Endocytosis of commensal antigens by intestinal epithelial cells regulates mucosal T cell homeostasis

Commensal bacteria influence host physiology, without invading host tissues. We show that proteins from segmented filamentous bacteria (SFB) are transferred into intestinal epithelial cells (IECs) through adhesion-directed endocytosis that is distinct from the clathrin-dependent endocytosis of invasive pathogens. This process transfers microbial cell wall–associated proteins, including an antigen that stimulates mucosal T helper 17 (T_H17) cell differentiation, into the cytosol of IECs in a cell division control protein 42 homolog (CDC42)–dependent manner. Removal of CDC42 activity in vivo led to disruption of endocytosis induced by SFB and decreased epithelial antigen acquisition, with consequent loss of mucosal T_H17 cells. Our findings demonstrate direct communication between a resident gut microbe and the host and show that under physiological conditions, IECs acquire antigens from commensal bacteria for generation of T cell responses to the resident microbiota

Regulation of the fructose transporter GLUT5 in health and disease

Fructose is now such an important component of human diets that increasing attention is being focused on the fructose transporter GLUT5. In this review, we describe the regulation of GLUT5 not only in the intestine and testis, where it was first discovered, but also in the kidney, skeletal muscle, fat tissue, and brain where increasing numbers of cell types have been found to have GLUT5. GLUT5 expression levels and fructose uptake rates are also significantly affected by diabetes, hypertension, obesity, and inflammation and seem to be induced during carcinogenesis, particularly in the mammary glands. We end by highlighting research areas that should yield information needed to better understand the role of GLUT5 during normal development, metabolic disturbances, and cancer

Sugar and amino acid transport in fish intestine

1. Morphological properties of fish intestines vary with diet. Carnivores have short guts with highly elaborate mucosal folding in the upper intestines; herbivores have long guts which appear structurally uniform from stomach to rectum. 2. Brush border membranes of many fish intestines display at least two transport processes for each organic solute, one an Na+-dependent, saturable carrier mechanism, and the other a non-saturable influx pathway which may be simple diffusion. 3. Intestinal epithelial cells from freshwater fish can accumulate nutrients to concentrations in excess of those in the gut lumen; those of marine fish can not. 4. Net transepithelial nutrient transport in upper intestine is greater in freshwater fish than in marine forms as a result of considerable solute backflux from epithelium to lumen in the latter. 5. In many fish the lower intestine displays a significant net transmural flux of nutrients that may contribute to total organic solute absorption. 6. Intestines of freshwater fish have a serosa positive (relative to mucosa) electrical potential difference; marine fish display a negative serosa. 7. Addition of organic solutes to intestines of freshwater fish hyperpolarizes the electrically positive serosa; in marine forms a depolarization of the serosa negative potential occurs. In both cases this appears due to increased net transmural sodium transport coupled to net nutrient flow

Osmotic, total protein and chloride regulation in Penaeus monodon

Abstract only.The osmotic, total protein and chloride ion regulation in two size groups (10 and 30 g) of Penaeus monodon Fabricius was investigated. Preliminary experiments showed that osmolality, total protein and chloride concentrations tend to become stable 24 to 36 hours after molting.Thus,hemolymph values 36 to 240 hours after sampling were not significantly different from each other. Based on these results, only 36 hours (or more) postmolt animals were sampled after transfer from control (32 ppt) to five test salinities (8, 16, 24, 32 and 40 ppt). Hemolymph samples were then taken 1, 2, 3, 5, 7 and 10 days after transfer. Results showed that in general, osmolality, total protein and chloride concentrations in the hemolymph did not vary with time within the same salinity.Both sizes exhibited hyperosmotic and hyperionic regulation in lower salinities and hypoosmotic and hypoionic regulation in higher salinities. The isosmotic values obtained were approximately 676 to 720 mOsm (24 to 28.8 ppt) for the 10 g, and 724 to 792 mOsm (26 to 28.5 ppt) for the 30 g size group. For chloride, the isoionic values ranged from 324 to 339 mM in 10 g prawns. Slopes of the regression lines of hemolymph osmolality versus salinity in 10 g prawns were not significantly different from slopes of similar regression lines in 30 g prawns. These results suggest that the ability to regulate osmotic and total protein concentration in the hemolymph is similar in the two size groups

Development of the digestive tract of milkfish, Chanos chanos (Forsskal): Histology and histochemistry

SEAFDEC Aquaculture Department Contribution No. 192.The digestive tract of the newly hatched milkfish larva is a simple undifferentiated tube. Three days after hatching, differentiation of the esophagus begins with development of mucous-secreting cells. At this time, the intestine can be distinguished from the anterior portion of the digestive tract by its tall columnar cells with centrally located nuclei and brush border with cytoplasmic projections. After 14 days, mucosal folds develop in the esophagus. In 21-day-old larvae, the stomach differentiates into the cardiac and pyloric regions while goblet cells start to develop in the intestine. In fish undergoing metamorphosis (≥ 42 days old), the mucosal cells of the cardiac stomach develop into two distinct cell types: the columnar cells which make up the folds nearest the lumen, and the cuboidal cells which constitute the gastric glands. The cardiac stomach is the only region in the digestive tract where mucus secretion is not acidic. From 3-day-old larvae up to the older stages, alkaline phosphatase is localized only at the brush border of the intestinal epithelial cells. Aminopeptidase is also found only in the brush border of enterocytes, but only in 21-day and older milkfish. Intestinal esterases are present not only in the brush border but are also diffusely distributed in the cytoplasm of enterocytes of 3-day or older fish. Esterase is also found in both the columnar and gland cells of the cardiac stomach, but only in postmetamorphic (60-day or older) fish. These morphological and histochemical changes of the gut seem to parallel dietary and habitat shifts throughout development, which encompasses life stages spent in pelagic, coastal or inland waters

Digestibility in milkfish, Chanos chanos (Forsskal): Effects of protein source, fish size and salinity

SEAFDEC Aquaculture Department Contribution No. 181.The true digestibility of casein, gelatin, fish meal, defatted soybean meal and Leucaena leucocephala leaf meal was measured in 60- and 175-g milkfish (Chanos chanos Forsskal) in fresh- and seawater. The diets contained 45% of these feedstuffs and 1.3% of the indicator substance, chromic oxide. The intestinal dissection method was used to collect fecal material. Results showed that the length of time between initial feeding and fish sacrifice did not significantly affect digestibility. Gelatin was the most digestible (90–98%) protein, regardless of size. Casein, defatted soybean meal and fish meal were moderately digestible (50–90%) and digestibility coefficients tended to increase as a function of fish size. L. leucocephala was the least digestible (−10–40%). The digestibility of most of these feedstuffs was less in the anterior than in the posterior intestine, and tended to be lower in seawater than in freshwater. Rate of food movement was similar in both size groups, but was significantly faster when milkfish were in seawater rather than in freshwater. The effect of salinity on digestibility may in part be due to food motility changes necessitated by alterations in osmoregulatory processes when fish are in seawater