Antibody Isotypes: IgE

Immunoglobulin E makes up the lowest serum concentration of all isotypes, but it is strongly potent, being associated with mediating hypersensitivity and allergic reactions, in addition to having roles in antiparasitic activity, autoimmune processes, and venom protection.

Since IgE is a monomer composed of two epsilon-heavy chains and light chains, it can only bind two antigens, but the structure of their heavy chain C-terminal regions is crucial for the binding to high-affinity cellular receptor Fc-epsilon R1 and low-affinity CD23.¹

FcɛRI is expressed on mast cells, basophils, Langerhans cells, and eosinophils, with circulating IgE upregulating FcɛR expression on these cells. This expression and upregulation are what allows the highly potent IgE to be responsible for immediate hypersensitivity reactions, parasitic immunity, enhanced cytokine production, and antigen presentation. This ultimately results in cellular degranulation and the release of vasoactive and pro-inflammatory mediators.^2,3

On the other hand, CD23 is mainly expressed on B-cells, T-cells, and antigen-presenting cells, and manages IgE production homeostasis, facilitated antigen presentation, and IgE transportation through airway and gut epithelial cells.²

Recently, research into anti-IgE antibodies as therapy for allergy and asthma has been increasing, with antibodies being designed to target free IgE and membrane-bound IgE. As of now, the monoclonal antibody omalizumab is the only licensed anti-IgE therapy available for clinical use in allergic asthma and chronic spontaneous urticaria. Other drugs in development include ligelizumab, which demonstrates improvements to IgE binding, production and basophil activation compared to omalizumab. Furthermore, IgE antibody MOv18 has shown potential for cancer therapy.⁴

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References:

1. Schroeder, H. W., & Cavacini, L. (2010). Structure and Function of Immunoglobulins. The Journal of Allergy and Clinical Immunology, 125(2 0 2), S41. https://www.jacionline.org/article/S0091-6749(09)01465-1/fulltext

2. Godwin, L., Sinawe, H., & Crane, J. S. (2022). Biochemistry, Immunoglobulin E. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK541058/

3. Gasser, P., Tarchevskaya, S. S., Guntern, P., Brigger, D., Ruppli, R., Zbären, N., Kleinboelting, S., Heusser, C., Jardetzky, T. S., & Eggel, A. (2020). The mechanistic and functional profile of the therapeutic anti-IgE antibody ligelizumab differs from omalizumab. Nature Communications 2020 11:1, 11(1), 1–14. https://www.nature.com/articles/s41467-019-13815-w

4. Spicer, J., Basu, B., Montes, A., Banerji, U., Kristeleit, R., Miller, R., Veal, G. J., Corrigan, C. J., Till, S. J., Figini, M., Canevari, S., Barton, C., Jones, P., Mellor, S., Carroll, S., Selkirk, C., Nintos, G., Kwatra, V., Funingana, I. G., … Karagiannis, S. N. (2023). Safety and anti-tumour activity of the IgE antibody MOv18 in patients with advanced solid tumours expressing folate receptor-alpha: a phase I trial. Nature Communications 2023 14:1, 14(1), 1–11. https://www.nature.com/articles/s41467-023-39679-9