Immunoglobulin Y (abbreviated asIgY) is a type ofimmunoglobulin which is the major antibody inbird,reptile, andlungfishblood. It is also found in high concentrations in chicken eggyolk. As with the other immunoglobulins, IgY is a class ofproteins which are formed by theimmune system in reaction to certain foreign substances, and specifically recognize them.
IgY is often mislabelled asImmunoglobulin G (IgG) in older literature, and sometimes even in commercial product catalogues, due to its functional similarity to mammalian IgG andImmunoglobulin E (IgE). However, this older nomenclature is obsolete, since IgY differs both structurally and functionally from mammalian IgG,[1] and does not cross-react with antibodies raised against mammalian IgG.[2]
Since chickens can lay eggs almost every day, and the yolk of an immunised hen's egg contains a high concentration of IgY, chickens are gradually becoming popular as a source of customised antibodies for research. (Usually, mammals such as rabbits or goats are injected with theantigen of interest by the researcher or a contract laboratory.)[3]
Ducks produce a truncated form of IgY which is missing part of the Fc region. As a result, it cannot bindcomplement or be picked up bymacrophages.[4][5]
IgY has also been analyzed in the Chinese soft-shelled turtle,Pelodiscus sinensis.[6]
In chickens, immunoglobulin Y is the functional equivalent toImmunoglobulin G (IgG). Like IgG, it is composed of two light and two heavy chains. Structurally, these two types of immunoglobulin differ primarily in the heavy chains, which in IgY have amolecular mass of about 65,100atomic mass units (amu), and are thus larger than in IgG. The light chains in IgY, with amolar mass of about 18,700 amu, are somewhat smaller than the light chains in IgG. The molar mass of IgY thus amounts to about 167,000 amu. The steric flexibility of the IgY molecule is less than that of IgG.
Functionally, IgY is partially comparable toImmunoglobulin E (IgE), as well as to IgG. However, in contrast to IgG, IgY does not bind toProtein A, toProtein G, or to cellularFc receptors. Furthermore, IgY does not activate thecomplement system. The nameImmunoglobulin Y was suggested in 1969 by G.A. Leslie and L.W. Clem, after they were able to show differences between the immunoglobulins found in chicken eggs, and immunoglobulin G. Other synonymous names areChicken IgG,Egg Yolk IgG, and7S-IgG.
As compared to mammalian antibodies, IgY offers various advantages for the targeted extraction ofantibodies and their application inbioanalysis. Since the antibodies are extracted from the yolks of laid eggs, the method of antibody production is non-invasive. Thus, no blood must be taken from the animals for the extraction of blood serum.
The available quantity of a given antibody is considerably increased through repeated egg laying from the same hen. Thecross-reactivity of IgY with proteins frommammals is also markedly less than that of IgG. Furthermore, theimmune response against certainantigens in chickens is more strongly expressed than inrabbits or othermammals.
Of the immunoglobulins arising during the immune response, only IgY is found in chicken eggs. Thus, in preparations from chicken eggs, there is no contamination withImmunoglobulin A (IgA) orImmunoglobulin M (IgM). The yield of IgY from a chicken egg is comparable to that of IgG from rabbit serum.
One disadvantage of IgY, as compared to mammalian antibodies, is that the isolation of IgY from egg yolk is more difficult than the isolation of IgG from blood serum. This is due in large part to the fact that IgY cannot be bound withProtein A andProtein G. Thus, it cannot be separated from other components of the assay, for example from other proteins. Additionally, the egg yolk's rich store oflipids andlipoproteins must be removed.[7] Antibody-containing blood serums, on the other hand, can sometimes be directly used in bioanalysis, i.e., without complicated isolation steps.
Particularly inAsian countries, IgY has been clinically tested as afood supplement and preservative. For example,yogurt products containing pathogen specific IgY, have been tested for their ability to reduceHelicobacter pylori in thestomach by hindering the attachment of the bacterium to the stomach lining.[8][9] The IgY used for this purpose is extracted from the eggs of immunized hens. Antibodies againstSalmonella and other bacteria, as well as againstviruses, are produced in this manner, and employed as a nutritional component for protection against thesepathogens. The Food Safety Lab ofOcean University of China has experimented with using IgY specific to the bacteriaShewanella putrefaciens andPseudomonas fluorescens as a food preservative for fish. The shelf life of fish treated with the IgY was extended from 9 days to 12 – 15 days demonstrating a significant antimicrobial activity to the specific bacteria.[10]
Anti-Fel d1 egg IgY immunoglobulin has been successfully tested to reduce activeFel d1 in cats saliva in order to lower allergenic potential of treated cats.[11]