Search

The distributions of β-defensin 1 and 2 in secretory host defense system throughout respiratory tract of healthy rats were immunohistochemically investigated. In the nasal epithelium, a large number of non-ciliated and non-microvillous cells (NCs) were immunopositive for both β-defensin 1 and 2, whereas a small number of goblet cells (GCs) were immunopositive only for β-defensin 1. Beta-defensin 2-immunopositive GCs were few. In the nasal glands, a small number of acinar cells and a large number of ductal epithelial cells were immunopositive for both β-defensins. In the laryngeal and tracheal epithelia, a very few NCs and GCs were immunopositive for both β-defensins. In laryngeal and tracheal glands, a very few acinar cells and a large number of ductal epithelial cells were immunopositive for both β-defensins. In the extra-pulmonary bronchus, a small number of NCs were immunopositive for both β-defensins. A small number of GCs were immunopositive for β-defensin 1, whereas few GCs were immunopositive for β-defensin 2. From the intra-pulmonary bronchus to alveoli, a very few or no epithelial cells were immunopositive for both β-defensins. In the mucus and periciliary layers, β-defensin 1 was detected from the nose to the extra-pulmonary bronchus, whereas β-defensin 2 was weakly detected only in the nose and the larynx. These findings suggest that the secretory sources of β-defensin 1 and 2 are mainly distributed in the nasal mucosa and gradually decrease toward the caudal airway in healthy rats.

Indigenous bacteria in the alimentary tract are exposed to various bactericidal peptides and digestive enzymes, but the viability status and morphological changes of indigenous bacteria are unclear. Therefore, the present study aimed to ultrastructurally clarify the degeneration and viability status of indigenous bacteria in the rat intestine. The majority of indigenous bacteria in the ileal mucous layer possessed intact cytoplasm, but the cytoplasm of a few bacteria contained vacuoles. The vacuoles were more frequently found in bacteria of ileal chyme than in those of ileal mucous layer and were found in a large majority of bacteria in both the mucous layer and chyme throughout the large intestine. In the dividing bacteria of the mucous layer and chyme throughout the intestine, the ratio of area occupied by vacuoles was almost always less than 10%. Lysis or detachment of the cell wall in the indigenous bacteria was more frequently found in the large intestine than in the ileum, whereas bacterial remnants, such as cell walls, were distributed almost evenly throughout the intestine. In an experimental control of long-time-cultured Staphylococcus epidermidis on agar, similar vacuoles were also found, but cell-wall degeneration was never observed. From these findings, indigenous bacteria in the mucous layer were ultrastructurally confirmed to be the source of indigenous bacteria in the chyme. Furthermore, the results suggested that indigenous bacteria were more severely degenerated toward the large intestine and were probably degraded in the intestine.

A portion of the minute chylomicrons less than 75 nm in diameter are transcytosed from the extravascular tissue into the subepithelial blood capillaries (sBC) in the villous apices of the rat jejunum. However, the details of the transportation mechanism have not been clarified. In this study, the endothelial receptor involved in the transportation of minute chylomicrons into the sBC’s lumina was immunohistochemically and histoplanimetrically examined in intestinal villi of the rat jejunum. Immunopositivity for very low density lipoprotein (VLDL) receptor was detected on the luminal and basal surfaces of the endothelial cells of sBC in approximately 68% of those apices of jejunal villi that possessed numerous chylomicrons in the lamina propria, while VLDL receptor was detected on the endothelial cells of sBC in only approximately 8% of intestinal villi that possessed few or no chylomicrons in the lamina propria. No immunopositivity for LDL receptor was detected in the sBC of all intestinal villi. These findings suggest that VLDL receptor is expressed by the endothelial cells of the sBC in conjunction with the filling of the lamina propria of jejunal villi with many chylomicrons produced by the villous columnar epithelial cells and that the VLDL receptor mediates the transportation of minute chylomicrons, maybe VLDL, into the subepithelial portal blood from the extravascular tissue of the rat jejunal villi.

The hypothesis that apoptotic factors play some roles in the denucleation of erythroblasts has been confirmed by the immunohistological detection of both phosphatidylserine and thrombospondin as phagocytosis-inducing factors in general apoptotic events. Both phosphatidylserine and thrombospondin were detected on the surface of cell membrane of mature erythroblasts, while thrombospondin was also detected in more immature erythroblasts. The intensities of their immune reactions increased as the erythroids matured. During denucleation, the positivities of both phosphatidylserine and thrombospondin were restricted on the surface of the cell membrane surrounding the protruding nuclei. Thus, the apoptotic process involves denucleation of erythroblasts and phosphatidylserine, and thrombospondin acts as phagocytosis-inducing factors in the denucleation event.

