The receptor with high affinity for IgE on rat mast cells is a functional receptor for rat IgG2a

In vitro modelling of rat mucosal mast cell function in Trichinella spiralis infection

Intestinal infection with the parasitic nematode, Trichinella spiralis, provides a robust context for the study of mucosal mast cell function. In rats, mucosal mast cells are exposed to parasites during the earliest stage of infection, affording an opportunity for mast cells to contribute to an innate response to infection. During secondary infection, degranulation of rat mucosal mast cells coincides with expulsion of challenge larvae from the intestine. The goal of this study was to evaluate the rat bone marrow-derived mast cells (BMMC) and the rat basophilic leukaemia cell line (RBL-2H3) as models for mucosal mast cells, using parasite glycoproteins and antibody reagents that have been tested extensively in rats in vivo. We found that BMMC displayed a more robust mucosal phenotype. Although T. spiralis glycoproteins bound to mast cell surfaces in the absence of antibodies, they did not stimulate degranulation, nor did they inhibit degranulation triggered by immune complexes. Parasite glycoproteins complexed with specific monoclonal IgGs provoked release of rat mast cell protease II (RMCPII) and β-hexosaminidase from both cell types in a manner that replicated results observed previously in passively immunized rats. Our results document that RBL-2H3 cells and BMMC model rat mucosal mast cells in the contexts of innate and adaptive responses to T. spiralis.

IgG2 dominancy and carbohydrate recognition specificity of C3H/He mouse antibodies directed to cross-reactive carbohydrate determinants (CCDs) bearing beta-(1,2)-xylose and alpha-(1,3)-fucose

Few common carbohydrate epitopes consisting of terminal beta-(1,2)-xylose and/or alpha-(1,3)-fucose residues are shared by a variety of glycoproteins from plants, insects and parasitic worms, termed cross-reactive carbohydrate determinant (CCD), and frequently recognized by IgE antibodies of patients with food and/or respiratory allergy, though clinical relevancy of such CCD-specific IgE is still controversial. Attention has also been focused on CCDs from the undesired post-translational modification of recombinant therapeutic proteins produced by transgenic plants and insects. In the present study, to clarify immunogenic potentials of CCD-bearing glycoproteins, the antibody response to a model plant glycoprotein, horseradish peroxidase (HRP) was investigated in a mouse model. C3H/He mice were immunized with HRP plus Al(OH)(3) or Freund's adjuvant, and IgG and IgE responses to CCDs in addition to HRP were analyzed by ELISA using some distinct glycoproteins with known N-glycan structures. IgE response to HRP was induced remarkably, whereas that to CCD was weaker and delayed. Moreover, apparent ratio of the CCD-specific antibodies to HRP-specific ones tended to be higher in IgG2a and IgG2b isotypes than IgG1, IgG3 and IgE. In contrast to rabbit antibodies, the CCD-specific antibodies from the mice gave poor reactivity with bromelain and honeybee phospholipase A2, suggesting the critical role of both beta-(1,2)-xylose and alpha-(1,3)-mannose in the CCD-recognition by the mouse antibodies. Moreover, the mouse antibodies showed weaker cross-reactivity to pollen- and insect-derived glycoproteins than the rabbit ones. Thus, in this mouse model, not only IgE but also IgG2 antibody responses to CCDs were induced by immunizing with a CCD-bearing glycoprotein, suggesting that CCDs affected not only Th2-type but also Th1-type antibody response at least in C3H/He mice.

