What is "transfer factor"

Transfer factors are essentially small immune messenger molecules that are produced by all higher organisms. They are an ancient part of the immune system and represent "an archaic dialect in the language of cells." Transfer factors were originally described as immune molecules that are derived from blood or spleen cells that cause antigen-specific cell-mediated immunity, primarily delayed hypersensitivity and the production of lymphokines, as well as binding to the antigens themselves. They have a molecular weight of approximately 5000 Daltons and are composed entirely of amino acids. Transfer factors were discovered by Henry Sherwood Lawrence in 1954.

A second use of the term transfer factor applies to a likely different entity derived from cow colostrum or chicken egg yolk which is marketed as an oral dietary supplement under the same name citing claims of benefit to the immune system.