Interrelationships of the "Ly-6 complex" antigens.

Competitive binding studies and immunoprecipitation experiments define at least five distinct epitopes encoded by Ly-6-linked genes--Ly-6A.2, Ly-6B.2, Ly-6C.2, Ly-6D.2, and ThB. Ly-6A.2, a 33 kd protein, and Ly-6D.2 are closely overlapping epitopes that can be distinguished by their unique thymus reactions of 10-20% or greater than 90%, respectively. Similarly, the Ly-6C.2 antigen present on a 14 kd moiety loosely overlaps the Ly-6B.2 antigen. Ly-6C.2 and Ly-6B.2 antigens are distinct from Ly-6A.2 and Ly-6D.2, however. ThB is a 16-18 kd antigen which is not associated on the cell surface with any other "Ly-6" antigens. In addition, independently derived antibodies made to the Ly-6C.2 antigen detect an identical epitope, as do antibodies to Ly-6A.2 and Ly-6B.2. These results imply the existence of a single antigenic site on each of these molecules.