Expulsion of secondary Trichinella spiralis infection in rats occurs independently of mucosal mast cell release of mast cell protease II

Our aim was to elucidate the contribution of mucosal mast cells to the effector phase of a secondary immune response to Trichinella spiralis. During secondary infection, rats expel 90-99% of T. spiralis first-stage larvae from the intestine in a matter of hours. This phenomenon appears to be unique to rats and has been called rapid expulsion. Primary intestinal infection by T. spiralis induces mastocytosis, and mast cell degranulation occurs when challenged rats exhibit rapid expulsion. These observations have engendered the view that mast cells mediate rapid expulsion. In this study, we report that immunization of adult Albino Oxford rats by an infection limited to the muscle phase did not induce intestinal mastocytosis, yet such rats exhibited rapid expulsion when challenged orally. Although mastocytosis was absent, the protease unique to mucosal mast cells, rat mast cell protease II (RMCPII), was detected in sera at the time of expulsion. We further evaluated mast cell activity in neonatal rats that display rapid expulsion. Pups born to infected dams displayed rapid expulsion, and RMCPII was detected in their sera. By feeding pups parasite-specific mAbs or polyclonal Abs before challenge infection, it was possible to dissociate mast cell degranulation from parasite expulsion. These results indicate that rapid expulsion can occur in the absence of either intestinal mastocytosis or RMCPII release. Furthermore, release of RMCPII is not sufficient to cause expulsion. The data argue against a role for mast cells in the mechanism underlying the effector phase of protective immunity against T. spiralis in rats.

Digested Ara h 1 has sensitizing capacity in Brown Norway rats

BACKGROUND

Food allergies are a public health issue of growing concern, with peanuts in particular being associated with severe reactions. The peanut allergen, Ara h 1, belongs to the cupin plant food allergen family, which, unlike other structural families, appears to be broken down rapidly following gastrointestinal digestion.

OBJECTIVE

Using Ara h 1 as a model allergen, the ability of digested protein to sensitize has been investigated.

METHODS

Ara h 1 was purified from whole roasted peanuts. Intact Ara h 1 was digested in an in vitro model, simulating the human gastrointestinal digestion process. Digestion products were analysed for peptide sizes and their ability to aggregate. Brown Norway (BN) rats, used as an animal model, were immunized with purified intact Ara h 1 or the gastrointestinal digestion products thereof. The sensitizing capacity was evaluated by analyses of specific antibody (IgG1, IgG2a and IgE) responses and ability to trigger mediator release of rat basophilic leukaemia (RBL)-2H3 cells.

RESULTS

The present study showed that Ara h 1 was broken down, resulting in peptide fragments of sizes<2.0 kDa, of which approximately 50% was in aggregated complexes of Mr up to 20 kDa. Ara h 1 digesta were shown to have sensitizing capacity in BN rats, being capable of inducing specific IgG and IgE antibodies. The IgE response was functional, having the capacity to induce specific degranulation of RBL cells.

CONCLUSION

From this study, it can be concluded that lability of a food allergen to gastrointestinal digestion does not necessarily abrogate its allergenic sensitizing potential.

In situ measurement of degranulation as a biosensor based on RBL-2H3 mast cells

A direct degranulation assay has been developed to enable the use of RBL mast cells as a biosensor for screening chemical libraries for drug discovery and environmental toxicity evaluation. Release of beta-hexosaminidase into the extracellular milleu is widely used to characterize cellular components and mechanisms involved in stimulated exocytosis, including those initiated by crosslinking of IgE receptors on mast cells. To adapt this versatile assay for high throughput screening, we developed a direct, in situ method in which beta-hexosaminidase detection is carried out in a single step, convenient for multi-sample processing and thus for biosensor applications. This direct assay is efficient for measuring exocytosis in antigen-stimulated RBL mast cells, detecting antigen concentrations as low as 1 pM. We also demonstrate its utility in detecting inhibition of degranulation by a known pharmacologic inhibitor that blocks Syk tyrosine kinase activity critical for cell activation.

