Hannah J. Gould

IgE in allergy and asthma today

The spreading epidemic of allergies and asthma has heightened interest in IgE, the central player in the allergic response. The activity of IgE is associated with a network of proteins; prominent among these are its two principal receptors, FcεRI (high-affinity Fc receptor for IgE) and CD23, as well as galectin-3 and several co-receptors for CD23, notably CD21 and various integrins. Here, we review recent progress in uncovering the structures of these proteins and their complexes, and in our understanding of how IgE exerts its effects and how its expression is regulated. The information that has emerged suggests new therapeutic directions for combating allergic disease.

THE CRYSTAL STRUCTURE OF IGE FC REVEALS AN ASYMMETRICALLY BENT CONFORMATION

The distinguishing structural feature of immunoglobulin E (IgE), the antibody responsible for allergic hypersensitivity, is the Cε2 domain pair that replaces the hinge region of IgG. The crystal structure of the IgE Fc (constant fragment) at a 2.6-Å resolution has revealed these domains. They display a distinctive, disulfide-linked Ig domain interface and are folded back asymmetrically onto the Cε3 and Cε4 domains, which causes an acute bend in the IgE molecule. The structure implies that a substantial conformational change involving Cε2 must accompany binding to the mast cell receptor FcεRI. This may be the basis of the exceptionally slow dissociation rate of the IgE-FcεRI complex and, thus, of the ability of IgE to cause persistent allergic sensitization of mast cells.

AllergoOncology: the role of IgE-mediated allergy in cancer

Epidemiological studies have suggested inverse associations between allergic diseases and malignancies. As a proof of concept for the capability of immunoglobulin E (IgE) to destruct tumor cells, several experimental strategies have evolved to specifically target this antibody class towards relevant tumor antigens. It could be demonstrated that IgE antibodies specific to overexpressed tumor antigens have been superior to any other immunoglobulin class with respect to antibody‐dependent cellular cytotoxicity (ADCC) and phagocytosis (ADCP) reactions. In an alternative approach, IgE nonspecifically attached to tumor cells proved to be a powerful adjuvant establishing tumor‐specific immune memory. Active Th2 immunity could also be achieved by applying an oral immunization regimen using mimotopes, i.e. epitope mimics of tumor antigens. The induced IgE antibodies could be cross‐linked by live tumor cells leading to tumoricidic mediator release. Thus, IgE antibodies may not only act in natural tumor surveillance, but could possibly also be exploited for tumor control in active and passive immunotherapy settings. Thereby, eosinophils, mast cells and macrophages can be armed with the cytophilic IgE and become potent anti‐tumor effectors, able to trace viable tumor cells in the tissues. It is strongly suggested that the evolving new field AllergoOncology will give new insights into the role of IgE‐mediated allergy in malignancies, possibly opening new avenues for tumor therapy.

Local Somatic Hypermutation and Class Switch Recombination in the Nasal Mucosa of Allergic Rhinitis Patients

Immunoglobulin E is produced by nasal B cells in response to allergen. We have analyzed IgE VH region sequences expressed in the nasal mucosa of patients suffering from allergic rhinitis. VH region sequences were amplified by RT-PCR from IgE+ B cells from nasal biopsies. In two of six patients, sequence analysis clearly demonstrated the presence of closely related IgE+ B cell clones: cells displaying identical signature regions across CDR3/FWR4, indicating a common clonal ancestry, but a mixture of shared and diverse somatic mutations across the VH region. Furthermore, in one of the two patients exhibiting related IgE+ B cell clones, five IgA+ B cell clones, related to the IgE+ B cell family, were also isolated from the patient’s nasal mucosa. This evidence, combined with the local expression of mRNA transcripts encoding activation-induced cytidine deaminase, suggests that local somatic hypermutation, clonal expansion, and class switch recombination occur within the nasal mucosa of allergic rhinitics. The presence of related B cells in the nasal mucosa does not appear to result from the random migration of IgE+ cells from the systemic pool, as analysis of a nonatopic subject with highly elevated serum IgE did not exhibit any detectable VH-Cε transcripts in the nasal mucosa. We have provided evidence that suggests for the first time that the nasal mucosa of allergic rhinitics is an active site for local somatic hypermutation, clonal expansion, and class switch recombination, making it of major significance for the targeting of future therapies.

Enumeration of rabbit reticulocyte ribosomal proteins

Abstract The number of rabbit reticulocyte ribosomal proteins resolved by a new method of two-dimensional polyacrylamide gel electrophoresis closely approaches the total number in the ribosome. Proteins which migrate together in one-dimensional electrophoresis separate into as many as 4 or 5 zones in the two-dimensional system. The use of sodium dodecyl sulphate in the second dimension provides an estimate of the molecular weight of all 63 resolved proteins.

Mucosal tissue polyclonal IgE is functional in response to allergen and SEB

To cite this article: Zhang N, Holtappels G, Gevaert P, Patou J, Dhaliwal B, Gould H, Bachert C. Mucosal tissue polyclonal IgE is functional in response to allergen and SEB. Allergy 2011; 66: 141–148.

