Polyclonal IgY is the major circulating antibody type found in serum and egg yolks of chickens. In the serum, IgY is mixed with other antibody isotypes, including IgM. Egg yolks, however, contain only antibodies of the IgY type; moreover, they contain these antibodies in high concentrations – about twice that of the concentrations found in serum.

There is only one isoform of IgY. This makes it unlike IgG, which arises from multiple gamma heavy chain isotypes, including IgG1, IgG2a, and others. Like mammalian IgG, however, chicken IgY consists of two heavy and two light chains and contain two antigen binding domains.

Although it features some minor physicochemical differences, in terms of thermal- and acid-stability, when compared with rabbit IgG, chicken IgY can be used in all of the same research applications, including Western Blot, Immunohistochemistry, Immunocytochemistry, Immunoprecipitation, ELISA and protein microarrays.