Department of Biochemistry, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan.
Devision of Human Life Science, Fukushima Medical University School of Nursing, Fukushima 960-1295, Japan.
Molecules. 2018 May 30;23(6):1314. doi: 10.3390/molecules23061314.
Antibodies are useful for detecting glycoprotein antigens, but a conventional antibody recognizes only a protein epitope rather than a glycan. Thus, glycan isoform detection generally requires time- and labor-consuming processes such as lectin affinity column chromatography followed by sandwich ELISA. We recently found antigen-antibody reactions that were inhibited by lectin binding to glycans on the glycoprotein antigen, leading to a convenient glycoform-specific assay. Indeed, agglutinin (SSA) lectin, a binder to sialylα2,6galactose residue, inhibited antibody binding to α2,6-sialylated transferrin (Tf) (SSA inhibition). SSA inhibition was not observed with other glycoforms, such as periodate-treated, sialidase-treated and sialidase/galactosidase-treated Tf, suggesting that the assay was glycoform-specific. SSA inhibition was also applicable for visualizing localization of α2,6-sialylated-Tf in a liver section. This is the first immunohistochemical demonstration of glycoform localization in a tissue section. SSA inhibition was utilized for establishing ELISA to quantify α2,6-sialylated carcinoembryonic antigen (CEA), a marker for various cancers. In addition, α2,6-sialylated-CEA was visualized in a colonic adenocarcinoma section by SSA inhibition. The method would further be applicable to a simple and rapid estimation of other α2,6-sialylated glycoproteins and have a potential aid to histopathological diagnosis.
抗体可用于检测糖蛋白抗原，但常规抗体仅能识别蛋白质表位而非糖基。因此，糖型检测通常需要耗时耗力的过程，如凝集素亲和柱层析，然后是夹心 ELISA。我们最近发现了一种抗原-抗体反应，该反应被凝集素与糖蛋白抗原上的糖基结合所抑制，从而产生了一种方便的糖型特异性检测方法。事实上，凝集素（SSA），一种与唾液酸α2,6-半乳糖残基结合的凝集素，抑制了抗体与α2,6-唾液酸化转铁蛋白（Tf）（SSA 抑制）的结合。其他糖型，如过碘酸盐处理、唾液酸酶处理和唾液酸酶/半乳糖酶处理的 Tf，并没有观察到 SSA 抑制，表明该检测方法是糖型特异性的。SSA 抑制也适用于可视化肝组织切片中α2,6-唾液酸化-Tf 的定位。这是首次在组织切片中进行糖型定位的免疫组织化学证明。SSA 抑制被用于建立 ELISA 来定量α2,6-唾液酸化癌胚抗原（CEA），这是各种癌症的标志物。此外，SSA 抑制还可以在结肠腺癌切片中观察到α2,6-唾液酸化-CEA。该方法还可进一步应用于其他α2,6-唾液酸化糖蛋白的简单快速估计，并有可能辅助组织病理学诊断。
