Maturation of the rat small intestine at weaning: changes in epithelial cell kinetics, bacterial flora, and mucosal immune activity

Phenotype of T cells, their soluble receptor levels, and cytokine profile of human breast milk

Human breast milk has important immunoprotective and immunosuppressive functions for an infant. The purpose of this study was to extend the phenotype of milk cells and to measure soluble T cell receptor levels and cytokines in milk, and to compare these with neonatal and adult blood. Milk T cells had a more equivalent CD4:CD8 ratio than blood; milk CD4 T cells mainly expressed the CD45RO (antigen primed/memory) phenotype; milk CD8 cells had an equivalent CD11b:CD28 suppressor:cytotoxic phenotype; and milk T cells had 2-3-fold higher percentages of activated CD4 IL-2R and CD8 HML-1 or CD8 VLA-1 cells than blood. Soluble IL-2R, CD4 and CD8 concentrations were lower in milk than adult blood, although relatively increased when compared to the lower T cell concentration in milk. Breast milk contained high levels of IFN-gamma but low levels of other measured cytokines compared to blood. These distinct differences of T cells and their soluble products are likely to influence an infant's immune system.

Neuropeptide depletion by capsaicin does not prevent mucosal mast cell activation in the rat at weaning

Substance P release by enteric nerves could be an initiating factor for mucosal mast cell (MMC) activation that is associated with weaning in the rat. Capsaicin, which depletes substance P from enteric nerves, should therefore prevent MMC degranulation. Rat pups received either capsaicin (50 mg/kg) or vehicle control subcutaneous injections at 3 and 6 days of life. Capsaicin-treated and control litters were killed at 16, 18, 20, 22, 24 and 26 days of life. MMC activation was measured by serum levels of rat mast cell protease II (RMCPII). Intestinal development was assessed by microdissection to measure villus area, crypt length and crypt cell production rate. RMCPII levels were similar in capsaicin-treated and control rats and peaked at day 22 of life, and intestinal development was not retarded by capsaicin treatment. We conclude that substance P release is unlikely to be an initiating factor for the MMC activation that is associated with weaning.

Immune activation during infancy in healthy humans

Immune activity during infancy was investigated using blood samples from 30 neonates and 52 healthy infants between 2 and 15 months of age attending for immunization. The purpose of this study was to assess the total immune activity of T cells using soluble interleukin-2 receptor (IL-2R) and interferon-gamma concentrations. These were compared with the proportion of CD4 CD45RO-, IL-2R (CD25)-, and transferrin receptor (CD71)-positive peripheral blood lymphocytes. The median duration of breast-feeding and of introduction of solid feeds was 4.2 and 4.0 months, respectively. Compared to neonates, the mean +/- SE soluble IL-2R concentration peaked at 4 months of age (1670 +/- 94 vs 3060 +/- 252 U/ml; P < 0.0001), as did pooled interferon-gamma levels. The percentage of CD4 CD45RO T cells remained low and the proportion of activated peripheral blood lymphocytes decreased during infancy. We conclude that noncirculatory immune activity is increased during infancy and this is associated with weaning.

Murine intestinal mucins inhibit rotavirus infection

BACKGROUND

Mucin, a population of polymeric glycoproteins, constitutes the primary component of the mucus layer that overlies the gastrointestinal tract. These studies aimed to determine whether murine intestinal mucins inhibit rotavirus infection.

METHODS

Murine intestinal mucins were obtained by scraping segments of mouse intestine and purification via CsCl gradient centrifugation and sepharose 4B chromatography. Inhibition of infection was determined by quantitation of immunoperoxidase-stained cells after infection with mucin-rotavirus mixtures.

RESULTS

Crude and purified intestinal mucins from suckling and adult mice are potent inhibitors of replication of a simian rotavirus, rhesus rotavirus (RRV), but weak inhibitors of other rotaviruses. In all preparations, colonic mucins were more potent inhibitors of RRV than small intestinal mucins. Suckling mucins neutralized RRV more effectively than adult mucins. In a panel of rotavirus reassortants, susceptibility to mucin inhibition correlated with the ability to hemagglutinate human type O erythrocytes and with RRV gene 4. Murine intestinal mucin inhibited RRV binding to MA104 cells, suggesting inhibition of virus-cell attachment to be the mechanism for neutralization. Mercaptoethanol or neuraminidase inhibited mucins' anti-RRV activities, implying the functional importance of mucins' polymeric structure and sialic acid content.

CONCLUSIONS

These findings suggest that intestinal mucins represent a barrier to certain rotavirus infections.

The interactive role of mucosal T lymphocytes in intestinal growth, development and enteropathy

Over the past 15-20 years, research has progressively focused on the mucosal T cell as the central factor in the initiation of physiological or pathological changes, first in the growth and maturation of the early (postnatal) intestine, and second in adult-type enteropathies resulting from sensitivity to either food or pathogen-derived antigens. T cell-mediated events may be measured, for example, in terms of specific immunopathologic patterns of change and injury, such as type 1 (lymphocyte infiltration), type 2 (crypt hyperplasia) and type 3 (flat-destructive), which can be recognized and quantitated microscopically; by determination of lymphocyte reactivity through secretion of interleukin-2 receptors (IL-2R) into plasma or expression by mucosal lymphocytes; by quantitation of lymphocyte subsets emigrating into inflamed tissues by immunoperoxidase-labelled monoclonal antibodies; or by the determination of T cell receptor polymorphisms. Alterations in intestinal growth, structure and function at weaning are likely to be T cell-mediated as they are analogous to the same type 1/2 lesions that reflect modulation of adult mucosal architecture in food and parasite-induced hypersensitivity reactions. Enteropathies associated with HIV infection and T cell deficiency display a milder degree of villous flattening and impaired crypt hyperplasia than that typical of gluten-sensitivity, suggesting a reversion to lesser degrees of mucosal pathology (type 1/2). Clearly more information will accrue; meanwhile the remarks in this brief survey should provide a firm basis whereby clinician and scientist can meet, and together recognize and further dissect the modulatory effect of T lymphocytes on mucosal structure and function.