IgG-dependent activation of human mast cells following up-regulation of FcgammaRI by IFN-gamma

It has been reported that FcgammaRI is up-regulated on human mast cells (huMC) by IFN-gamma and aggregation of this receptor using mouse F(ab')(2) specific for receptor-bound, mouse anti-CD64 F(ab')(2) results in activation. To determine whether huMC can similarly be stimulated by aggregation of FcgammaRI-bound human IgG, IFN-gamma-treated, CD34(+)-derived, cultured huMC were sensitized with human immunoglobulins and activation was evaluated following addition of antibodies specific for each IgG isotype. Degranulation was also examined following simultaneous IgG- and IgE-dependent aggregation of FcgammaRI and Fc(epsilon)RI. Activation of IFN-gamma-treated huMC sensitized with 100 ng/ml IgG(1) resulted in 40% beta-hexosaminidase (beta-hex) release; minimal degranulation was observed using IgG(2), IgG(3) or IgG(4). IgG(1)-dependent activation led to PGD(2) and LTC(4) generation as well as elevated cytokine production, most notably TNF-alpha. Preincubation of cells with F(ab')(2) from CD64-specific clones 10.1 and 32.2 reduced IgG(1)-mediated beta-hex release by 46% and 74%, respectively. While IgG-dependent cell stimulation induced half-maximal degranulation by 11 min, IgE-dependent activation resulted in half maximal responses within 1 min. Simultaneous activation of huMC via FcgammaRI and Fc(epsilon)RI led to additive degranulation using suboptimal concentrations of IgG(1) and IgE. Activation of huMC thus may occur via monomeric IgG and FcgammaRI thereby providing a novel paradigm for huMC recruitment into inflammation.

Hypersensitivity disorders in horses

Hypersensitivity is an exaggerated immunologic response to a foreign agent that results in inflammation and organ dysfunction. Hypersensitivity disorders are broadly divided into antibody-mediated and T-cell-mediated reactions. The inflammatory pathways that result in disease are initiated in an antigen-specific manner through Fab portions of antibodies or the T-cell receptor, causing the up-regulation of effector mechanisms designed to clear the offending agent. Effector mechanisms include the generation of inflammatory chemicals such as cytokines and chemokines and the attraction of leukocytes and potentiation of their function. This article reviews current concepts in the immunopathogenesis of hypersensitivity disorders and demonstrates these mechanisms as they apply to equine disease.

Humoral and cellular immune responses in different rat strains on oral exposure to ovalbumin

No adequate enteral sensitization models are available to study food allergy and allergenicity of food proteins. Using a previously described oral sensitization protocol to sensitize Brown Norway rats (BN) to food proteins, the influence of genetically-based strain-specific characteristics of the immune system on the outcome of oral sensitization studies was investigated. BN, Hooded Lister (HL), Piebald Virol Glaxo (PVG) and Wistar rats were daily administered 1 mg of ovalbumin (OVA) by gavage dosing for 42 days without the use of an adjuvants. The highest OVA-specific IgG responses were detected in the BN rats followed by Wistar, HL and PVG rats. OVA-specific IgE responses were only detectable in the BN rats. The cellular immune response was examined by determination of delayed-type hypersensitivity (DTH) reactions in the animals. The response was most pronounced in the HL and Wistar rats. PVG and BN rats showed comparable DTH responses but the responses were significantly weaker than those observed in HL and Wistar rats. It was concluded that the genetic make-up of different rat strains influences the outcome of oral sensitization studies. In addition, using the described oral sensitization protocol, the BN rat seems to be the most suitable strain for inducing oral sensitization.

The effectiveness of different rat IgG subclasses as IgE-blocking antibodies in the rat basophil leukaemia cell model

