Shared idiotypic determinants on B and T lymphocytes reactive against the same antigenic determinants. V. Biochemical and serological characteristics of naturally occurring, soluble antigen-binding T-lymphocyte-derived molecules.
Normal rat lymphocyte populations house a high percentage of lymphocytes with idiotypic, antigen-binding receptors for the major histocompatibility complex antigens of the rat. These receptors can be isolated from normal serum or lymphocyte supernatants. Idiotypic, antigen-binding molecules released from normal Lewis lymphocytes were thus isolated using anti-(Lewis anti-DA) immuno adsorbents. Analysis by SDS polyacrylamide electrophoresis using molecules labeled by external or internal means (125I or 3H) demonstrated that B lymphocytes produce molecules of 'conventional' 7S-8S IgM type. T-lymphocyte-derived molecules had a molecular weight of around 150,000 and consisted of two chains of similar size. Such single chains would succumb to proteolysis by normal serum factors to yield fragments in the size range of 30,000-40,000 daltons. All three groups of T-cell-derived molecules expressed both antigen-binding and idiotypic markers. No evidence was obtained that any light chains are linked to the T-receptor molecules. Serological analysis of the T-cell molecules failed to prove the existence of any determinants of constant immunoglobulin type, nor did these molecules express antigenic markers of major histocompatibility complex types.