Enrichment of Sialylated IgG by Lectin Fractionation Does Not Enhance the Efficacy of Immunoglobulin G in a Murine Model of Immune Thrombocytopenia

Intravenous immunoglobulin G (IVIg) is widely used against a range of clinical symptoms. For its use in immune modulating therapies such as treatment of immune thrombocytopenic purpura high doses of IVIg are required. It has been suggested that only a fraction of IVIg causes this anti immune modulating effect. Recent studies indicated that this fraction is the Fc-sialylated IgG fraction. The aim of our study was to determine the efficacy of IVIg enriched for sialylated IgG (IVIg-SA (+)) in a murine model of passive immune thrombocytopenia (PIT). We enriched IVIg for sialylated IgG by Sambucus nigra agglutinin (SNA) lectin fractionation and determined the degree of sialylation. Analysis of IVIg-SA (+) using a lectin-based ELISA revealed that we enriched predominantly for Fab-sialylated IgG, whereas we did not find an increase in Fc-sialylated IgG. Mass spectrometric analysis confirmed that Fc sialylation did not change after SNA lectin fractionation. The efficacy of sialylated IgG was measured by administering IVIg or IVIg-SA (+) 24 hours prior to an injection of a rat anti-mouse platelet mAb. We found an 85% decrease in platelet count after injection of an anti-platelet mAb, which was reduced to a 70% decrease by injecting IVIg (p

静脉注射免疫球蛋白G（Intravenous immunoglobulin G, IVIg）被广泛用于缓解多种临床症状。在免疫调节治疗（如免疫性血小板减少症（immune thrombocytopenic purpura）的治疗）中，需使用大剂量IVIg。有研究表明，仅IVIg中的部分组分可发挥此类抗免疫调节效应。近期研究指出，该活性组分为Fc唾液酸化IgG（Fc-sialylated IgG）。本研究旨在探究富集唾液酸化IgG的IVIg（IVIg-SA (+)）在被动性免疫性血小板减少症（passive immune thrombocytopenia, PIT）小鼠模型中的疗效。我们通过接骨木凝集素（Sambucus nigra agglutinin, SNA）分级分离法对IVIg进行唾液酸化IgG富集，并检测了唾液酸化程度。基于凝集素的酶联免疫吸附试验（lectin-based ELISA）对IVIg-SA (+)的分析结果显示，我们主要富集得到了Fab唾液酸化IgG（Fab-sialylated IgG），未检测到Fc唾液酸化IgG的水平升高。质谱分析（mass spectrometric analysis）证实，经SNA凝集素分级分离后，IgG的Fc唾液酸化程度未发生改变。我们通过在注射大鼠抗小鼠血小板单克隆抗体（rat anti-mouse platelet mAb）前24小时给予IVIg或IVIg-SA (+)，评估唾液酸化IgG的疗效。结果显示，注射抗血小板单克隆抗体后，小鼠血小板计数下降了85%；预先给予IVIg可将该下降幅度降至70%（p