T cell activation results in physical modification of the mouse CD8 beta chain

The T lymphocyte glycoprotein, CD8, is an essential component of the response of class I MHC-restricted T cells to Ag. CD8 is expressed on the surface of class I-restricted T cells as disulfide-bonded heterodimers and higher multimers of two distantly related polypeptides, alpha and beta. The CD8 alpha polypeptide, expressed in transfection studies as homodimers, is able to reproduce both the adhesive and stimulatory properties of CD8, leaving the function of the CD8 beta polypeptide unresolved. Herein we demonstrate that the CD8 beta polypeptide changes physically during T cell maturation and activation by reversibly altering its sialic acid content. These changes occur specifically on CD8 beta not -alpha, indicating that the primary role of the CD8 beta chain may be regulatory, influencing the physical structure of the CD8 complex, and suggesting a novel mechanism of controlling receptor/ligand interactions.