Linked Glycans N of Lymphocytes Leads to Dramatic Remodeling T + and CD 8 + Activation of Murine CD 4

Differentiation and activation of lymphocytes are documented to result in changes in glycosylation associated with biologically important consequences. In this report, we have systematically examined global changes in N-linked glycosylation following activation of murine CD4 T cells, CD8 T cells, and B cells by MALDI-TOF mass spectrometry profiling, and investigated the molecular basis for those changes by assessing alterations in the expression of glycan transferase genes. Surprisingly, the major change observed in activated CD4 and CD8 T cells was a dramatic reduction of sialylated biantennary N-glycans carrying the terminal NeuGc␣2-6Gal sequence, and a corresponding increase in glycans carrying the Gal␣1-3Gal sequence. This change was accounted for by a decrease in the expression of the sialyltransferase ST6Gal I, and an increase in the expression of the galac-tosyltransferase, ␣1-3GalT. Conversely, in B cells no change in terminal sialylation of N-linked glycans was evident, and the expression of the same two glycosyltransferases was increased and decreased, respectively. The results have implications for differential recognition of activated and unactivated T cells by dendritic cells and B cells expressing glycan-binding proteins that recognize terminal sequences of N-linked glycans. D ifferentiation and activation of lymphocytes are accompanied by programmed remodeling of cell surface gly-cans of glycoproteins with biologically important consequences. Notably, the conversion of the peanut agglutinin (PNA) 5 high (PNA high) phenotype of immature CD4/CD8 medul-lary thymocytes to the PNA low phenotype of the mature single-positive CD8 and CD4 thymocytes results from conversion of the PNA ligand, the O-linked glycan Gal␤1-3GalNAc␣Thr/Ser, to its sialylated form, NeuAc␣2–3Gal␤1-3GalNAc␣Thr/Ser, that is no longer recognized by PNA due to increased expression of a sia-lyltransferase, ST3Gal I (1– 4). In CD8 T cells, this glycosylation change reduces the affinity of CD8 for MHC class I, suggesting that sialylation of CD8 O-glycans modulates CD8 function during selection and maturation of CD8 T cells (5–7). Naive CD8 cells of ST3Gal I null mice that are constitutively PNA high undergo rapid apoptosis in the periphery, reducing the CD8 population to 10% of wild type (2). Yet, conversion from PNA low to PNA high is a natural consequence of activation of wild-type CD8 cells resulting from down-regulation of ST3Gal I (2, 8, 9). In contrast, ST3Gal I is differentially regulated in activated and polarized Th1 and Th2 CD4 cells leading to the PNA high and PNA low phenotype, respectively (10). The additional increased expression of fucosyl-and sialyltransferases in Th1 cells promotes synthesis of the …