The effect of polymyxin B and some mast-cell constituents on mucosal mast cells in the duodenum of the rat

Shifting the balance: antibiotic effects on host-microbiota mutualism

Antibiotics have been used effectively as a means to treat bacterial infections in humans and animals for over half a century. However, through their use, lasting alterations are being made to a mutualistic relationship that has taken millennia to evolve: the relationship between the host and its microbiota. Host-microbiota interactions are dynamic; therefore, changes in the microbiota as a consequence of antibiotic treatment can result in the dysregulation of host immune homeostasis and an increased susceptibility to disease. A better understanding of both the changes in the microbiota as a result of antibiotic treatment and the consequential changes in host immune homeostasis is imperative, so that these effects can be mitigated.

Neonatal antibiotic treatment alters gastrointestinal tract developmental gene expression and intestinal barrier transcriptome

The postnatal maturation of the gut, partially modulated by bacterial colonization, ends up in the establishment of an efficient barrier to luminal antigens and bacteria. The use of broad-spectrum antibiotics in pediatric practices alters the gut bacterial colonization and, consequently, may impair the maturation of the gut barrier function. To test this hypothesis, suckling Sprague-Dawley rats received a daily intragastric gavage of antibiotic (Clamoxyl; an amoxicillin-based commercial preparation) or saline solution from postnatal day 7 (d7) until d17 or d21. Luminal microbiota composition and global gene expression profile were analyzed on samples from small intestine and colon of each group. The treatment with Clamoxyl resulted in the almost-complete eradication of Lactobacillus in the whole intestine and in a drastic reduction of colonic total aerobic and anaerobic bacteria, in particular Enterobacteriacae and Enterococcus. The global gene expression analysis revealed that Clamoxyl affects the maturation process of 249 and 149 Affymetrix probe sets in the proximal and distal small intestine, respectively, and 163 probe sets in the colon. The expression of genes coding for Paneth cell products (defensins, matrilysin, and phospholipase A2) was significantly downregulated by the Clamoxyl treatment. A significant downregulation of major histocompatibility complex (MHC) class Ib and II genes, involved in antigen presentation, was also observed. Conversely, mast cell proteases expression was upregulated. These results suggest that early treatment with a large-spectrum antibiotic deeply affects the gut barrier function at the suckling-weaning interface, a period during which the gut is challenged by an array of novel food-borne antigens.

Lymphatic mast cell response and effect of compound 48/80 on popliteal lymph node reaction in rats following intracutaneous injection of Staphylococcus aureus

To investigate the significance of mast cells in the popliteal lymph node during the development of an inflammatory response, rats were inoculated with 12 x 10(7) colony-forming units of Staphylococcus aureus in the hind foot pad. Numerical changes in mast cells were then measured in the corresponding popliteal lymph node. Six days after inoculation, despite the enlargement of the responding lymph node, a marked decrease in granulated mast cell number, relative to the contralateral node, was observed in the cortical and medullary compartments. Popliteal lymph nodes from rats treated with compound 48/80 and then inoculated with S. aureus showed a higher cortical and medullary hypertrophic response and a significant increase in degranulated/weakly basophilic mast cell number in the lymph node tissue. The findings suggest that (1) Staphylococcus aureus induces a reduction in granulated mast cell number in the cortical and medullary compartments of regional lymph nodes; (2) pretreatment with compound 48/80 appears to contribute to the lymphoid cell proliferation and the hypertrophic response of lymph nodes induced by S. aureus; and (3) granulated mast cells have a regulatory role on lymphoid cell proliferation.

Repeated antigen challenge in rats induces a mucosal mast cell hyperplasia

BACKGROUND

A link between mast cells and a number of intestinal diseases has been suggested. Treatment of adult rats with connective tissue mast cell degranulating agents has been shown to induce an intestinal mucosal mast cell hyperplasia. We have examined the hypothesis that repeated systemic antigen challenge would similarly up-regulate the mucosal mast cell population.

METHODS

Animals were primed with 10 micrograms of albumin and challenged twice weekly with 3, 30, or 300 micrograms of ovalbumin, subcutaneously, for 4 weeks. The mast cell numbers were assessed histologically. In addition, measurements were made of tissue/mast cell-mediator content.

RESULTS

Repeatedly challenged animals that received 30-micrograms doses of soluble ovalbumin developed a mucosal mast cell hyperplasia in the duodenum 2 weeks after the cessation of treatment. No change in connective tissue mast cell numbers was observed. Repeated administration of 300 micrograms of antigen did not induce a mucosal mast cell hyperplasia. No significant difference between the mucosal mast cell numbers in antigen-challenged and control animals was observed when animals were treated concurrently with the mast cell-stabilizing agent disodium cromoglycate.

CONCLUSIONS

Repeated antigen challenge at doses that induce mast cell activation is associated with an increase in the number of mucosal mast cells.

