Specific anti-Ly-1.1 serum was used in conjunction with fixed Staphylococcus aureus (Cowan I strain) to precipitate labeled material from NP-40 extracts of mouse thymocytes labeled with 125I by using lactoperoxidase and with NaB3H4 by using galactose oxidase. Thymocytes from the congenic strains C57BL/6-Ly-1a (Ly-1.1-positive) and C57BL/6J (Ly-1.2-positive) were used as sources of labeled antigens and as immune absorbents so that the Ly-1.1 alloantigen could be studied in the absence of genetic background differences. Results of SDS-PAGE under reducing conditions suggest that the Ly-1.1 antigenic determinant(s) may be associated with a glycoprotein of apparent m.w. 67,000 which is labeled by both labeling methods and/or with a component with an apparent m.w. of 87,000 that was labeled with NaB3H4 and galactose oxidase but not with 125I. It is not known whether one or both of these molecular species or an unlabeled species associated with them is the target of the Ly-1.1-specific cytotoxic antibodies. In addition, results of SDS-PAGE under nonreducing conditions suggest that the component with apparent m.w. 67,000 is not involved in intermolecular disulfide bonds.

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This work was supported by United States Public Health Service Research Grant CA 15808 from the National Cancer Institute to Paul D. Gottlieb and by United States Public Health Service Research Grant CA 14051 from the National Cancer Institute to the Massachusetts Institute of Technology Center for Cancer Research.

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