Wheat germ agglutinin stimulates exocytotic histamine secretion from rat mast cells in the absence of extracellular calcium

The dietary intake of wheat and other cereal grains and their role in inflammation

Wheat is one of the most consumed cereal grains worldwide and makes up a substantial part of the human diet. Although government-supported dietary guidelines in Europe and the U.S.A advise individuals to eat adequate amounts of (whole) grain products per day, cereal grains contain “anti-nutrients,” such as wheat gluten and wheat lectin, that in humans can elicit dysfunction and disease. In this review we discuss evidence from in vitro, in vivo and human intervention studies that describe how the consumption of wheat, but also other cereal grains, can contribute to the manifestation of chronic inflammation and autoimmune diseases by increasing intestinal permeability and initiating a pro-inflammatory immune response.

Dietary wheat germ agglutinin modulates ovalbumin-induced immune responses in Brown Norway rats

The trend towards an increased consumption of minimally processed plant food results in a higher intake of non-nutritive compounds such as lectins. Lectins are typically globular proteins that are resistant to digestion in the gastrointestinal tract. They affect the integrity of the intestinal epithelium and the absorption of dietary antigens, and induce the release of allergic mediators from mast cellsin vitro. Based on this information we have studied whether dietary wheat germ agglutinin (WGA) could be involved in triggering food allergies. Brown Norway rats were immunized intraperitoneally using ovalbumin (OVA; 10 μg/rat) and 10 d later treated for five consecutive days with WGA (10 mg/rat per d) administered intragastrically. Rats were then orally challenged with OVA (100 μg/rat) 1 h after the last WGA application, and blood was collected 4 h later. Immunological responses (anti-OVA immunoglobulins E and G, rat mast cell protease II, interferon-γ and lymphocyte proliferation) were measured and lymphocyte subpopulations were determined. In immunized rats WGA treatment resulted in increased serum rat mast cell protease II concentrations (pre-challenge 0.26 (SE 0.08) ΜG/ML, POST-CHALLENGE 0.49 (se 0.09) μg/ml; P<0.01) 4 h after the OVA challenge. After 5 d serum concentrations of anti-OVA immunoglobulin E were significantly increased only in the immunized controls (absorbance at 405 nm on days 14 and 19 was 0.09 (se 0.008) and 0.24 (se 0.046) respectively; P=0.02), while in WGA-treated rats no significant increase was seen (0.08 (se 0.004) and 0.15 (se 0.037 respectively; P=0.14). CD4+: CD8+T lymphocytes in the spleen was significantly increased at this time (OVA 1.1 (sd 0.2), OVA+WGA 1.4 (sd 0.1), P<0.05). The treatment did not impair the proliferation and interferon-γ production of mesenteric lymphocytes. In conclusion, these data suggest that high dietary intake of lectins such as WGA may affect the allergic response towards oral antigens in the gut-associated lymphoid tissue.

Differential effect of plant lectins on mast cells of different origins

Histamine release induced by plant lectins was studied with emphasis on the carbohydrate specificity, external calcium requirement, metal binding sites, and mast cell heterogeneity and on the importance of antibodies bound to the mast cell membrane to the lectin effect. Peritoneal mast cells were obtained by direct lavage of the rat peritoneal cavity and guinea pig intestine and hamster cheek pouch mast cells were obtained by dispersion with collagenase type IA. Histamine release was induced with concanavalin A (Con A), lectins from Canavalia brasiliensis, mannose-specific Cymbosema roseum, Maackia amurensis, Parkia platycephala, Triticum vulgaris (WGA), and demetallized Con A and C. brasiliensis, using 1-300 microg/ml lectin concentrations applied to Wistar rat peritoneal mast cells, peaking on 26.9, 21.0, 29.1, 24.9, 17.2, 10.7, 19.9, and 41.5%, respectively. This effect was inhibited in the absence of extracellular calcium. The lectins were also active on hamster cheek pouch mast cells (except demetallized Con A) and on Rowett nude rat (animal free of immunoglobulins) peritoneal mast cells (except for mannose-specific C. roseum, P. platycephala and WGA). No effect was observed in guinea pig intestine mast cells. Glucose-saturated Con A and C. brasiliensis also released histamine from Wistar rat peritoneal mast cells. These results suggest that histamine release induced by lectins is influenced by the heterogeneity of mast cells and depends on extracellular calcium. The results also suggest that this histamine release might occur by alternative mechanisms, because the usual mechanism of lectins is related to their binding properties to metals from which depend the binding to sugars, which would be their sites to bind to immunoglobulins. In the present study, we show that the histamine release by lectins was also induced by demetallized lectins and by sugar-saturated lectins (which would avoid their binding to other sugars). Additionally, the lectins also released histamine from Rowett nude mast cells that are free of immunoglobulins.

