Resistant starch (RS) is starch and products of its small intestinal digestion that enter the large bowel. It occurs for various reasons including chemical structure, cooking of food, chemical modification, and food mastication. Human colonic bacteria ferment RS and nonstarch polysaccharides (NSP; major components of dietary fiber) to short-chain fatty acids (SCFA), mainly acetate, propionate, and butyrate. SCFA stimulate colonic blood flow and fluid and electrolyte uptake. Butyrate is a preferred substrate for colonocytes and appears to promote a normal phenotype in these cells. Fermentation of some RS types favors butyrate production. Measurement of colonic fermentation in humans is difficult, and indirect measures (e.g., fecal samples) or animal models have been used. Of the latter, rodents appear to be of limited value, and pigs or dogs are preferable. RS is less effective than NSP in stool bulking, but epidemiological data suggest that it is more protective against colorectal cancer, possibly via butyrate. RS is a prebiotic, but knowledge of its other interactions with the microflora is limited. The contribution of RS to fermentation and colonic physiology seems to be greater than that of NSP. However, the lack of a generally accepted analytical procedure that accommodates the major influences on RS means this is yet to be established.

Short-Chain Fatty Acids and Human Colonic Function: Roles of Resistant Starch and Nonstarch Polysaccharides

To maintain immune homeostasis, the intestinal immune system has evolved redundant regulatory strategies. In this regard, the gut is home to a large number of regulatory T (T reg) cells, including the Foxp3+ T reg cell. Therefore, we hypothesized that the gut environment preferentially supports extrathymic T reg cell development. We show that peripheral conversion of CD4+ T cells to T reg cells occurs primarily in gut-associated lymphoid tissue (GALT) after oral exposure to antigen and in a lymphopenic environment. Dendritic cells (DCs) purified from the lamina propria (Lp; LpDCs) of the small intestine were found to promote a high level of T reg cell conversion relative to lymphoid organ–derived DCs. This enhanced conversion by LpDCs was dependent on TGF-β and retinoic acid (RA), which is a vitamin A metabolite highly expressed in GALT. Together, these data demonstrate that the intestinal immune system has evolved a self-contained strategy to promote T reg cell neoconversion.

/pdf/small-intestine-lamina-propria-dendritic-cells-promote-de-jachbvfx4i.pdf

Small intestine lamina propria dendritic cells promote de novo generation of Foxp3 T reg cells via retinoic acid

The intestinal immune system must elicit robust immunity against harmful pathogens but must also restrain immune responses directed against commensal microbes and dietary antigens. The mechanisms that maintain this dichotomy are poorly understood. Here we describe a population of CD11b+F4/80+CD11c- macrophages in the lamina propria that expressed several anti-inflammatory molecules, including interleukin 10 (IL-10), but little or no proinflammatory cytokines, even after stimulation with Toll-like receptor ligands. These macrophages induced, by a mechanism dependent on IL-10, retinoic acid and exogenous transforming growth factor-beta, the differentiation of Foxp3+ regulatory T cells. In contrast, lamina propria CD11b+ dendritic cells elicited IL-17 production. This IL-17 production was suppressed by lamina propria macrophages, indicating that a dynamic interaction between these subsets may influence the balance between immune activation and tolerance.

Lamina propria macrophages and dendritic cells differentially induce regulatory and interleukin 17-producing T cell responses.

A T helper type 1 (Th1)-mediated colitis with similarities to inflammatory bowel disease in humans developed in severe combined immunodeficiency mice reconstituted with CD45RB(high) CD4+ splenic T cells and could be prevented by cotransfer of CD45RB(low) CD4+ T cells. Inhibition of this Th1 response by the CD45RB(low) T cell population could be reversed in vivo by an anti-transforming growth factor (TGF) beta antibody. Interleukin (IL) 4 was not required for either the differentiation of function of protective cells as CD45RB(low) CD4+ cells from IL-4-deficient mice were fully effective. These results identify a subpopulation of peripheral CD4+ cells and TGF-beta as critical components of the natural immune regulatory mechanism, which prevents the development of pathogenic Th1 responses in the gut, and suggests that this immunoregulatory population is distinct from Th2 cells.

https://rupress.org/jem/article-pdf/183/6/2669/1108228/2669.pdf

A critical role for transforming growth factor-beta but not interleukin 4 in the suppression of T helper type 1-mediated colitis by CD45RB(low) CD4+ T cells.

