Inhibition of passive sensitization of human peripheral basophils by synthetic human immunoglobulin E peptide fragments

Synthesis and incorporation into cyclic peptides of tolan amino acids and their hydrogenated congeners: construction of an array of A-B-loop mimetics of the Cε3 domain of human IgE

The disruption of the human immunolobulin E-high affinity receptor I (IgE-FcεRI) protein-protein interaction (PPI) is a validated strategy for the development of anti asthma therapeutics. Here, we describe the synthesis of an array of conformationally constrained cyclic peptides based on an epitope of the A-B loop within the Cε3 domain of IgE. The peptides contain various tolan (i.e., 1,2-biarylethyne) amino acids and their fully and partially hydrogenated congeners as conformational constraints. Modest antagonist activity (IC(50) ∼660 μM) is displayed by the peptide containing a 2,2'-tolan, which is the one predicted by molecular modeling to best mimic the conformation of the native A-B loop epitope in IgE.

Novel IgE peptide-based vaccine prevents the increase of IgE and down-regulates elevated IgE in rodents

BACKGROUND

Immunotherapy with anti-IgE antibodies for treatment of allergy is promising but a short half-life and extremely high cost limit its application.

OBJECTIVE

We sought to develop IgE vaccines that induce longer-lasting auto-antibodies to neutralize self-IgE as an alternative therapy.

METHODS

The vaccine was made by conjugating three synthetic peptides corresponding to human IgE receptor-binding sites to a carrier, hepatitis B surface antigen. To test the immunogenicity of the vaccine, rats were immunized with the vaccine or hepatitis B surface antigen as control. Serum IgG titres to human IgE and the IgE of other species were measured. The inhibition by rat antisera of the binding of human IgE to its receptor was assessed by ELISA, flow cytometry analysis, and passive cutaneous anaphylaxis (PCA), and its ability to recognize receptor-bound IgE was examined. The in vivo effect of the vaccine was evaluated in trichosanthin-sensitized mice and rats. In the preventative study, vaccination started before sensitization commenced, while in the treatment study, vaccination started after sensitization. Sensitized mice and rats receiving injections of the carrier served as controls. Trichosanthin-specific IgE was measured using PCA.

RESULTS

Sera from vaccine-immunized rats contained high titre antibodies that reacted with soluble and plate-bound but not with receptor-bound human IgE; they also reacted with mouse, rat, and dog IgE. Furthermore, the sera inhibited the binding of human IgE to its receptor in a dose-dependent manner. In preventative and treatment studies, serum trichosanthin-specific IgE levels were significantly reduced in vaccinated groups compared with controls.

CONCLUSION

Antibodies against self-IgE can be induced by IgE peptide-based vaccines, which are effective in preventing the increase of IgE and in down-regulating IgE in sensitized animals.

Current progress in the understanding of IgE-FcepsilonRI interaction

The last decade has seen a wealth of studies aimed at the characterization of the binding between IgE and its high-affinity receptor, FcepsilonRI. IgE-FcepsilonRI complex formation is a major molecular event in atopic allergy. IgE-FcepsilonRI binding connects allergen recognition to cellular triggering, ultimately leading to disease manifestations. Consequently, pharmacological intervention at this site is of universal relevance for atopic allergy. Until recent years, the complexity of IgE-FcepsilonRI binding, together with the difficulty in obtaining fully functional recombinant IgE and FcepsilonRI derivatives, often led to confusion and difficulty in data interpretation. Major advances in the understanding of this intricate protein-protein interaction have now been accomplished. Most of the current knowledge on the IgE-FcepsilonRI recognition mode derives from long-lasting efforts in the field of structural biology. Protein engineering, high-throughput screening, immunological and biochemical studies also made relevant contributions in this domain. The data accumulated to date predict that IgE and FcepsilonRI use their modular architecture to approach each other in an asymmetric stepwise manner determining a 1:1 stoichiometry. This recognition appears to be enhanced by conformational changes occurring upon binding, leading to the well-known high-affinity. In conclusion, the vast amount of high-quality data available broadened our knowledge on the IgE-FcepsilonRI system; however, the fine structural details of the recognition process are still largely hypothetical. More studies are necessary to provide the experimental comprehensive picture required to carefully design efficient drugs acting at the IgE-FcepsilonRI interface.

Sequence of the dog immunoglobulin alpha and epsilon constant region genes

The immunoglobulin alpha (IGHAC) and epsilon (IGHEC) germline constant region genes were isolated from a dog liver genomic DNA library. Sequence analysis indicates that the dog IGHEC gene is encoded by four exons spread out over 1.7 kilobases (kb). The IGHAC sequence encompasses 1.5 kb and includes all three constant region coding exons. The complete exon/intron sequence of these genes is described.