An Indirect Radioimmunoassay for Thymus Leukemia (TL) Antigens¹

An indirect radioimmunassay for thymus leukemia (TL)² antigens has been developed and its specificity documented. The assay makes use of anti-TL antibodies produced in congenic mice (A-Tla^b) and radioiodinated purified rabbit anti-mouse IgG. Using this assay, differences can be detected in the amounts of antigen expressed on thymocytes of the three known phenotypes (TL.1,2,3; TL.2; TL^-) of inbred mouse strains. Significant differences are also detected in comparison of the thymocytes from homozygous TL.1,2,3 mice (A-Tla^a) and heterozygotes from Tla^a and Tla^b parents. Optimum conditions for the assay have been established. Its ability to detect antigens on glutaraldehyde-fixed cells and the binding of noncytolytic antibodies on both viable and fixed cells are documented. The assay has also been used to quantitate the changes in TL antigen expression on cells incubated in anti-TL antisera under conditions of antigenic modulation.