title: 9-O-Acetylation of sialomucins: a novel marker of murine CD4 T cells that is regulated during maturation and activation.
abstract: Terminal sialic acids on cell surface glycoconjugates can carry 9-O-acetyl esters. For technical reasons, it has previously been difficult to determine their precise distribution on different cell types. Using a recombinant soluble form of the Influenza C virus hemagglutinin-esterase as a probe for 9-O-acetylated sialic acids, we demonstrate here their preferential expression on the CD4 T cell lineage in normal B10.A mouse lymphoid organs. Of total thymocytes, 8-10% carry 9-O-acetylation; the great majority of these are the more mature PNA-, HSA-, and TCRhi medullary cells. While low levels of 9-O-acetylation are seen on some CD4/CD8 double positive (DP) and CD8 single positive (SP) cells, high levels are present primarily on 80- 85% of CD4 SP cells. Correlation with CD4 and CD8 levels suggests that 9-O-acetylation appears as an early differentiation marker as cells mature from the DP to the CD4 SP phenotype. This high degree of 9-O-acetylation is also present on 90-95% of peripheral spleen and lymph node CD4 T cells. In contrast, only a small minority of CD8 T cells and B cells show such levels of 9-O-acetylation. Among mature peripheral CD4 T lymphocytes, the highly O-acetylated cells are Mel 14(hi), CD44(lo), and CD45R(exon B)hi, features typical of naive cells. Digestions with trypsin and O-sialoglycoprotease (OSGPase) and ELISA studies of lipid extracts indicate that the 9-O-acetylated sialic acids on peripheral CD4 T cells are predominantly on O-linked mucintype glycoproteins and to a lesser degree, on sialylated glycolipids (gangliosides). In contrast, sialic acids on mucin type molecules of CD8 T cells are not O-acetylated; instead these molecules mask the recognition of O-acetylated gangliosides that seem to be present at similar levels as on CD4 cells. The 9-O-acetylated gangliosides on mouse T cells are not bound by CD60 antibodies, which recognize O-acetylated gangliosides in human T cells. Tethering 9-O-acetylated mucins with the Influenza C probe with or without secondary cross-linking did not cause activation of CD4 T cells. However, activation by other stimuli including TCR ligation is associated with a substantial decrease in surface 9-O-acetylation, primarily in the mucin glycoprotein component. Thus, 9-O-acetylation of sialic acids on cell surface mucins is a novel marker on CD4 T cells that appears on maturation and is modulated downwards upon activation.
authors.affiliation: Glycobiology Program, UCSD Cancer Center, the Department of Medicine, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: M
authors.initials: M
authors.lastname: Krishna
authors.forename: A
authors.initials: A
authors.lastname: Varki
mesh_terms: D000107:Acetylation; D000115:Acetylesterase; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D000944:Antigens, Differentiation, B-Lymphocyte / Q000378:metabolism; D015415:Biomarkers; D015704:CD4 Antigens / Q000032:analysis; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D016827:CD8 Antigens / Q000032:analysis; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D002265:Carboxylic Ester Hydrolases / Q000378:metabolism; D015815:Cell Adhesion Molecules; D005732:Gangliosides / Q000737:chemistry; D006389:Hemagglutinins, Viral; D009982:Gammainfluenzavirus / Q000201:enzymology; D007531:Isoflurophate / Q000494:pharmacology; D037102:Lectins; D017493:Leukocyte Common Antigens / Q000378:metabolism; D051917:Leukosialin; D008024:Ligands; D008213:Lymphocyte Activation; D051379:Mice; D008815:Mice, Inbred Strains; D009077:Mucins / Q000378:metabolism*; D051918:Sialic Acid Binding Ig-like Lectin 2; D012794:Sialic Acids / Q000378:metabolism*; D012795:Sialoglycoproteins / Q000378:metabolism; D052116:Sialomucins; D014357:Trypsin / Q000378:metabolism; D014760:Viral Fusion Proteins; D014764:Viral Proteins
chemical_list: D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; D015415:Biomarkers; D015704:CD4 Antigens; D016827:CD8 Antigens; C497868:Cd22 protein, mouse; D015815:Cell Adhesion Molecules; D005732:Gangliosides; D006389:Hemagglutinins, Viral; D037102:Lectins; D051917:Leukosialin; D008024:Ligands; D009077:Mucins; D051918:Sialic Acid Binding Ig-like Lectin 2; D012794:Sialic Acids; D012795:Sialoglycoproteins; D052116:Sialomucins; C497863:Spn protein, mouse; D014760:Viral Fusion Proteins; D014764:Viral Proteins; C060814:hemagglutinin esterase; D007531:Isoflurophate; C025676:9-O-acetyl-N-acetylneuraminic acid; D002265:Carboxylic Ester Hydrolases; D000115:Acetylesterase; C046298:sialate O-acetylesterase; D017493:Leukocyte Common Antigens; D014357:Trypsin