Studies of the IgE binding sites to rat mast cell receptor with proteolytic fragments and with a monoclonal antibody directed against epsilon heavy chain: evidence that the combining sites are located in the C epsilon 3 domain

The nucleotide sequence of dinitrophenyl-specific IgE and Fc(epsilon)RI alpha-subunit obtained from FE-3 hybridoma cells

FE-3 cells were established by Hanashiro et al. by hybridizing mouse myeloma cells (Sp2/0-Ag14/SF) with rat spleen cells that were freshly isolated from Brown-Norway rats sensitized with DNP-As. FE-3 cells can constitutively secrete IgE without stimulation by cytokines. Our preliminary experiments demonstrated that the IgE secretion was decreased at 3 days after start of culture and the addition of exogenous IgE into culture media depressed the secretion of IgE. Thus, we hypothesized that the IgE production in FE-3 cells may be regulated by a signal transduction through the binding of IgE to its high affinity receptor (Fc(epsilon)RI) or to an IgE binding protein on the cell surface. In this study, we aimed to identify the nucleotide sequence of IgE FE-3 and compared with those of mouse IgE and IgE IR162 to find a structural heterogeneity in the Fc region of IgE FE-3. We also tested if the mRNA of Fc(epsilon)RI was expressed in FE-3 cells using the reverse transcriptase-polymerase chain reaction (RT-PCR) method with the combination of sequencing analysis. Consequently, the cDNA sequence of IgE FE-3 was identical to that of the CH3 and CH4 domains in the epsilon-chain of rat IgE IR162, whereas the cDNA of Fc(epsilon)RI was identical to that of mouse, suggesting that the genes of IgE FE-3 and Fc(epsilon)RI was derived from that of rat spleen cells and mouse myeloma cells, respectively.

Kinetics and quantitation of eosinophil and neutrophil recruitment to allergic lung inflammation in a brown Norway rat model

We quantitated neutrophil and eosinophil migration into lung parenchyma using specific peroxidase enzyme assays, and into the bronchoalveolar compartment by bronchoalveolar lavage (BALF), in sensitized brown Norway (BN), Fischer, and Lewis rats and also assessed the lungs by histopathology. Fourteen days after sensitization with ovalbumin (OA in alum [given subcutaneously] and OA with Bordetella pertussis [given intraperitoneally]), rats were challenged with an OA aerosol for 1 h. In BN rats, there was marked perivascular and peribronchial edema, focal hemorrhages, and increase in lung wet weight and BALF protein content, accompanied by neutrophilic infiltration at 3-14 h postchallenge. Few eosinophils were seen at 14 h in lung tissue or in BALF. Neutrophils peaked at 24 h in parenchyma ([94 +/- 7] x 10[6]) and in BALF ([2.7 +/- 0.4] x 10[6]) and declined rapidly thereafter. Marked eosinophil infiltration into parenchyma was apparent by 24 h. Eosinophil accumulation peaked at 48 h in parenchyma ([127 +/- 18] x 10[6]) and at 72 h in BALF ([10 +/- 2.4] x 10[6]), comprising up to 85% of lavage cells at this time. Lung eosinophilia persisted for at least 6 d with only a slow decline or clearance, not approximating baseline until day 13 after challenge. Histopathology showed peribronchial and interstitial eosinophilic pneumonia, most severe on day 3. In contrast to the BN rats, essentially no pulmonary inflammation was observed in Lewis and Fischer rats. This model in the BN rat, and the specific peroxidase assays for quantitating tissue eosinophils and neutrophils, should be useful for investigating the regulation of allergen-induced eosinophil and neutrophil migration into and clearance from the lung.

The nature and importance of the inter-epsilon chain disulfide bonds in human IgE

IgE antibodies are best known for their pathological role in allergy. The class-specific effector sites are located in the epsilon chains; these form covalent dimers via two cystine residues (Cys241 and Cys328) linking opposite C epsilon 2 domains. The nature and biological significance of the inter-epsilon chain disulfide-bond arrangement is unresolved. For structural and functional analysis site-specific mutations were introduced into the C epsilon 2 domain of recombinant human IgE. The introduction of an additional cyanogen bromide cleavage site (His246----Met) facilitated the identification of parallel disulfide bond pairing. This linkage was also confirmed for myeloma IgE PS by sequence determination of disulfide-linked C epsilon 2 dimers. Substitution of Cys241 and Cys328 by Ser does not destroy receptor binding, but reductive alkylation, or the replacement of Cys328 by Met, leads to loss of activity. This shows that covalent dimerization is not essential for IgE/receptor interaction and points to the importance of the structural integrity of the site surrounding Cys328, visualized in a new model of human Fc epsilon.

Proteolytic digestion of mouse IgE

Conditions are described for the preparation of F(ab')2 and Fab fragments of mouse IgE. Papain, pepsin or trypsin each produced F(ab')2 fragments with Mr approximately equal to 130,000 which yielded Fab fragments on further digestion. The release of Fab fragments from F(ab')2 resulted from further cleavage of the H chain. Pepsin, and especially trypsin appear more suitable for the preparation of F(ab')2 because of the difficulty of separating a 93 kDa by-product from the F(ab')2 produced by papain. The best yields of purified Fab were obtained with papain. Rates of digestion were in the order, pepsin approximately equal to trypsin much greater than papain.

Monoclonal antibodies specific for human IgE-producing B cells: a potential therapeutic for IgE-mediated allergic diseases

Monoclonal antibodies (MAbs) specific for surface antigens of lymphocytes are being used to target and deplete tumorous or normal lymphocytes in vivo. Here, we report evidence for the existence of antigenic epitopes on IgE that are accessible on IgE-secreting B cells but not on other cells bearing IgE. Among 42 murine MAbs specific for human IgE, two were shown by fluorescence flow cytometric analyses to bind to IgE-secreting cell lines but not to IgE bound to high-affinity IgE.Fc receptors (Fc epsilon RI) on basophils or low-affinity IgE receptors (Fc epsilon RII) on other cell types. Neither could they induce histamine release from basophils of various donors even under very permissive conditions. These antibodies may be useful for targeting IgE-secreting B cells in patients suffering from IgE-mediated allergies.

Production of large numbers of hybridomas producing monoclonal antibodies against rat IgE using mast cell-deficient w/wv and sl/sld strains of mice

A number of different mouse strains and immunization protocols were used to attempt to make monoclonal antibodies against rat IgE for use in studies of the structure, biological activities and regulation of this class of antibody. Successful production of large numbers of monoclonal antibodies was achieved when mast cell deficient (w/wv and sl/sld) but not conventional (BALB/c, CAF1 or SJL) mice were used. These results suggest that the poor response of conventional strains of mice to rat IgE may be due to the presence of mast cells bearing high affinity receptors for IgE in these mice.