Sugar-specific inhibitory effects of wheat germ agglutinin and phytohemagglutinin-E4 on histamine release induced by basic secretagogues from rat peritoneal mast cells and their possible action sites

The histamine release induced by compound 48/80, bradykinin or polyethylenimine with a molecular weight of 600 (PEI6) was inhibited by wheat germ agglutinin (WGA) and phytohemagglutinin E-subunits (PHA-E4), and the inhibition was specifically reversed by N-acetyl glucosamine and N-acetyl galactosamine, respectively. Concanavalin A (Con A) and phytohemagglutinin L-subunits (PHA-L4) did not inhibit the histamine release induced by compound 48/80, bradykinin or PEI6. The histamine release induced by substance P was also inhibited sugar-specifically by WGA and PHA-E4. The binding sites for compound 48/80, bradykinin, PEI6 and substance P, therefore, seemed to especially overlap each other. These binding sites were found to be glycoproteins having affinities to WGA and PHA-E4, but not to Con A and PHA-L4. The binding of WGA and PHA-E4 to the glycoproteins resulted in inhibition of the interaction between the basic secretagogues including bradykinin and substance P and their binding sites on the mast cells. The bindings of five lectins to mast cell glycoproteins were examined by lectin-blotting. Several glycoproteins, which had specific affinities to WGA and PHA-E4, but not to Con A and PHA-L4 were detected. We assumed that the binding sites for basic secretagogues which are coupled with histamine-releasing mechanisms exist among these glycoproteins. A 41-kDa protein (alpha-subunit of pertussis toxin-sensitive G protein) was not detected by WGA, suggesting that the binding sites for the basic secretagogues were not G proteins.

Viability and recovery from degranulation of isolated rat peritoneal mast cells

Using a culture system that allows prolonged maintenance of purified populations of peritoneal mast cells, we have examined them following stimulation by non-immunologic or immunologic agents. Employing phase-contrast microscopy of living cells and various pharmacological manipulations, we have noted that the recovery process includes a reduction in cell size, the probable sealing of exocytotic cavities, a pronounced displacement of the cell nucleus and a resynthesis of histamine. During recovery, mast cells can entrap molecules from the extracellular fluid and later release these substances by a Ca-dependent mechanism. Our results suggest that microfilaments, calmodulin, Ca, and metabolic energy are necessary for recovery.

Mast cell secretion: differences between immunologic and non-immunologic stimulation

Non-immunologic and immunologic stimulation of mast cells have been compared. Non-immunologic stimulation relys heavily on cellular Ca, is unaffected by neuraminidase treatment, shows a rapid inactivation, and elicits no increase in the incorporation of 3H-methyl groups into the lipid fraction. In contrast, stimulation by immunologic agents relys primarily on extracellular Ca, is inhibited by neuraminidase treatment, shows a comparatively slow rate of inactivation, and causes a significant increase in the incorporation of 3H-methyl groups into the lipid fraction. We found no evidence of cross-inactivation or desensitization between immunologic and non-immunologic agents. However, pretreatment of mast cells with neurotensin desensitized them to subsequent stimulation by compound 48/80. Our results support the hypothesis that immunologic and non-immunologic agents activate exocytotic mast cell secretion via separate mechanisms.

