Comparison of thymic and peripheral T cell Ly‐2/3 antigens

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Abstract
Major structural differences occur between the thymic and peripheral T cell forms of the Ly‐2/3 antigen. Thymus Ly‐2/3 consists of similar amounts of two types of disulfide‐linked heterodimer, αβ and α′β (Mra = 38000, Mra′ = 35000, Mrβ = 30000). In contrast material from peripheral T cells consists almost exclusively of αβ dimers. The α chains of thymus and peripheral T cells differ also in isoelectric point with the thymic α chain being the more acidic. Based on peptide mapping experiments the α and α′ chains of thymus are likely to be alternatively modified forms of the same polypeptide backbone. Individual T cell clones or T cell tumors propagated in vitro exhibit either a typical thymus or a typical peripheral T cell Ly‐2/3 polypeptide pattern indicating that the synthesis of both α and α′ chains can occur in the same cell. The heterogeneity of thymic Ly‐2/3 can be considerably reduced by removal of sialic acid residues, and after desialylation the α chains of thymus and a cloned cytotoxic T lymphocyte (CTL) line cannot be electrophoretically distinguished. If Ly‐2 structures affected the antigen specificity of CTL, a different structural variant would be expected in individual clones. The electrophoretic identity of desialylated thymus and CTL α chains suggests that Ly‐2 does not exhibit clonal variation in polypeptide structure and, therefore, cannot contribute to antigen specificity.

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