Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan.
PLoS One. 2013 Jun 6;8(6):e65070. doi: 10.1371/journal.pone.0065070. Print 2013.
CLEC4F, a member of C-type lectin, was first purified from rat liver extract with high binding affinity to fucose, galactose (Gal), N-acetylgalactosamine (GalNAc), and un-sialylated glucosphingolipids with GalNAc or Gal terminus. However, the biological functions of CLEC4F have not been elucidated. To address this question, we examined the expression and distribution of murine CLEC4F, determined its binding specificity by glycan array, and investigated its function using CLEC4F knockout (Clec4f-/-) mice. We found that CLEC4F is a heavily glycosylated membrane protein co-expressed with F4/80 on Kupffer cells. In contrast to F4/80, CLEC4F is detectable in fetal livers at embryonic day 11.5 (E11.5) but not in yolk sac, suggesting the expression of CLEC4F is induced as cells migrate from yolk cells to the liver. Even though CLEC4F is not detectable in tissues outside liver, both residential Kupffer cells and infiltrating mononuclear cells surrounding liver abscesses are CLEC4F-positive upon Listeria monocytogenes (L. monocytogenes) infection. While CLEC4F has strong binding to Gal and GalNAc, terminal fucosylation inhibits CLEC4F recognition to several glycans such as Fucosyl GM1, Globo H, Bb3∼4 and other fucosyl-glycans. Moreover, CLEC4F interacts with alpha-galactosylceramide (α-GalCer) in a calcium-dependent manner and participates in the presentation of α-GalCer to natural killer T (NKT) cells. This suggests that CLEC4F is a C-type lectin with diverse binding specificity expressed on residential Kupffer cells and infiltrating monocytes in the liver, and may play an important role to modulate glycolipids presentation on Kupffer cells.
C 型凝集素成员 CLEC4F 最初从大鼠肝提取物中纯化出来，对岩藻糖、半乳糖（Gal）、N-乙酰半乳糖胺（GalNAc）以及具有 GalNAc 或 Gal 末端的未唾液酸化糖鞘脂具有高结合亲和力。然而，CLEC4F 的生物学功能尚未阐明。为了解决这个问题，我们检查了小鼠 CLEC4F 的表达和分布，通过聚糖阵列确定了其结合特异性，并使用 CLEC4F 敲除（Clec4f-/-）小鼠研究了其功能。我们发现 CLEC4F 是一种高度糖基化的膜蛋白，与 Kupffer 细胞上的 F4/80 共表达。与 F4/80 不同，CLEC4F 可在胚胎第 11.5 天（E11.5）的胎肝中检测到，但在卵黄囊中不可检测，这表明 CLEC4F 的表达是在细胞从卵黄细胞迁移到肝脏时诱导的。尽管 CLEC4F 在肝脏以外的组织中不可检测，但在李斯特菌（Listeria monocytogenes，L. monocytogenes）感染时，常驻 Kupffer 细胞和浸润肝脓肿周围的单核细胞均为 CLEC4F 阳性。虽然 CLEC4F 与 Gal 和 GalNAc 具有强烈的结合能力，但末端岩藻糖基化抑制了 CLEC4F 对几种糖的识别，如 Fucosyl GM1、Globo H、Bb3∼4 和其他岩藻糖聚糖。此外，CLEC4F 以钙离子依赖的方式与α-半乳糖神经酰胺（α-GalCer）相互作用，并参与将α-GalCer 呈递给自然杀伤 T（NKT）细胞。这表明 CLEC4F 是一种具有多种结合特异性的 C 型凝集素，表达于肝脏中的常驻 Kupffer 细胞和浸润的单核细胞上，可能在调节 Kupffer 细胞上糖脂的呈递方面发挥重要作用。
