A Breif Introduction to IgY Antibody
Antibodies are important functional immunoglobulins that are produced by the immune system to fight against antigens. In humans, five antibody isotypes have been identified: IgA, IgD, IgE, IgM, and IgG. In other animals like chicken, another kind of isotype, IgY antibody, has been found.
IgY antibody is a class of immunoglobulin mainly found in birds, amphibians, and reptiles, especially in chicken egg yolk with high concentrations. Chicken IgY antibody has a similar structure and equivalent functions to that of mammalian IgG antibody. Both IgY and IgG consist of two heavy chains (HC) and two light chains (LC), of which the LCs contain a constant region and a variable region, whereas, IgY has 4 constant regions (CH1-CH4), one more than IgG with CH1-CH3. Another remarkable difference of IgY is the relatively less flexible hinge region. No hinge region is observed between CH1 and CH2 domains and interchain disulfide bonds are formed between the two CH2 domains, which limits IgY flexibility. This less flexibility, on the other hand, improves the resistance of IgY to proteolytic degradation and fragmentation. Here, the comparison between chicken IgY and mammalian IgG antibody are summarized as follows:
Table 1. Comparison of chicken IgY and mammalian IgG. (Pereira, 2019)
| Mammalian IgG antibody | Chicken IgY antibody | |
|---|---|---|
| Species | Mammals | Birds, reptiles, amphibians, and lungfish |
| Source | Serum | Serum and eggs |
| Concentration | 200 mg/bleed (40 mL) | 100-150 mg/egg (15 mL/yolk) |
| Molecular weight (kDa) | 150 | 180 |
| Constant domains in HC | 3 | 4 |
| Hinge region | Yes | No |
| Carbohydrate sidechains | 1 | 2 |
| pH stability | 2.0-11.0 | 3.5-11.0 |
| Isoelectric point | 6.1-8.5 | 5.7-7.6 |
| Heat stability | Up to 75–80°C | Up to 70°C |
| Proteolytic degradation | Pepsin, papain, trypsin, and chymotrypsin | Pepsin and papain |
| Complement binding | Yes | No |
| Rheumatoid factor binding | Yes | No |
| Fc receptor binding | Yes | No |
| Protein A/G binding | Yes | No |
Fig.1 The canonical structures of IgG and IgY. (Lee, 2017)
Therapeutic and Diagnostic Effects of IgY Antibody
Compared with commonly used IgG antibodies, the IgY antibody has drawn much attention owing to the advantages of easy generation, heat and acid resistance, high affinity, and low risk of cross-reactivity. These advantages endow IgY antibodies with great potential in diagnostic and therapeutic applications.
- Firstly and importantly, specific IgY antibodies were sensitive to detect Severe Acute Respiratory Syndrome associated coronavirus (SARS-CoV), SARS-CoV-2, and the Middle East Respiratory Syndrome coronavirus (MERS-CoV) in the animal in serum and nasopharyngeal aspirate, and provided some protection against these viruses. In addition to coronavirus, IgY antibodies also exhibited huge potential in detecting and treating other viral infections, including influenza virus, Rotavirus Group A, Hepatitis B, Dengue Fever, Ebola virus, etc.
- Secondly, chicken IgY antibodies also have been indicated to be useful in the diagnosis and treatment of bacterial, fungal, and parasitic infections, such as Salmonella typhimurium, Pseudomonas aeruginosa, Mycobacterium Tuberculosis, Candida albicans, and Trypanosoma evansi.
- Thirdly, these chicken IgY antibodies also can be developed as immunotherapeutics for the treatment of human diseases, especially in the passive immunotherapy of gastrointestinal tract infections owing to its better acid resistance.
Fig. 2 Applications of Immunoglobulin Y against SARS-CoV-2 to Inhibit COVID-19. (Lee, 2021)
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References
- Pereira, E.P.V.; et al. Egg yolk antibodies (IgY) and their applications in human and veterinary health: A review. International Immunopharmacology. 2019, 73: 293-303.
- Lee, W.; et al. Insights into the chicken IgY with emphasis on the generation and applications of chicken recombinant monoclonal antibodies. Journal of Immunological Methods. 2017, 447: 71-85.
- Lee, L.; et al. Immunoglobulin Y for Potential Diagnostic and Therapeutic Applications in Infectious Diseases. Frontiers in Immunology. 2021, 12: 696003.
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