Germinal center marker GL7 probes activation-dependent repression of N-glycolylneuraminic acid, a sialic acid species involved in the negative modulation of B-cell activation.
Sialic acid (Sia) is a family of acidic nine-carbon sugars that occupies the nonreducing terminus of glycan chains. Diversity of Sia is achieved by variation in the linkage to the underlying sugar and modification of the Sia molecule. Here we identified Sia-dependent epitope specificity for GL7, a rat monoclonal antibody, to probe germinal centers upon T cell-dependent immunity. GL7 recognizes sialylated glycan(s), the alpha2,6-linked N-acetylneuraminic acid (Neu5Ac) on a lactosamine glycan chain(s), in both Sia modification- and Sia linkage-dependent manners. In mouse germinal center B cells, the expression of the GL7 epitope was upregulated due to the in situ repression of CMP-Neu5Ac hydroxylase (Cmah), the enzyme responsible for Sia modification of Neu5Ac to Neu5Gc. Such Cmah repression caused activation-dependent dynamic reduction of CD22 ligand expression without losing alpha2,6-linked sialylation in germinal centers. The in vivo function of Cmah was analyzed using gene-disrupted mice. Phenotypic analyses showed that Neu5Gc glycan functions as a negative regulator for B-cell activation in assays of T-cell-independent immunization response and splenic B-cell proliferation. Thus, Neu5Gc is required for optimal negative regulation, and the reaction is specifically suppressed in activated B cells, i.e., germinal center B cells.
Naito
Yuko
Y
Laboratory of Membrane Biochemistry and Biophysics, Graduate School of Biostudies, Kyoto University, Yoshida-shimoadachi, Sakyo-ku, Kyoto 606-8501, Japan.
Takematsu
Hiromu
H
Koyama
Susumu
S
Miyake
Shizu
S
Yamamoto
Harumi
H
Fujinawa
Reiko
R
Sugai
Manabu
M
Okuno
Yasushi
Y
Tsujimoto
Gozoh
G
Yamaji
Toshiyuki
T
Hashimoto
Yasuhiro
Y
Itohara
Shigeyoshi
S
Kawasaki
Toshisuke
T
Suzuki
Akemi
A
Kozutsumi
Yasunori
Y
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology*; D016466:CHO Cells; D049109:Cell Proliferation; D006224:Cricetinae; D003412:Cricetulus; D000939:Epitopes / Q000276:immunology; D018390:Gene Targeting; D018858:Germinal Center / Q000276:immunology*; D006801:Humans; D037102:Lectins / Q000378:metabolism; D008024:Ligands; D008213:Lymphocyte Activation / Q000276:immunology*; D051379:Mice; D006899:Mixed Function Oxygenases / Q000172:deficiency / Q000235:genetics; D019158:N-Acetylneuraminic Acid / Q000378:metabolism*; D009438:Neuraminic Acids / Q000378:metabolism*; D019000:Phosphotyrosine / Q000378:metabolism; D011134:Polysaccharides / Q000378:metabolism; D051381:Rats; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism; D063265:Sialic Acid Binding Immunoglobulin-like Lectins; D012799:Sialyltransferases / Q000378:metabolism; D013154:Spleen / Q000276:immunology; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase
D000911:Antibodies, Monoclonal; D000939:Epitopes; D037102:Lectins; D008024:Ligands; D009438:Neuraminic Acids; D011134:Polysaccharides; D011947:Receptors, Antigen, B-Cell; D063265:Sialic Acid Binding Immunoglobulin-like Lectins; C032592:N-glycolylneuraminic acid; D019000:Phosphotyrosine; D006899:Mixed Function Oxygenases; C074383:CMPacetylneuraminate monooxygenase; D012799:Sialyltransferases; D019158:N-Acetylneuraminic Acid; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase