A specific apoptotic glycosylation pattern may play an assistant or even a causative role in phagocytosis of apoptotic bodies. To elucidate the role of macrophages in lectin-mediated phagocytosis, an experimental system was used, where monocyte-derived THP-1 cells engulf the apoptotic bodies from the melanoma cell line MELJUSO. A flow cytometry assay was performed to reveal lectin expression and quantify the phagocytosis of apoptotic bodies. Taking into account that siglecs, a mannose receptor and galectins expressed on macrophages could be involved in engulfment of apoptotic bodies we studied their potential expression on THP-1 cells by means of polyacrylamide glycoconjugates. A strong binding of the cells to siglec ligands (3'SiaLac, 6'SiaLac, [Neu5Acalpha2-8]2) and galectin ligands (LacNAc, GalNAcbeta1 - 4GlcNAc, Galbeta1 - 3GalNAcbeta and asialoGM1) was observed. To reveal the corresponding targets on apoptotic bodies, the carbohydrate pattern of MELJUSO cells was analyzed. The apoptotic membrane was characterized by a high level of glycans terminated by galactose or sialic acid. To study lectin-mediated phagocytosis of apoptotic bodies by THP-1 cells, an inhibitory phagocytosis assay was performed. Binding of Galbeta1 - 3GalNAc- or LacNAc-specific reagents (lectins and antibodies) to apoptotic bodies abolished their engulfment by the THP-1 cells whereas blocking of Neu5Acalpha2 - 6 or Neu5Acalpha2 - 3 sites by the corresponding lectins was not effective. Furthermore, Galbeta1 - 3GalNAcbeta-PAA or asialoGM1-PAA binding to the THP-1 cells decreased phagocytosis, whereas two other potent THP-1-binding probes, LacNAc-PAA and GalNAcbeta1 - 4GlcNAc-PAA did not inhibit phagocytosis. Thus, Galbeta1 - 3GalNAcbeta-terminated chains represented on the apoptotic bodies but not the other tested galectin ligands appear to be a target for THP-1 cells.

中文翻译：

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Galbeta1-3GalNAcbeta结构参与THP-1细胞识别凋亡小体。

特定的凋亡糖基化模式可能在凋亡小体吞噬中起辅助作用甚至是致病作用。为了阐明巨噬细胞在凝集素介导的吞噬作用中的作用，使用了一个实验系统，其中单核细胞衍生的THP-1细胞吞噬了黑素瘤细胞系MELJUSO的凋亡小体。进行流式细胞术测定以揭示凝集素表达并定量凋亡小体的吞噬作用。考虑到在巨噬细胞上表达的单糖，甘露糖受体和半乳糖凝集素可能参与凋亡小体的吞噬，我们通过聚丙烯酰胺糖缀合物研究了它们在THP-1细胞上的潜在表达。细胞与siglec配体（3'SiaLac，6'SiaLac，[Neu5Acalpha2-8] 2）和半乳糖凝集素配体（LacNAc，GalNAcbeta1-4GlcNAc，观察到了Galbeta1-3GalNAcbeta和asialoGM1）。为了揭示凋亡小体上的相应靶标，分析了MELJUSO细胞的碳水化合物模式。凋亡膜的特征在于高水平的由半乳糖或唾液酸终止的聚糖。为了研究凝集素介导的THP-1细胞凋亡小体的吞噬作用，进行了抑制性吞噬作用测定。Galbeta1-3GalNAc或LacNAc特异性试剂（凝集素和抗体）与凋亡小体的结合消除了它们被THP-1细胞吞噬的能力，而相应的凝集素对Neu5Acalpha2-6或Neu5Acalpha2-3部位的阻断是无效的。此外，Galbeta1-3GalNAcbeta-PAA或无唾液酸GM1-PAA与THP-1细胞的结合可降低吞噬作用，而其他两种有效的THP-1结合探针 LacNAc-PAA和GalNAcbeta1-4GlcNAc-PAA不会抑制吞噬作用。因此，凋亡小体上代表的Galbeta1-3GalNAcbeta终止链而不是其他测试的半乳凝素配体似乎是THP-1细胞的靶标。