The degranulation of mast cells in an allergic response is initiated by the aggregation of high-affinity IgE receptors (Fc epsilon RI) by IgE and antigen. Recently it has been shown that such degranulation can be inhibited by cross-linking Fc epsilon RI and low-affinity IgG receptors (Fc gamma RII) which are also expressed by mast cells. The ability of various monoclonal antibodies to block the degranulation of rat basophil leukaemia (RBL) cells sensitized with IgE antidinitrophenyl (DNP) antibodies has been investigated. Sensitized cells were challenged with immune complexes formed using varying concentrations of antigen, and of both high- and low-valency antigen. It is reported here that rat IgG1 antibodies, which are associated in the rat with a Th1-type response, act as highly effective blocking antibodies over a wide concentration range. Rat IgG2a antibodies, which are associated with a Th2-type response, were able only to inhibit degranulation when immune complexes were formed with very low concentrations of high-valency antigen (DNP32-HSA). Under these conditions, some inhibitory activity was seen with high-affinity murine IgA anti-DNP but not with low-affinity rat IgG2b anti-DNP antibody-containing immune complexes. In addition to this inhibitory activity, IgG2a antibodies were shown to be capable of inducing degranulation of cells via unoccupied Fc epsilon RI. These results demonstrate that blocking activity may arise via both inhibitory receptors and by masking of antigen.

The secretion-coupled endocytosis correlates with membrane tension changes in RBL 2H3 cells

Stimulated secretion in endocrine cells and neuronal synapses causes a rise in endocytosis rates to recover the added membrane. The endocytic process involves the mechanical deformation of the membrane to produce an invagination. Studies of osmotic swelling effects on endocytosis indicate that the increased surface tension is tightly correlated to a significant decrease of endocytosis. When rat basophilic leukemia (RBL) cells are stimulated to secrete, there is a dramatic drop in the membrane tension and only small changes in membrane bending stiffness. Neither the shape change that normally accompanies secretion nor the binding of ligand without secretion causes a drop in tension. Further, tension decreases within 6 s, preceding shape change and measurable changes in endocytosis. After secretion stops, tension recovers. On the basis of these results we suggest that the physical parameter of membrane tension is a major regulator of endocytic rate in RBL cells. Low tensions would stimulate endocytosis and high tensions would stall the endocytic machinery.

Characterization of Fc gamma receptors on rat mucosal mast cells using a mutant Fc epsilon RI-deficient rat basophilic leukemia line

A novel rat basophilic leukemia (RBL) 2H3 subline of rat mucosal mast cells deficient in the expression of the gamma chain (RBL-gamma-) has permitted functional characterization of their low-affinity Fc gamma receptors (Fc gamma R). A rat Fc gamma RII analog of the mouse b2 isoform has been earlier identified and its transcript detected in RBL-2H3 cells. We have noew isolated and sequenced the rat Fc gamma RIIb1 isoform and observed differences between its expression in RBL-2H3 and RBL-gamma-. Furthermore, we demonstrate that rat mucosal mast cells express a second, low-affinity Fc gamma receptor, namely the Fc gamma RIII. Stimulation of either cell line with IgG complexes decreased the expression of transcripts for all Fc gamma R. Hence, ligation of Fc gamma R on rat mucosal mast cells apparently regulate their transcription. Selective stimulation through the Fc gamma RII or Fc gamma RII/III systems, respectively, was accomplished by either using RBL-gamma- line or by saturating the Fc epsilon RI on RBL-2H3 with monomeric IgE. RBL-gamma-cells, which do carry Fc gamma RII (but lack Fc epsilon RI and Fc gamma RIII), do not respond to IgG (and IgE) immune complexes as monitored by specific protein tyrosine phosphorylation, degranulation or cytokine secretion. This finding, together with the restoration of the functional phenotype of parental cells upon gamma chain cDNA transfection into RBL-gamma- cells, unequivocally excludes the possible stimulation of rat mucosal mast cells by clustering of their Fc gamma RII. Fc epsilon RI saturation by IgE on parental RBL-2H3 cells completely blocks their response to IgG immune complexes. Thus the Fc gamma R on these cells do not trigger degranulation and this is not due to the absence of Fc gamma RIII as previously suggested. Therefore, co-clustering of Fc gamma RII and Fc gamma RIII on rat mucosal mast cells does not seem to stimulate them. A possible inhibitory role of Fc gamma RII in this process is suggested and discussed.