.

A common commensal, Bacteroides thetaiotaomicron inhibits NF-κB
signaling and intestinal lactobacilli prevent degradation of the NF-
κB inhibitor IκB.
The presence of Clostridial clusters in the colon also results in an

increase in the numbers of IL-10 producing Treg cells in distant
tissues such as the spleen and lung, and they play a role in
inhibiting allergic responses. Thus T cells educated by commensal
bacteria may emigrate from the gut to remote tissues and determine

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