The relationship between the kinetics of villous columnar epithelial cells and the expansion of colonies of indigenous bacteria from the narrow apical portions of intestinal villi was immunohistochemically and histoplanimetrically investigated in the small intestine of bromodeoxyuridine administred Wistar rats. As a result, the lifespan of villous columnar epithelial cells was slightly shorter in the distal ileum than in other portions of small intestine, accompanying the minimum height of the intestinal villi of the distal ileum in the small intestine. The migration speed of villous columnar epithelial cells was significantly decreased toward the distal small intestine. The migration speed in the distal ileum was about one-fourth of that in the duodenum. The migration speed of the villous columnar epithelial cells was greater and their lifespans were shorter in the sites with wide expansion of the indigenous bacterial colony from the narrow apical portions of the intestinal villi than that in sites with no or less expansion. Additionally, the expansion of the indigenous bacterial colony from narrow villous apices also immediately shortened the heights of the intestinal villi. These findings suggest that the migration speed of villous columnar epithelial cells might contribute to the regulation of the settlement of bacteria at the villous apices and the inevitable proliferation of indigenous bacteria at the intervillous spaces in the rat small intestine.

The spatial relationship between the distribution of indigenous bacteria (IB) and the situation of mucosal lymphatic follicles (LF) is histoplanimetrically studied in the rat alimentary tract. From the oral cavity to the nonglandular part of the stomach, IB adhered to the corneal layer of the most luminal mucosa. In the glandular part of the stomach, IB adhered only to the most luminal mucosa but not in the gastric pits. In the small intestine, IB consistently adhered around the apices of both intestinal villi and the domes, and their amounts decreased toward their basal portions. No IB entered the intestinal crypts. In the large intestine, IB consistently adhered to the most luminal mucosa. Numerous IB were suspended in the intestinal crypts of both the cecum and the proximal colon, whereas there were no IB in the crypts of the distal colon and the rectum. When IB spread over the basal portions of the intestinal villi, IB with the same morphology were detected on the neighboring LF, whereas no bacteria were detected on the neighboring LF, when IB were located in the apical to middle portions of the intestinal villi. This close relationship between the distribution of IB and mucosal LF was also observed in the large intestine. These results suggest that the most luminal mucosae are a fundamental settlement site of IB throughout the alimentary tract and that the hyperproliferation of IB's colonies might be detected by neighboring LF in the rat intestine.

The ultrastructure of epithelial responses against the membrane adhesion of indigenous bacteria was investigated in the follicle-associated epithelium (FAE) of rat small intestine. The most frequent adherence of the various morphological types of bacteria to the epithelial membranes was found at the apex of the FAE. The attachment sites were deeply invaginated, and their bottoms were deformed into a sharp cone shape. Four layers with different electron densities were formed just beneath the apical membranes by microfilaments which surrounded the invaginations. The electron density of each layer was gradually decreased as being apart from the invaginations. The extremities of some bacteria in the invaginations were deformed into sharpened shapes. The cell walls of the extremities of the bacteria were occasionally dissolved in the invaginations, and their cytoplasms were slightly swollen with low electron densities. In some invaginations, the attached bacteria were eliminated to leave their fragments such as filamentous debris and a part of cell walls. Finally these remnants disappeared completely. When the bacterial colonies existed in the middle region of the FAE, the attachment of bacteria resulted in the engulfment of bacteria by M cells. The degenerated bacteria whose cytoplasmic matrices were separated into high electron dense materials and cleared materials were occasionally engulfed by ordinary microvillous columnar epithelial cells or goblet cells throughout the FAE. These findings suggest that the epithelial cells reject the attachment of live indigenous bacteria and that the M cells absorb indigenous bacteria in rat Peyer's patches.

The mechanism of physical elimination of indigenous bacteria was ultrastructurally and immunohistochemically investigated in microvillous columnar epithelial cells of Peyer's patches and intestinal villi of the rat jejunoileum. From ultrastructural observation, the microfilaments accumulated to form several electron-dense layers beneath the bacteria adhering to the cell membrane, which was slightly invaginated in the epithelial cells of Peyer's patches and intestinal villi. As the microfilamentous layers were forming, the end portions of invaginations were deformed into a cone-shape and were finally collapsed. At the same time, the end portions of the adhered bacteria were also deformed into cone-shapes. The bacterial cells were moved back toward the invagination orifices with no morphological change in their inner structure. From immunohistochemical observation, beta-actin and nonmuscle-type myosin were detected at the thin layer just beneath the invaginated cell membrane. These findings suggest that indigenous bacteria which adhere to epithelial cells are removed by only a physical action of actin and myosin filaments, but are not killed. This bacterial cell removal system might lead to the establishment of a settlement of indigenous bacteria on host cells.

