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
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
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DOI：
10.1128/mcb.02047-06
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发表时间：
2007-04-01
影响因子：
5.3
通讯作者：
Kozutsumi, Yasunori
中科院分区：
文献类型：
--
作者：
Naito, Yuko;Takematsu, Hiromu;Kozutsumi, Yasunori
唾液酸（Sia）是占据聚糖链的非还原末端的酸性九碳糖家族。Sia的多样性是通过与潜在糖的连接的变化和Sia分子的修饰来实现的。在这里，我们确定了Sia依赖性表位特异性GL 7，大鼠单克隆抗体，探测germination中心后T细胞依赖性免疫。GL 7以Sia修饰依赖性和Sia连接依赖性方式识别唾液酸化聚糖，即乳糖胺聚糖链上的α 2，6-连接的N-乙酰神经氨酸（Neu 5Ac）。在小鼠生殖中心B细胞中，由于CMP-Neu 5Ac羟化酶（Cmah）的原位抑制，GL 7表位的表达上调，Cmah是负责Sia将Neu 5Ac修饰为Neu 5Gc的酶。这种Cmah抑制导致CD 22配体表达的活化依赖性动态减少，而不失去生发中心的α 2，6-连接的唾液酸化。使用基因破坏小鼠分析Cmah的体内功能。表型分析表明，Neu 5Gc聚糖在T细胞非依赖性免疫应答和脾B细胞增殖试验中作为B细胞活化的负调节剂发挥作用。因此，Neu 5Gc是最佳负调控所必需的，并且该反应在活化的B细胞中被特异性抑制，即，生发中心B细胞。
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 alpha 2,6-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 alpha 2,6-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.