Surviving a given infection requires the generation of a controlled immune response. Failure to establish or restore homeostatic conditions during or following the onset of an infection can lead to tissue damage. Investigation of the immunoregulatory network that arises in response to the infectious process or that is induced by the pathogen itself should provide insight into therapeutic approaches for the control of infection and any subsequent immunopathology. In this Review, I discuss current hypotheses and points of polemic associated with the origin, mode of action and antigen specificity of the various populations of regulatory T cells that arise during infection.

Regulatory T cells and infection: a dangerous necessity

Selected G1 events associated with butyrate-induced differentiation were examined in HT-29 colon adenocarcinoma cells. [3H]Thymidine incorporation by HT-29 cells was decreased to 40% of control levels by treatment with 5 mM butyrate for 24 h, and cell numbers decreased to 21% of control levels after 48 h of treatment. Cells released from butyrate arrest entered S phase approximately 24 h after release, and serum-deprived HT-29 cells escaped growth inhibition if butyrate was added 8 h or more after serum restimulation. Northern analysis of RNA isolated from rapidly growing HT-29 cells showed a marked induction of alkaline phosphatase mRNA expression within 12 h of treatment with 5 mM butyrate. The appearance of alkaline phosphatase mRNA was temporally associated with a 5-fold increase in expression of transforming growth factor beta 1 (TGF-beta 1) mRNA. Expression of the nuclear protooncogene c-myc began to decrease 30 min after treatment with butyrate and was decreased 4.5-fold 4 h after treatment; however, expression of other immediate-early genes (nup/475 and zif/268) was not significantly affected. Histochemical staining of HT-29 monolayers showed that no cells were positive for alkaline phosphatase protein prior to treatment, and 90% were positive 48 h after treatment. TGF-beta 1 and TGF-beta 2 had no effect on HT-29 cell growth. TGF-beta 1 did not induce alkaline phosphatase mRNA or histochemical positivity. These data indicate that butyrate arrests HT-29 cell growth early in G1.(ABSTRACT TRUNCATED AT 250 WORDS)

http://cgd.aacrjournals.org/cgi/reprint/4/6/495.pdf

Butyrate Rapidly Induces Growth Inhibition and Differentiation in HT-29 Cells'

https://www.gastrojournal.org/article/0016-5085(93)90011-Z/pdf

Localization of transforming growth factor β isoforms in the normal murine small intestine and colon

Partial resection of the small intestine results in compensatory proliferation and adaptation in the remaining small intestinal mucosa. The molecular mechanisms governing the proliferative response are not known, nor has the timing of events associated with proliferation been adequately defined, particularly during the period just after resection. We designed experiments to characterize early (within 24 h) proliferative events associated with proximal intestinal resection and sought to determine the cell type that first responds to proliferative stimuli. Twenty-one day old male Sprague-Dawley rats underwent a 70% proximal intestinal resection or transection (control). Poly(A) RNA was isolated from the distal (ileal) remnants. Northern blots showed a marked induction of the immediate early genes zif-268, nup-475, and c-myc 1-3 h following resection, but not following transection. Immunohistochemical analysis of c-myc expression in ileal crypt epithelial cells showed a biphasic induction that was most marked 6 h after resection and less prominent 24 h after resection. Immunostaining with 5-bromodeoxyuridine (5-BrdU) was restricted to ileal crypt nuclei and was maximal 24 h after resection. All these events were observed in the absence of nutrient intake. Taken together, these data show that a potent nutrient-independent stimulus for intestinal epithelial cell proliferation occurs within minutes of partial small intestinal resection and that the first targets of this stimulus are crypt epithelial cells in the residual intestine.

Ginger J. Warwick

Papers

Butyrate Rapidly Induces Growth Inhibition and Differentiation in HT-29 Cells'

Localization of transforming growth factor β isoforms in the normal murine small intestine and colon

Early proliferative events following intestinal resection in the rat.