LIGAND-SPECIFIC OLIGOMERIZATION OF T-CELL RECEPTOR MOLECULES

T cells initiate many immune responses through the interaction of thei r T-cell antigen receptors (TCR) with antigenic peptides bound to majo r histocompatibility complex (MHC) molecules, This interaction sends a biochemical signal into the T cell by a mechanism that is not clearly understood. We have used quasielastic light scattering (QELS) to show that, in the presence of MHC molecules bound to a full agonist peptid e, TCR/peptide-MHC complexes oligomerize in solution to form supramole cular structures at concentrations near the dissociation constant of t he binding reaction. The size of the oligomers is concentration depend ent and is calculated to contain two to six ternary complexes for the concentrations tested here. This effect is specific as neither molecul e forms oligomers by itself, nor were oligomers observed unless the co rrect peptide was bound to the MHC. These results provide direct evide nce for models of T-cell signalling based on the specific assembly of multiple TCR/peptide-MHC complexes(1-4) in which the degree of assembl y determines the extent and qualitative nature of the transduced signa l(5). They may also explain how T cells maintain sensitivity to antige ns present in only low abundance on the antigen-presenting cell.