The differentiation process of immature microvillous epithelial cells to M cells and the fate of M cells in the follicle-associated epithelium (FAE) of the mucosa-associated lymphoid tissues are still unclear. In this study, the differentiation process and the fate of M cells were clarified in rat Peyer's patches under a transmission electron microscope. Almost all immature epithelial cells were found to possess long, slender microvilli, which gradually shortened, thickened and dispersed as the immature epithelial cells migrated away from the crypt orifices. These morphological changes started in the centers and moved to the peripheries of the apical surfaces of epithelial cells, accompanied by the protrusion of apical cytoplasm out of the terminal web. During these changes, the bundles of microfilaments of microvilli never shortened, and both small vesicles in the apical cytoplasm and tiny invaginations of the apical membranes were found. The intraepithelial migrating cells gradually accumulated to form typical intraepithelial pockets. In all FAE, there was no morphological sign of cell death in M cells. The rearrangement of microfilament bundles, the reconstruction of microvilli and the disappearance of pockets resulted in the transformation of M cells into microvillous epithelial cells. These serial ultrastructural changes suggest that M cells are a temporal and transitional cell type caused by the active engulfment of luminal substances and that when the engulfment ceases, the M cells transform into mature microvillous epithelial cells.

It is well known that some caspases in apoptosis is involved in determinant of terminal differentiation and maturation of various cells. Our previous study ultrastructurally clarified the differentiation into M cells from immature microvillous epithelial cells and the redifferentiation from M cells to microvillous epithelial cells in the follicle-associated epithelium (FAE) of rat Peyer's patch. In this study, the difference of epithelial apoptosis between the FAE of Peyer's patch and intestinal villi was immunohistochemically investigated in rat jejunoileum. As a result, cleaved caspase-3 was limited to several epithelial cells at the tip of FAE, whereas almost all of the epithelial cells were cleaved caspase-3 positive in intestinal villi. Cleaved caspase-9 was detected only in a few exfoliating or exfoliated epithelial cells of both FAE and intestinal villi. Nuclear DNA-fragmentation was detected only in several epithelial cells of the tip of FAE, while it was expressed from the middle regions in the intestinal villi. The DNase I expression of the epithelial cytoplasm was much weaker in FAE than in intestinal villi. Bcl-x expression was restricted in the apical cytoplasms of epithelial cells in the FAE, whereas it was restricted in whole cytoplasms in villous epithelial cells. These findings suggest that the progression of the apoptotic process in the epithelial cells of FAE is later than in the intestinal villi, so that the possibility of epithelial differentiation might be remained in the FAE, unlike in the intestinal villi.

Our previous study clarified that the apical regions of both the follicle-associated epithelium (FAE) of Peyer's patches and the intestinal villi are the only adhesion sites of indigenous bacteria in rat jejuno-ileum. To survey the ligands against bacterial lectins, sugar expression patterns on epithelial cells were lectin-histochemically investigated using 21 lectins in the jejuno-ileal Peyer's patches of rats. As a result, (D-glcNAc)(2-4), detected by Solanum tuberosum (STL) and by Lycopersicon esculentum (LEL), and beta-D-gal(1-3)-D-galNAc detected by Peanut agglutinin (PNA), were strongly expressed on the brush borders of the apical regions of the FAE and the intestinal villi. On the other hand, neither sugar was expressed on the brush borders of the basal regions of both FAE and intestinal villi. The positive intensities for the lectins correlated with the progression of epithelial apoptosis in the FAE and in the intestinal villi. Moreover, the double staining with lectin histochemical method and the in situ nick end-labeling method could simultaneously detect the strong expression of both sugars and nuclear DNA fragmentation in epithelial cells at the late apoptotic stage. Other sugar expression patterns in the intestinal villi were similar with those in the FAE. There were no lectins specific for M cells in the FAE. From these findings, the possible sugars of ligands against some indigenous bacterial lectins, expressing specially on the apoptotic epithelial cells, might be narrowed down in rat jejuno-ileum.