Immunoglobulin Y (abbreviated as IgY) is a type of immunoglobulin which is the major antibody in bird, reptile, and lungfish blood. It is also found in high concentrations in chicken egg yolk. As with the other immunoglobulins, IgY is a class of proteins which are formed by the immune system in reaction to certain foreign substances, and specifically recognize them.
IgY is often mislabelled as Immunoglobulin G (IgG) in older literature, and sometimes even in commercial product catalogues, due to its functional similarity to mammalian IgG and Immunoglobulin 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 However, this older nomenclature is obsolete, since IgY differs both structurally and functionally from mammalian IgG,[1] and does not cross-react with antibodies raised against mammalian IgG.[2]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 the antigen 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 bind complement or be picked up by macrophages.[4][5] This may be one reason ducks are less easily killed by avian influenza compared to chickens, but can still become infected and spread the virus easily.
IgY has also been analyzed in the Chinese soft-shelled turtle, Pelodiscus sinensis.[6]