Antigen-Binding Thymic Lymphocytes: Specific Binding of Soluble Antigen Molecules and Quantitation of Surface Receptor Sites

Abstract

Abstract Lymphocytes binding hemocyanin (KLH) have been studied in the thymus and spleen of unimmunized mice. There is a small population of thymic cells which specifically binds KLH—unrelated antigens do not block the binding. A comparison was made of techniques to detect antigen-binding cells. The presence of an antibody to the cell-bound antigen favored the detection of antigen bound to the T cell surface. Quantitation of antigen bound to spleen and thymus cells was determined immunochemically. Spleen cells bind about five times more antigen than thymic cells. Anti-Ig antibodies did not affect consistently the binding of antigen to thymic cells but reduced significantly that bound to spleen cells. We conclude that thymic cells have lower receptor density than spleen cells (3/4 of which may be B lymphocytes) and that this lower receptor density may explain the lower binding strength of the T cell receptor.