Association of 45calcium with rat mast cells stimulated by 48/80: effects of inactivation, calcium and metabolic inhibition

1. Stimulation by compound 48/80 of mast cells deprived of Ca released histamine when Ca was subsequently added. This secretory response was accompanied by a pronounced increase in the amount of cell-associated (45)Ca.2. The level of cell-associated (45)Ca declined as the interval between stimulation by compound 48/80 and the introduction of (45)Ca increased.3. This decline in the amount of (45)Ca paralleled the decline in histamine secretion that is called inactivation and each curve could be fitted by linear regression to a first-order equation with a half-life of between 1 and 2 min.4. When histamine secretion was held constant, the amount of cell-associated (45)Ca steadily and significantly declined as the interval between stimulation and the addition of (45)Ca increased. This decline in the level of (45)Ca was significantly reduced when fully inactivated cells were used.5. The amount of cell-associated (45)Ca could not be significantly reduced by repeated or prolonged washing with EGTA or LaCl(3).6. The addition of the ionphore, A23187, or compound 48/80, to mast cells loaded with (45)Ca by prior stimulation with 48/80 and bathed in Ca-free media, significantly reduced the level of cell-associated (45)Ca. This effect of 48/80 but not of A23187 was prevented by including either dinitrophenol or (45)Ca in the extracellular solution.7. When [(3)H]N-methyl-methoxy-inulin was included with the (45)Ca or added alone, no significant change in the level of cell-associated [(3)H]inulin was found during the course of inactivation.8. Increasing the Ca concentration increased the amount of cell-associated (45)Ca when Ca was added 10 sec after stimulation by 48/80 but not when Ca was added 10 min after stimulation.9. Incubation of mast cells in media containing deoxyglucose and either antimycin A or dinitrophenol prevented both histamine release and any increase in the level of cell-associated (45)Ca in response to stimulation by 48/80. A similar result was obtained using sensitized mast cells stimulated by antigen. The addition of the ionophore, A23187, to the mast cells prompted a significant increase in the level of cell-associated (45)Ca.10. These results are considered to be support for the hypothesis that the process of inactivation to compound 48/80 results from a time-dependent decay in membrane permeability. It is suggested that those events associated with initiating changes in membrane permeability are effected by metabolic inhibition and calcium.

Histamine release from rat mast cells induced by the lectin from the snail, Cepaea nemoralis L. - a counterpart to the triggering action of polycations?

One of the two lectins, occurring in the albumen gland of the snail, Cepaea nemoralis L., is shown to be a histamine releaser from isolated rat mast cells as well as in vivo. The release reaction is induced in the same dosage range as the agglutination of human red blood cells occurs. Both the reactions are inhibitable by the addition of N-acetyl-neuraminic acid. The releasing activity of the lectin seems to be a counterpart to the triggering action of polycations, because its specificity is directed against this sugar.

Neurotensin stimulates exocytotic histamine secretion from rat mast cells and elevates plasma histamine levels

1. Neurotensin stimulated histamine release and granule extrusion when applied to isolated rat peritoneal mast cells. 2. This secretory response was prevented by the removal of calcium or energy and was not accompanied by the release of lactic dehydrogenase. 3. The secretory response produced by neurotensin was prevented by prior treatment of mast cells with cromoglycate. 4. The intravenous injection of neurotensin into anaesthetized rats produced a rapid and significant increase in the level of blood histamine that was dependent upon the dose of neurotensin. 5. Treatment of rats with compound 48/80, 24 hr before neurotensin, abolished the elevation in blood histamine caused by neurotensin. The intravenous injection of cromoglycate 1-2 min before neurotensin greatly reduced the response to neurotensin. 6. The intradermal injection of neurotensin (0.03-30 p-mole) increased capillary permeability in rats pre-treated intravenously with Evans Blue. This response was abolished by the antihistamine, diphenhydramine. Increasing the dose of neurotensin to 300 p-mole partially overcame this inhibition by diphenhydramine. 7. Our results demonstrate that neurotensin can elicit an exocytotic secretory response from isolated rat peritoneal mast cells and elevate histamine levels in blood. It is suggested that some of neurotensin's physiological effects may be due to stimulation of mast cell secretion.