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Abstract
The present studies were undertaken in order to (a) verify the presence of a human Thy 1 antigen, (b) demonstrate its similarity to murine Thy 1, and (c) biochemically characterize the molecule.
Previously, a 25,000 molecular weight molecule had been isolated from a human T lymphoblastoid cell line, Molt 3, using isolation procedures most frequently used for the isolation of rodent Thy 1. The human Thy 1 (p25) was demonstrated to be biochemically similar to murine Thy 1.2 by molecular weight and ability to bind Lens Culinaris lentil lectin. Recently, we confirmed similarity between the murine and the human molecule by peptide maps and amino acid compositions. In addition, a strong cross-reactivity using an anti-p25 antiserum was established with human IgG subclasses. The antiserum did not react with human IgM or IgA, nor with primate immunoglobulins or a battery of other antigens. Through a variety of immunoabsorption experiments, through the use of various digestions, and known amino acid sequences, the shred areas of homology were tentatively determined to be in the intact disulfide bonds of the first and third domains of human IgG and the 9-112 disulfide bond of Thy 1.
A form of the p25 antigen noted and partially characterized was the p40 antigen, the dimerized form of the p25. The p25 and p40 are essentially identical in several aspects, such as amino acid compositions, peptide maps, carbohydrate compositions, reactivity to anti-p25 serum, and in aggregation studies. It was determined that the detergent sodium dodecyl sulfate tends to convert the p25 molecule into the p40 form through some other chemical means than disulfide bond interchange. The method of isolation and reagents used unequivocally determines observed molecular weight.
Another form detected is the p16 which also reacted with anti-p25 serum, was similar by amino acid composition, slightly different by peptide mapping and definitely contained less carbohydrate than the p25 antigen. The p16 is possibly a cryptic antigen, a breakdown form of the p25 molecule.
A 40,000 MW molecule was isolated from human thymus which binds lentil lectin, reacts with antiserum made to the p25 antigen and possesses an amino acid composition very similar to that of the p25 antigen. Data suggests that the Thy 1 antigen from human thymocytes tends to dimerize more readily than that found on Molt 3 cells and that this antigen is present in considerably smaller amounts on human thymocytes as compared with Molt 3 cells.
