development-an-vitro-model-system-for-studying-interaction-equus

Development of an in vitro model system for studying the interaction of Equus caballus IgE with its high-affinity receptor Fc&#949;RI

The interaction of IgE with its high-affinity Fc receptor (Fc&#949;RI) followed by an antigenic challenge is the principal pathway in IgE mediated ...

The University of Sheffield

The binding of immunoglobulin E (IgE) to its high-affinity receptor (FcɛRI) is the central protein interaction in IgE-mediated allergic reactions. The cross-linking of the IgE/FcɛRI complex, through cognate allergens, on the surface of mast cells and basophil cells results in mediator release, and thus leads to the symptoms of type I hypersensitivity responses in mammals. To develop a baseline value for subsequent equine anti-allergy drug and vaccine research, the interaction of equine IgE with its high-affinity FcɛRI receptor was investigated following the cloning and expression of equine IgE with specificity for NIP-HSA (4-hydroxy-5-iodo-3-nitrophenylacetic acid conjugated to human serum albumin). Receptor recognition and effector functions were assessed in Rat Basophil Leukemia (RBL-2H3.1) cells transfected with the α chain of equine and canine FcɛRI. Results obtained showed that the equine FcɛRI receptor recognizes both equine and canine IgE and supports similar β-hexosaminidase release levels from RBL cells transfected with equine FcɛRI, peaking at 36.68% at 100ngml(-1) antigen and 32.00% at 100ngml(-1) antigen respectively. Furthermore, the binding kinetics of the equine IgE to the equine FcɛRI receptor and the canine IgE to the same receptor was measured to be KA=6.33×10(9)M(-1) and KA=1.84×10(9)M(-1) respectively. This research established basic reagents and vitro assay systems to underpin the development of rational therapeutic intervention strategies to combat equine allergic manifestations.

Development of an in vitro model system for studying the interaction of Equus caballus IgE with its high-affinity receptor FcɛRI.

Rituximab, a mouse Fab and human Fc chimeric antibody, has been widely used to treat Non-Hodgkin's lymphoma (NHL). However, only 48% of patients respond to the treatment and complete response rate is below 10%. Also, immunogenicity was reported in 17-20% patients receiving the treatment, making it unsuitable for long term diseases such as autoimmune disorders. It has been a hot research field to "humanize" rituximab toward improved efficacy and reduced immunogenicity.

Characterization of a novel humanized anti-CD20 antibody with potent anti-tumor activity against non-Hodgkin's lymphoma.

The interaction of immunoglobulin E (IgE) antibodies with the high-affinity receptor (FcεRI) is important in anti-parasitic immunity and plays a central role in allergic responses. It has been shown that the human Cε3 domains comprise the binding sites for FcεRIα and crystal structure determination has shown that amino acids in four sites contribute to the high affinity of the interaction. The role of homologous residues within canine IgE-Fc, i.e. amino acids located at Cε2-Cε3 interface (residues 332-337), loop BC (residues 362-365), loop DE (residues 393-396), and loop FG (residues 424-427) in canine Cε3 domain were targeted by site-specific mutagenesis. The functional consequences of the mutations to support (i) IgE-mediated, antigen-induced release of β-hexosaminidase from RBL cells transfected with canine or human FcεRIα and (ii) the affinity of the mutants for the soluble extracellular domain of the α-chain expressed in Pichia pastoris were determined by Surface Plasmon Resonance (SPR). Kinetic analysis supports the observed effects of IgE mutations on stimulus secretion coupling. Potential applications of this study, leading to the generation of an IgE variant with a disabled FcεRIα binding site, are discussed.

Identification of amino acid residues involved in the interaction of canine IgE with canine and human FcεRIα.

The Cε2 and Cε4 domains are considered as scaffolds, allowing Cε3 domains to assume an appropriate orientation to interact with FcεRI (Wurzburg and Jardetzky, 2002; Hunter et al., 2008). Human/canine IgE chimeric antibodies were expressed to assess the nature of the contribution of Cε2 and Cε4 domains to bind to and induce target cell degranulation via FcεRIα. Our results indicate that for (1) Cε3 domains in IgE of canine and human origin are the only necessary region for binding to FcεRIα. (2) The interaction of canine IgE with human sFcεRIα is significantly enhanced by contributions from both Cε2 and Cε4 domains of dog origin. (3) The canine/human IgE chimeric antibody construct rapidly dissociates from its the receptor when the canine Cε2 and Cε4 domains are replaced by the homologous human Fc domains which do not confer a conformation on the Cε3 domain to facilitate stable interaction with canine FcRIα. Kinetic constants for the binding of this chimera to the soluble extracellular domain of the receptor indicate an approximate 120-fold decrease in the affinity for canine sFcεRIα (ka=5.30 × 10(2)M(-1)s(-1)) and a 330-fold increase in the dissociation from canine sFcεRIα (KD=6.9 × 10(-6)M(-1)), compared to the wild type IgE kinetic constants (Ka=6.30 × 10(4)M(-1)s(-1); KD=2.1 × 10(-8)M(-1)). Although canine IgE does engage human FcεRIα, canine Cε2 and Cε4 do not contribute to the high-affinity of interaction with human FcεRIα. Upon replacement of human Cε2 and Cε4 domain by the canine homologues, human IgE Cε3 only retains a low affinity for the human receptor, which shows that Cε2 and Cε4 domains in human IgE Fc contribute significantly to the interaction with its cognate receptor.

Article	Year
Development of an in vitro model system for studying the interaction of Equus caballus IgE with its high-affinity receptor FcɛRI. Veterinary immunology and immunopathology\| PubMed ID: 23485176	2013
Characterization of a novel humanized anti-CD20 antibody with potent anti-tumor activity against non-Hodgkin's lymphoma. Cellular physiology and biochemistry : international journal of experimental cellular physiology, biochemistry, and pharmacology\| PubMed ID: 24022075	2013
Identification of amino acid residues involved in the interaction of canine IgE with canine and human FcεRIα. Molecular immunology\| PubMed ID: 24084098	2014
The role of Cε2, Cε3, and Cε4 domains in human and canine IgE and their contribution to FcεRIα interaction. Molecular immunology\| PubMed ID: 24091297	2014

Hongtu Ye

Biography

JoVE Journal Publications

Other Publications