Identification of Cell Surface Straight Chain Poly-N-Acetyl-Lactosamine Bearing Protein Ligands for VH4-34-Encoded Natural IgM Antibodies
Identification of Cell Surface Straight Chain Poly-N-Acetyl-Lactosamine Bearing Protein Ligands for VH4-34-Encoded Natural IgM Antibodies
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DOI：
10.4049/jimmunol.1501697
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发表时间：
2015-12-01
影响因子：
4.4
通讯作者：
Teng, Nelson N. H.
中科院分区：
文献类型：
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作者：
Bhat, Neelima M.;Adams, Christopher M.;Teng, Nelson N. H.
已充分记载了IgM同种型的人VH 4 -34编码的Ab的B细胞结合和细胞毒性。AVH 4 -34-IgM最近在治疗B细胞急性淋巴细胞白血病的1期试验中显示出有利的早期反应。尽管其B细胞配体已被鉴定为直链聚-N-乙酰-乳糖胺（SC-PNAL），但糖部分的载体尚未被鉴定。使用纳米电喷雾电离质谱，我们确定了CD 147-CD 98的代谢活化相关蛋白复合物作为人前B细胞系Nalm-6上聚-N-乙酰-乳糖胺（SC-PNAL）的主要载体。先前的研究已经表明CD 45作为VH 4 -34编码的IgG Ab的SC-PNAL载体。因为Nalm-6是CD 45阴性的，所以检测了具有高CD 45表达的人外周血B淋巴细胞和人B细胞系Reh的SC-PNAL载体蛋白。Western印迹分析显示，CD 147 -98复合物确实被来自人外周血B淋巴细胞和人B细胞系Reh、OCI-Ly 8和Nalm-6的VH 4 -34编码的IgM免疫沉淀。然而，CD 45仅从外周B淋巴细胞免疫沉淀，而不是从Reh，尽管CD 45的高表达。这些结果表明，人B细胞在CD 147 -98复合物上保留SC-PNAL，但调节CD 45上的糖部分。由于碳水化合物部分可以作为选择性抗原的VH 4 -34自身抗体库，其差异表达的蛋白质可能会提供一个线索，复杂的非典型调控的VH 4 -34基因。
B cell binding and cytotoxicity by human VH4-34-encoded Abs of the IgM isotype has been well documented. AVH4-34-IgM has recently shown a favorable early response in a phase 1 trial for treatment of B cell acute lymphoblastic leukemia. Although its B cell ligand has been identified as straight chain poly-N-acetyl-lactosamine (SC-PNAL), the carrier of the sugar moiety has not been identified. Using nanoelectrospray ionization mass spectrometry, we identify the metabolic activation related protein complex of CD147-CD98 as a major carrier of poly-N-acetyl-lactosamine (SC-PNAL) on human pre-B cell line Nalm-6. Previous studies have suggested CD45 as the SC-PNAL carrier for VH4-34-encoded IgG Abs. Because Nalm-6 is CD45 negative, human peripheral blood B lymphocytes and human B cell line, Reh, with high CD45 expression, were examined for SC-PNAL carrier proteins. Western blot analysis shows that the CD147-98 complex is indeed immunoprecipitated by VH4-34-encoded IgMs from human peripheral blood B lymphocytes and human B cell lines, Reh, OCI-Ly8, and Nalm-6. However, CD45 is immunoprecipitated only from peripheral B lymphocytes, but not from Reh despite the high expression of CD45. These results suggest that human B cells retain SC-PNAL on the CD147-98 complex, but modulate the sugar moiety on CD45. Because the carbohydrate moiety may act as a selecting Ag for VH4-34 autoantibody repertoire, its differential expression on proteins may provide a clue to the intricate atypical regulation of the VH4-34 gene.