Immune defense to dietary cow milk in healthy infants

The healthy young infant is immunologically adapted to receiving vast amounts of antigens in diet. At the age of 6 months, nine infants were put on a CM elimination diet for 3 weeks and then challenged with CM. Gut immune response was evaluated indirectly with ELISPOT assay at 6 months, after CM elimination (Day 1) and challenge (Day 8), and at 11 months. CM elimination decreased the numbers of immunoglobulin secreting cells (ISC): in the IgM class from mean [95% CI] 4969 [2555, 9653] at 6 months to 1716 [1024, 2873]/10(6) cells on Day 1 (t = 3.14, p = 0.01); and in the IgG class from 5547 [3562, 8630] to 2684 [1383, 5208]/10(6) cells (t = 3.29, p = 0.01). CM challenge further reduced inter-individual variation, and at 11 months the scatter of ISC was comparable to that at 6 months. Specific antibody-secreting cells of the IgA and IgG class were seen at 6 months and again at 11 months, while specific IgM-secreting cells persisted throughout the dietary manipulation. The results indicate that diet profoundly affects the immune defense system, and further suggest that a focused immune response is vital in acquisition of tolerance to dietary antigens.

Intestinal changes in puppies infected with Toxocara canis

Small intestinal histopathology and absorption were examined in Beagle puppies infected with either a moderate or a low burden of Toxocara canis. Infection with T. canis significantly reduced absorption of xylose, but only slightly delayed absorption of para-aminobenzoic acid. Fat assimilation was reduced and faecal proteolytic activity was increased. A significant reduction in villous height occurred and was inversely related to the extent of the infection. Villous goblet cell numbers, particularly those in the luminal third of the villus, were lowest and crypt goblet cell numbers were highest in the most heavily infected of the puppies. Villous goblet cell numbers increased rapidly after treatment of the puppies with piperazine or after the spontaneous elimination of the T. canis infection while crypt goblet cell numbers were less affected by elimination of the parasites. Intra-epithelial lymphocyte numbers were lowest in 33- to 37-day-old puppies infected with greater than 127 T. canis and highest in 44- to 46-day-old puppies losing their infection. Infection with T. canis had no apparent effect on mast cell numbers or pyroninophilic cell numbers in the lamina propria.

Quantitative histological study of enteropathy associated with HIV infection

A quantitative histological study was performed on small intestinal biopsies from eight ambulatory patients with HIV infection (AIDS/AIDS-related complex, ARC) and compared with those from 16 normal subjects. Enteropathy was assessed by measurement of villus area, crypt length and mitotic count, as well as duodenal counts of intraepithelial lymphocytes, mucosal mast cells and goblet cells. Enteropathy in subjects with AIDS/ARC was shown by reduced mean villus area of 0.363 (SD 0.081) compared with 0.500 (SD 0.064) mm2 in control subjects (p less than 0.0001), while intestinal crypts were of similar length with 239 (SD 36) compared with 225 (SD 28 microns, but mitotic count was increased to 3.8 (SD 1.2) compared with 2.4 (SD 0.8) (p = 0.01) in the same control subjects. These results indicate villous atrophy with impaired crypt hyperplasia. Duodenal cell counts showed similar numbers of mucosal mast cells, intraepithelial lymphocytes and goblet cells in AIDS/ARC patients and fifteen control subjects.

The effect of cyclosporin A in delaying maturation of the small intestine during weaning in the rat

As maturation of the small intestine has similar features to an immunologically mediated reaction, we studied the effect of the immunosuppressive agent, cyclosporin A (CyA), on the development of the small intestine during weaning in the DA x PVG rat. Intestinal development was measured by villus area, crypt length, crypt cell production rate (CCPR), and disaccharidase activity. Rat pups received either cyclosporin A (7.5 mg/kg daily subcutaneously) or polyethoxylated castor oil (Cremophor, drug vehicle) subcutaneously from 12 days of age. Cremophor- and CyA-treated litters were killed at 18, 20, 22, 24, and 26 days of age. CyA-treated animals had retarded weight gain, lower mesenteric lymph node and spleen weights, fewer intraepithelial lymphocytes, and reduced systemic secretion of rat mucosal mast cell protease II. CyA treatment retarded any increase in villus area, crypt length and CCPR until day 26 of age. Lactase activity was retained longer, and sucrase and maltase induction was delayed. We conclude that CyA retarded normal development of the small intestine, but some maturation still occurred at the end of weaning.

Association of maturation of the small intestine at weaning with mucosal mast cell activation in the rat

Maturation of the small intestine at weaning has some features in common with immunological reactions involving the gut mucosa. Mucosal mast cell (MMC) activation is a prominent feature of both IgE and cell-mediated mucosal immune responses. MMC activation was therefore studied during the weaning period by measurement of rat mucosal mast cell protease II (RMCPII) release into the systemic circulation as well as MMC counts and jejunal RMCPII content. Maturation of the small intestine was measured by changes in villus and crypt length, and in crypt cell production rate (CCPR). At 3 weeks of age, serum RMCPII increased 17-fold and MMC showed features of degranulation. At the time of weaning (2-4 weeks), villus and crypt length and CCPR increased progressively to adult values. After weaning, serum RMCPII declined slowly to normal adult levels and MMC regained a normal appearance. This study showed a close association between MMC activation and maturation of the small intestine during the weaning period.