Comparison of IgE and IgG antibody-dependent cytotoxicity in vitro and in a SCID mouse xenograft model of ovarian carcinoma.

Allergic reactions are mediated by IgE antibodies bound to high‐affinity receptors on mast cells in peripheral tissues and are characterized by their immediacy and hypersensitivity. These properties could also be advantageous in immunotherapy against cancer growth in peripheral tissues. We have constructed chimeric IgE and IgG1 antibodies with murine V regions and human C regions corresponding to the MOv18 monoclonal antibody against the human ovarian tumor‐associated antigen, folate binding protein. The antibodies exhibited the expected binding affinities for antigen and Fc receptors, and effector activities with human basophils and platelets in vitro. The protective activities of MOv18‐IgE and MOv18‐IgG1 were compared in a SCID mouse xenograft model of ovarian carcinoma. The beneficial effects of MOv18‐IgE were greater and of longer duration than those of MOv18‐IgG1. Our results suggest that the allergic reaction could be harnessed for the suppression of ovarian tumors.

IgG4 inhibits peanut-induced basophil and mast cell activation in peanut-tolerant children sensitized to peanut major allergens.

Background Most children with detectable peanut-specific IgE (P-sIgE) are not allergic to peanut. We addressed 2 non–mutually exclusive hypotheses for the discrepancy between allergy and sensitization: (1) differences in P-sIgE levels between children with peanut allergy (PA) and peanut-sensitized but tolerant (PS) children and (2) the presence of an IgE inhibitor, such as peanut-specific IgG4 (P-sIgG4), in PS patients. Methods Two hundred twenty-eight children (108 patients with PA, 77 PS patients, and 43 nonsensitized nonallergic subjects) were studied. Levels of specific IgE and IgG4 to peanut and its components were determined. IgE-stripped basophils or a mast cell line were used in passive sensitization activation and inhibition assays. Plasma of PS subjects and patients submitted to peanut oral immunotherapy (POIT) were depleted of IgG4 and retested in inhibition assays. Results Basophils and mast cells sensitized with plasma from patients with PA but not PS patients showed dose-dependent activation in response to peanut. Levels of sIgE to peanut and its components could only partially explain differences in clinical reactivity between patients with PA and PS patients. P-sIgG4 levels (P = .023) and P-sIgG4/P-sIgE (P < .001), Ara h 1–sIgG4/Ara h 1–sIgE (P = .050), Ara h 2–sIgG4/Ara h 2–sIgE (P = .004), and Ara h 3–sIgG4/Ara h 3–sIgE (P = .016) ratios were greater in PS children compared with those in children with PA. Peanut-induced activation was inhibited in the presence of plasma from PS children with detectable P-sIgG4 levels and POIT but not from nonsensitized nonallergic children. Depletion of IgG4 from plasma of children with PS (and POIT) sensitized to Ara h 1 to Ara h 3 partially restored peanut-induced mast cell activation (P = .007). Conclusions Differences in sIgE levels and allergen specificity could not justify the clinical phenotype in all children with PA and PS children. Blocking IgG4 antibodies provide an additional explanation for the absence of clinical reactivity in PS patients sensitized to major peanut allergens.

Structure based design and characterization of peptides that inhibit IgE binding to its high-affinity receptor

We have designed synthetic peptide inhibitors of the interaction between IgE and its high affinity receptor, FcεRI. The structure of the second domain of CD2 was used as a modelling template for the second α-chain domain of FcεRI, the C-C′ loop of which has been implicated in the interaction with IgE. An L-amino acid peptide and a retro-enantiomeric D-amino acid peptide were designed to mimic the conformation of the C-C′ region. Both peptides were cyclized by disulphide bond formation between terminal cysteine residues, and show mirror image symmetry by circular dichroism analysis. The C-C′ peptide mimics act as competitive inhibitors of lgE binding. The cyclic L- and retro D-peptides exhibited K Ds of approximately 3 μM and 11 μM, respectively, for IgE. Further, the peptides inhibit IgE-mediated mast cell degranulation, an in vitro model of an allergic response.

Activity of human monocytes in IgE antibody-dependent surveillance and killing of ovarian tumor cells

We have previously shown that a chimeric IgE antibody against the folic acid receptor (MOv18 IgE) inhibits tumor growth in a SCID mouse model of ovarian carcinoma. MOv18 IgE gave greater protection than the corresponding chimeric MOv18 IgG1. We have now confirmed these effects in a nude‐mouse model of ovarian carcinoma and have demonstrated for the first time that human monocytes are active in IgE antibody‐dependent cell‐mediated cytotoxicity. Injection of tumor‐bearing mice with PBMC and MOv18 IgE led to infiltration of monocytes into the tumors and prolonged survival of the mice.Incubation of PBMC or purified monocytes and MOv18 IgE with ovarian tumor cells in vitro resulted in tumor cell killing proportional to the expression of unoccupied FcϵRI on monocytes.We observed phagocytosis of tumor cells by the monocytes in vitro. Our results suggest that tumor‐specific IgE antibodies may be exploited for immunotherapy of cancer.