Local adoptive transfer to mice of human delayed hypersensitivity: reactions by the radioisotopic footpad assay.

Human delayed hypersensitivity to living BCG organisms and/or Varidase was adoptively transferred to mice and assayed in mice by a radioisotope footpad assay (FPA). A mixture of the antigen and peripheral blood lymphocytes from patients (positive skin reactions to PPD and/or Varidase) or healthy volunteers was inoculated into the footpads of lethally X-irradiated mice. A positive footpad reaction was accompanied by an increased leakage of the radiolabelled serum protein from the blood stream into the intercellular space at the site of inoculation, and was measured by the 'foot-count ratio', or radioactivity in the test foot divided by radioactivity in the contralateral foot. The intensity of the footpad reaction correlated directly with the skin test response of the human lymphocyte donors.