Eosinophils and mast cell homogeneity of the guinea pig eyelid skin, conjunctiva, and ileum

Mast cell heterogeneity has been described on the basis of differential staining reactions, light microscopic morphology, anatomic location, degranulation after polyamines, biochemical contents, growth requirements, and reactions to lymphokines. We have demonstrated typical "connective-tissue mast cells" by using anatomic criteria, histological staining reactions, electron microscopy, and reaction to compound 48/80 in the guinea pig conjunctiva, eyelid skin, and ileum. A second, much larger population of cells in the ileal mucosa and the conjunctiva, and rarely in the eyelid skin stained reddish-blue with acid toluidine blue in tissue fixed in ethanol-acetate-lead subacetate (BLA) and with alkaline Giemsa in formaldehyde-fixed tissue, did not stain with ethanolic or acid toluidine blue in formaldehyde-fixed tissue or with alkaline Giemsa in BLA-fixed tissue, and did not degranulate after 48/80 treatment. These are features of the rat intestinal "mucosal mast cells"; however, ultrastructural and light microscopic studies with the orcein Giemsa stain demonstrated these cells in the guinea pig to be eosinophils. Tissue culture, biochemical, and immunological studies indicate the existence of a second type of mast cell (bone-marrow-derived mast cell), ultrastructurally almost indistinguishable from the connective tissue mast cell. Our studies demonstrate only one mast cell type in the guinea pig and support the contention that other forms of mast cells are immature forms or variants of the connective-tissue mast cell.

Novel cellular interactions and networks involving the intestinal immune system and its microenvironment

The interactions we have described enable the intestine to respond appropriately to antigenic challenge in an effective and coordinated way. This is of vital importance when one considers the dual role of the intestine as a first line of defence against harmful microorganisms and as the route by which the animal obtains nutrition. Under normal circumstances, these interactions select for an appropriate cell phenotype by providing a network of interactions that contribute to intestinal homeostasis. If there is dysfunction of any component, then other cells will be affected. For example, if down-regulation of the mucosal immune response is not effective, damage to the epithelium, nerves and muscle may occur during an inflammatory response. Similarly, if the integrity of the epithelium is disrupted, damage to the elements of the mucosal immune system may occur. This model would suggest that these interactions must be considered if one wishes to adequately explain diseases such as IBD and design innovative therapeutic regimens. Future interdisciplinary research will shed light on the web of interactions occurring in the intestinal environment and provide a novel view of the respective contributions of the immune system and its local environment to cell differentiation, function and regulation.

Induction of an auto-anti-IgE response in rats. II. Effects on mast cell populations

Immunization of rats with purified rat IgE myeloma (IR2) induces an IgG class autoantibody directed specifically against the IgE isotype. This has variable stimulatory effects on the serum IgE concentration in high IgE-producing BN rats but significantly decreases the serum IgE concentration in the conventional PVG.RT1u strain. We have examined the effects of inducing such an auto-anti-epsilon response on mast cell populations, as defined by their staining characteristics in BN rats. A persistent anti-epsilon response changed the proportions of mast cell types. Those containing highly sulfated, Safranin-positive granules which equate with cells described as connective tissue mast cells (CTMC) were reduced in number in skin, tongue and bone marrow, whereas the less highly sulfated, Alcian Blue-positive mast cells were increased in number in these tissues as well as in the gut, a site rich in the so-called mucosal mast cell. The overall number of mast cells in nonmucosal sites was not significantly changed in anti-IgE-producing rats. The direct effects of anti-epsilon antiserum on mast cells in vivo were investigated using an immediate skin response (ISR) technique. The IgG component of serum from IR2-immunized rats, fractionated by high performance liquid chromatography or eluted from Sepharose 4B-coupled IR2, gave positive ISR in naive rats. The ISR was inhibited by prior incubation of immuno-purified rat anti-IR2 with solid-phase IR2 or with two unrelated IgE myeloma proteins but not with rat IgG. Histological examination confirmed that degranulation of CTMC had occurred at the ISR sites.

Histamine content and histidine decarboxylase activity in the spleen of the magnesium-deficient rat: comparison with the skin and peritoneal mast cells

In young rats, some effects of magnesium (Mg) depletion in the diet on histamine content and histidine decarboxylase (HDC) activity in spleen were studied in comparison with those in the skin and peritoneal mast cells. In the case of the young rats fed a Mg-deficient diet (0.001% Mg), the splenic histamine contents increased to levels about 1.3, 2.8 and 23 times as high as those in the rats fed a control diet (0.07% Mg) on the 4th, 6th and 8th day, respectively; histamine contents in the peritoneal mast cells also increased to about 1.2 and 1.8 times the control levels on the 6th and 8th day, respectively; no change was observed in histamine contents in the skin during 8 days of Mg depletion. HDC activities in the spleen of Mg-deficient rats on the 4th, 6th and 8th day increased to levels about 5.5, 15.5 and 35 times as high as the respective control values; the activities in the skin increased to about 37, 7 and 10 times the control values on the 4th, 6th and 8th day, respectively; while in the peritoneal mast cells, the activities increased to about 1.2 and 2.2 times the control values on the 6th and 8th day, respectively. On the 8th day of the Mg deficiency, some studies were made on the effects of histamine releasers on histamine contents in the spleen and peritoneal mast cells. Compound 48/80 (0.5 microgram/ml) or polymyxin B (5 micrograms/ml) induced a release of histamine from the peritoneal mast cells, but not from the spleen cells isolated from the Mg-deficient rat in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)