Impaired autoreactive T cell-induced T cell-T cell interaction in aged mice

Self-Ia-reactive (autoreactive) L3T4+ T cell clones have been shown earlier to stimulate the proliferation of syngeneic naive L3T4+ T cells and initiate a T cell-T cell (T-T) interaction leading to the generation of immunoregulatory circuits. Since aging has been shown to be associated with a decline of the immune responsiveness, age-related alterations in the T-T interaction was investigated in the present study. Using several I-Ed-specific autoreactive T cell clones isolated from 2- to 3-month-old (young) DBA/2 mice as stimulators, it was observed that L3T4+ T cells from 22- to 24-month-old (aged) DBA/2 mice, failed to demonstrate a significant response to the autoreactive T cells. In contrast, L3T4+ T cells from young mice responded strongly to the autoreactive T cell clones. The deficient T-T cell interaction in aged mice correlated with an impaired syngeneic mixed lymphocyte reaction in these mice, thereby suggesting that aging induces a defect both in the autoreactive T cells and in T cells which react with the autoreactive T cells. When exogenous recombinant interleukin 2 (rIL-2), recombinant interleukin 4 (rIL-4), or a combination of these was added to the interaction, it was observed that rIL-4 but not rIL-2 enhanced the T-T interaction in young mice. However, rIL-4 or a combination of rIL-2 and rIL-4 failed to correct the defective T-T interaction in aged mice. Since the T cell network is believed to play an important role in the maintenance of normal immune system homeostasis, the present study suggests that age-related alterations in T and B cell functions and increased susceptibility to autoimmune diseases with age may result from a defect in the T cell network regulation.     

Freeze-etch appearance of the tight junctions in the epithelium of small and large intestine of mice

Summary The ultrastructure of the central layer and the contributing plasma membranes of tight junctions has been studied in epithelia of the jejunum and colon of mice.Examination of freeze-etched plasma membranes of epithelial cells has revealed that they consist of a central layer, with fracturing characteristics similar to bimolecular lipid leaflets, which is covered on both sides with a layer of particles.The fusion of the outer membrane surfaces of adjacent cells in the region of the tight junction leads to the formation of a new common structure consisting of a meshwork of fibrils embedded in a matrix substance. The fibrils probably contain protein. They have a diameter of 65 ± 10 Å and are linked together so that they form around the distal end of each cell a continuous belt-like meshwork which is extended proximally at the joints where three cells meet. As the fibrillar mesh appears to be strongly attached to the central lipid layer of the two adjoining membranes, in contrast to the weakly bound surrounding matrix, it is believed that the fibrils forming the continuous meshwork could be the mechanical coupling and the sealing elements of the tight junction. Their arrangement in the form of a concertinalike mesh would make the whole structure very flexible. In the region of the junction the membranes are constricted along the lines of attachment to the fibrils and bulge outwards,i.e. towards the cytoplasm, in the areas of the matrix material. In the resulting grooves on the cytoplasmic side of the plasma membranes regularly spaced particles with a diameter of 90 ± 10 Å can be detected. Various observations suggest that these particles could be connected through the central layer of the membranes to the fibrils on the other side. This would offer a possible explanation for the known abhesion properties of tight junctions. The described structures are also evaluated in terms of current theories of cell communication.     

Striking phenotypic and functional differences in lamina propria lymphocytes from the large and small intestine of mice

Although intraepithelial T lymphocytes of the large intestine (LI) are known to differ from those of the small intestine (SI) in phenotype and function, differences in LI and SI lamina propria (LP) lymphocyte populations have not been clearly established. In this work we found striking phenotypic differences between SI and LI LP lymphocyte populations from Balb/c mice analyzed by flow cytometry. In the LI most lymphocytes were B cells and the predominant T cells were TCR-alpha beta+, CD8+. In contrast, in the SI most T lymphocytes were CD4+ expressing TCR-alpha beta+, although a higher proportion expressed TCR-gamma delta+ than in the LI. In T cells the expression of adhesion molecules and cytokines was also different between SI and LI. The proportion of LP T cells expressing alpha4beta7 and L-selectin was higher in the LI than in the SI; whereas a greater proportion of cells expressing alpha(E)beta7 were detected in the SI than in LI. Higher proportions of T cells expressing L-selectin and alpha4beta1 were detected in the intraepithelial compartment of the LI than that of the SI, whereas the number of T cells expressing alpha(E)beta7 was much higher in the SI than in the LI. The proportion of T cells spontaneously producing IL-2, IFN gamma, and IL-4 at the intraepithelial and lamina propria, in the small and large intestine, was different indicating that distinctive functional features exist in the lymphocyte populations residing at the different intestinal compartments.     

Gap junctions of the muscles of the small and large intestine

Summary The distribution of gap junctions (nexuses) in various parts of the small and large intestines of the guinea-pig was studied using the freeze-fracture technique and in thin sections. The percentage area of smooth muscle cell surface occupied by gap junctions varies from 0.50% in the circular muscle of the duodenum to zero in the longitudinal muscle of the ileum. In the circular muscle of the jejunum and ileum the area occupied by nexuses is 0.22% (or about 11 m² per cell). The sizes of junctions range from less than 0.01 m² to 0.20 m², with two-thirds of them being smaller than 0.05 m². In the colon, gap junctions are rare, very small and confined to the circular muscle layer. Even the smallest aggregates of intramembrane particles correspond to areas of close apposition between the membranes of adjacent cells; it is therefore justified to interpret them as being gap junctions. Some gap junctions are formed between a smooth muscle cell and an interstitial cell. Gap junctions are not found in the longitudinal muscle of the small intestine; this is in sharp contrast to the abundance of gap junctions in the adjacent circular layer.In the small intestine of cats and rabbits, gap junctions are abundant in the circular muscle layer, whereas they are very small in size and very few in number in the longitudinal muscle layer.The authors wish to thank Mr Peter Trigg and Miss Eva Franke for help and support. This work was supported by grants from the Medical Research Council and the Central Research Fund of the University of London     

Proliferative kinetics of large and small intraepithelial lymphocytes in the small intestine of the mouse.

