The actions of leukocyte dialysate were recognized for the first time in 1942 when Karl Landsteiner (discoverer of human blood group antigens and antibodies, 1900, Nobel Prize winner, 1930) and M.V. Chase accomplished a transfer of the delayed hypersensitivity response of sensitized guinea pigs to the non-sensitized ones by transplanting live guinea pig leukocytes. The same experiment was repeated in 1949 when H.S. Lawrence succeeded to transfer tuberculin hypersensitivity from sensitized donors to non-sensitized human volunteers. He collected leukocytes from immune donors who demonstrated a positive skin reaction to a specific antigen and prepared extracts from them. He injected the extracts to skin test negative or immune compromised subjects. Subsequently the recipients reverted to skin positive reactions to the same antigens. These experiments thus provided direct and dramatic evidence for transfer of systemic and specific immunity between individuals.

H.S. Lawrence proved in 1955 that such property is retained also by a purified leukocyte extract; and named the effective component of such extract a “transfer factor” (TF). In those days the claims of H.S. Lawrence about the transfer of ability to respond by delayed skin hypersensitivity via a soluble factor of molecular weight lower than 20,000 D (Dalton) were considered ‘quackery’. The dominant theories of those times declared that all immune reactions, including delayed skin hypersensitivity, were dependent on antibodies of molecular weight at least 150,000 D. In 1963 H.S. Lawrence discovered that the ability to respond to an immunogen is retained by a leukocyte extract of molecular weight under 10,000 D.

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