Page 674 - Veterinary Immunology, 10th Edition

thymic stromal lymphopoietin (TSLP). These promote the activation
VetBooks.ir to produce serum amyloid A (SAA). This stimulates dendritic cells to
of Treg cells. Segmented filamentous bacteria stimulate enterocytes

produce cytokines that generate Th17, Th1, and B cells.

FIG. 21.11 Scanning electron micrographs of segmented
filamentous bacteria in the terminal ileum of mice. (From Ivanov II,
Atarashi K, Manel N et al: Induction of intestinal Th17 cells by segmented
filamentous bacteria, Cell 139:485-498, 2009. Elsevier. With Permission.)

SFB are unique spore-forming, long filamentous Gram-positive
anaerobic commensals found in the small intestine of mammals and

birds. They do not yet have a formal scientific name. Their interim
name is “Candidatus Savagella.” (Candidatus is a term used for the
provisional name of unculturable bacteria.) They have a unique
ability to stimulate the maturation of T and B cells and especially

stimulate Th17 responses and IgA production. They can also
stimulate the upregulation of host innate defense genes,
inflammatory cytokines, and chemokines. They attach very strongly
to the enterocytes of the terminal ileum and the cells overlying

Peyer's patches, where they are in a good position to be sampled by
dendritic cells. (Most other bacteria remain within the mucus.) SFB
induce the development of germinal centers in Peyer's patches and
other intestinal lymphoid organs and increase production of IgA

and Th17 cells. In the absence of SFB, mice mount weaker IgA
responses and poorer intestinal T cell responses and recruitment of
intraepithelial lymphocytes. It is not believed that the Th17 cells are
directed against specific antigens in the SFBs; they appear to

develop polyclonally through bystander activation.

Retinoic acid.

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