Activated T-lymphocytes express class I molecules which are hyposialylated compared to other lymphocyte populations.

Various H-2 and Qa/Tla region encoded class I glycoproteins expressed on the surface of resting and activated T- and B-lymphocytes were compared by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). The isoelectrophoretic patterns of the H-2K, H-2D, Qa-2 and Qa-1 molecules isolated from activated T-lymphocytes were more isoelectrically heterogeneous and/or possessed species with a more basic pI than the same molecules isolated from resting T- and B-cells or activated B-lymphocytes. The differences in charge heterogeneity of class I molecules between activated T-cells and the other cell subpopulations were abolished by treatment with: (1) endoglycosidase F which removes N-linked oligosaccharides from glycoproteins, and (2) neuraminidase which removes sialic acids from carbohydrate side chains. Thus, the increased charged heterogeneity of class I molecules expressed by activated T-cells is due to altered sialylation of their N-linked oligosaccharides. These results indicate that a mechanism exists, upon activation of T-lymphocytes, for alteration (desialylation) of the carbohydrate moieties of class I molecules.