RADIOIMMUNOASSAY FOR HUMAN THYMUS-LEUKEMIA-ASSOCIATED ANTIGEN

A competitive radioimmunoprecipitation method was developed for the quantitation of human thymus-leukemia-associated antigen (HThy-L) isolated from human thymus tissue. Antisera to the antigen were raised by immunization of rabbits with purified fractions of HThy-L. The antigen was labeled with 1251 by means of a modification of the lactoperoxidase technique and subjected to Sephadex G-100 gel filtration. Analysis of fractions eluted from this column by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed two labeled compo-nents with apparent molecular weights of 45, 000 and 25, 000 daltons, respectively. Immunoprecipitation with anti-HThy-L anti-serum demonstrated directly that the 45, 000-dalton component carried HThy-L antigenicity. This fraction served as the source of labeled antigen in a competitive radioimmunoassay that permitted the detection of approximately 1 ng HThy-L. With the use of this assay, we confirmed quantitatively that the highest amounts of HThy-L were found in extracts of thymocytes, normal thymus tissues, and lymphoblasts from T-cell lines.-J Natl Cancer Inst 62: 465-470, 1979. © 1979 Oxford University Press. All rights reserved.