Structural invariance of T4 molecules from T cell clones of different antigen and major histocompatibility complex specificities.

Recent studies have suggested that the T4 molecule may bind to class II major histocompatibility complex (MHC) gene products on target cells. Such an interaction could be with either a polymorphic or monomorphic determinant on class II MHC genes. The first would imply that T4 is structurally variable and represents a component of a dual receptor, whereas the latter would suggest that T4 is structurally invariant and serves as an accessory binding molecule. To resolve this question we studied the structural variability of T4 molecules isolated from four clones of differing antigen/MHC specificities. By one- and two-dimensional electrophoretic analysis and by peptide mapping, we detected no differences among the 55-kDa T4 molecules from these clones. We conclude that T4 serves as an invariant accessory binding structure and that T4 does not confer MHC specificity on T cells.