A M I C Acid 60 - L - Alanine 30 - L - Tyrosine 10 ( Gat ) by Craig

B lymphocytes and certain subpopulations of T lymphocytes respond to stimulation with antigen by synthesis and secretion of unique glycoproteins capable of binding the stimulating antigen. In the case of the B cell, these glycoproteins are the classic antibody molecules, which have been well characterized in terms of structure, function, and organization, both at the protein and nucleic acid levels. The antibody nature of the B cell receptor for antigen is also well documented (1, 2). The equivalent molecule(s) that serve as T cell receptors for antigen or are secreted by T cells in response to antigen are not as well characterized. Recently, however, several laboratories have reported (3-5) initial characterization of putative T cell receptors for antigen on helper and cytotoxic T cells. Also partially characterized are those biologically active molecules synthesized and secreted by suppressor T (Ts) z cells, the suppressor T cell factors (TsF). Structural characterization of these secreted molecules and their relationship to receptors for antigen on Ts cells is still incomplete, and largely descriptive in nature (6-1 1), however, it is known (12) that Ts cells do not use the fl chain of the T cell receptor used by helper and cytotoxic T ceils. In spite of the inherent difficulties in studying TsF molecules, which have very high biological activity in very small quantities of material (~ 10 TM units of suppressor activity per nanogram of protein), certain facts concerning their structural organization have emerged from a variety of systems where TsF have been derived from T cell hybridomas. The T cell-derived molecules specific for the synthetic antigen, Lglutamic acid60-L-alanine30-L-tyrosinel0 (GAT) are composed of either one or two polypeptide chains, depending on their cellular source (9), and are relatively hydrophobic molecules (8, 10, 1 1) ,that serologically crossreact with serum antibody against the same antigen when analyzed with antiidiotypic antibody