The proliferative kinetics of the intraepithelial lymphocytes (IL) of the mouse intestine have been evaluated. By inducing mitotic arrest it was found that large IL - constituting about 50% of the IL - showed a mitotic rate of 2.3. Autoradiographic results obtained after two different schedules of 3H-thymidine injections showed that 30% of the large IL were in DNA synthesis, and that the large IL were renewed at a rate comparable to that of blast cells from Peyer's patches, mesenteric lymph nodes and thoracic duct lymph. The small IL were renewed very rapidly compared to small lymphocytes of peripheral lymphoid tissues, although small lymphocytes with lifespans of several weeks were also present in the epithelial sheet. By the use of intestinal perfusion, in vivo, it was estimated that the loss of lymphocytes from intestinal villi into the lumen of the gut was negligible, and it is concluded that the most probable kinetic model for the majority of IL is: B and T lymphoblasts invade the epithelium and undergo mitosis. B lymphoblasts give rise predominantly to plasma cells, and T lymphoblasts give rise to small lymphocytes - probably long-lived - which reenter the circulation.     

Anaerobic bacteria from the large intestine of mice.

Anaerobic bacteria from the colon of laboratory mice were enumerated and isolated using strict anaerobic techniques. Direct microscopic counts revealed 4.4 X 10(10) organisms in each gram (wet weight) of colon contents. Actual cultural counts averaged 3.2 X 10(10) organisms, which was 73% of the direct microscopic count. The tentatively identified genera were Bacteroides, Eubacterium, Fusobacterium, Lactobacillus, Peptostreptococcus, and Propionibacterium. Strains of Fusobacterium, Lactobacillus, Peptostreptococcus, and Propionibacterium were biochemically homogeneous. Strains of Bacteroides and Eubacterium, on the other hand, were biochemically heterogeneous and were subdivided into several distinct groups. The data indicate that many of the isolates are different from previously described species of the respective genera and may belong to new species.     

c-kit immunoreactive interstitial cells of Cajal in the human small and large intestine

 c-kit immunohistochemistry was performed on unfixed frozen sections of human small (duodenum, jejunum, and ileum) and large intestine (ascending, transverse, descending, and sigmoid colon). The c-kit immunoreactive cells in the muscularis externa of the intestinal wall were identified as interstitial cells of Cajal (ICC) and mast cells. ICC were identified by their morphology, localization, and organization based on previous light and electron microscopic studies. In the small intestine, ICC were located primarily in relation to the myenteric plexus of Auerbach, but also in septa between circular muscle lamellae. In the large intestine, ICC were seen in relation to Auerbach’s plexus, but also and in great numbers in the circular muscle layer and in teniae of the longitudinal muscle layer. The morphology of the ICC was similar in the small and large intestine, but the pattern of distribution was obviously different. c-kit immunoreactive mast cells were found predominantly in the inner part of the circular muscle layer. The anti-c-kit method is found to be an easy and reliable method to study at least most of the interstitial cells of Cajal and thereby contribute to further normal and pathological studies. Accepted: 31 July 1997     

Nafenopin-induced proliferation of peroxisomes in the small intestine of mice.

The effect of nafenopin on the epithelial cells of the small intestine of mice was studied. After 17 days the control and nafenopin-treated groups were sacrificed. The tissues were incubated in alkaline DAB medium. Ultra-thin sections of small intestinal tissue from both groups were examined by electron microscopy. Electron micrographs were prepared and examined stereologically so that any morphologic differences in the epithelial cell peroxisomes and mitochondria between the experimental and control groups could be evaluated quantitatively. In the nafenopin-treated group proliferation of peroxisomes occurred, as indicated by significant increases in volume, and surface and numerical density of these structures compared with controls. No such alterations were found in the mitochondria. Our results show that the response of small intestinal epithelial cells to nafenopin is analogous to that produced in hepatocytes by the same drug. Hepatocyte peroxisomes are supposed to be involved in lipid metabolism and it seems that small intestinal epithelial peroxisomes play a similar role.     

Expression and motor effects of secretin in small and large intestine of the rat

Immunocytochemistry and in situ hybridization revealed abundant secretin expressing cells on duodenal villi with a gradual decrease throughout the small intestines of the rat. They were absent in pancreas, stomach and colon. Secretin caused relaxation of rat intestinal longitudinal muscle in vitro. Studies on colon revealed that the secretin-evoked response was unaffected by apamin, tetrodotoxin, L-NAME, VIP or PACAP pretreatment; secretin itself caused desensitization. Addition of VIP or PACAP when the secretin-evoked relaxation was maximal evoked a further relaxation suggesting the presence of distinct receptors. Secretin causes relaxation via activation of secretin receptors located on the smooth muscle and not via any of the related VIP/PACAP receptors.