Page 673 - Veterinary Immunology, 10th Edition

Enterocytes can sense this tight attachment (Fig. 21.11). The
VetBooks.ir mechanism by which this affects enterocytes is unclear, but SFBs

cause enterocytes to produce serum amyloid A (SAA) (Chapter 7).
The SAA acts as a cytokine and stimulates IL-23 production by

macrophages leading to ILC3 secretion of IL-22 and -17. This in turn
triggers development of Th17 cells. Lamina propria macrophages
and dendritic cells can also detect SFB-derived molecules through
their TLRs and produce IL-23 and TGF-β, promoting further Th17

cell differentiation. As a result the T cells differentiate into RORγt-
expressing Th17 cells. Th17 cells in turn regulate the abundance of
SFBs by promoting the production of antibacterial peptides such as
β-defensins, lipocalins, and calprotectin by enterocytes.

FIG. 21.10 The role of segmented filamentous bacteria and
Clostridia in regulating T cell subset formation and in controlling
intestinal inflammation. Bacillus fragilis and the clostridia activate
dendritic cells by stimulating production of TGF-β retinoic acid and

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