Probing the cis interactions of the inhibitory receptor Siglec-7 with alpha2,8-disialylated ligands on natural killer cells and other leukocytes using glycan-specific antibodies and by analysis of alpha2,8-sialyltransferase gene expression

J Leukoc Biol. 2006 Oct;80(4):787-96. doi: 10.1189/jlb.1005559. Epub 2006 Jul 20.


Siglec-7 is a CD33-related sialic acid-binding Ig-like lectin expressed strongly on NK cells, where it can function as an inhibitory receptor. Its sialic acid-binding activity on NK cells is masked by cis interactions with sialylated glycans, which are likely to be important for regulating the inhibitory function of Siglec-7, which exhibits an unusual preference for alpha2,8-linked disialic acids, a motif found in "b-series" gangliosides and some glycoproteins. To investigate the presence of alpha2,8-linked disialic acids on NK cells, T cells, monocytes, and B cells, we first analyzed their expression of all known alpha2,8-sialyltransferase genes by quantitative PCR. Unlike T cells, B cells, and monocytes, NK cells consistently expressed mRNA encoding ST8Sia VI, which creates alpha2,8-linked disialic acids on O-linked glycans of glycoproteins. All blood leukocytes expressed ST8Sia IV, implicated in polysialic acid synthesis, and NK cells variably expressed high levels of ST8Sia V mRNA required for GT3 expression. Two human IgM antibodies, Ha1 and Pi1, with specificity for the alpha2,8-disialyl motif reacted strongly with NK cells in a sialic acid-dependent manner and less strongly with T cells and monocytes. Antibody-induced clustering of Siglec-7 on NK cells resulted in partial colocalization with anti-Ha1. Finally, MALDI-TOF mass spectrometric analysis of isolated NK cell O-glycans revealed the presence of a peak at mass-to-charge ratio of 1619.4 mass units, corresponding to a putative alpha2,8-disialylated glycan. Together, these results suggest that NK cells are decorated with alpha2,8-disialic acid structures implicated in regulation of cellular activation via interactions with Siglec-7.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal / chemistry
  • Antibodies, Monoclonal / immunology*
  • Antigens, Differentiation, Myelomonocytic / immunology*
  • Antigens, Differentiation, Myelomonocytic / metabolism
  • Cell Line, Tumor
  • Gene Expression Profiling
  • Humans
  • Killer Cells, Natural / immunology*
  • Lectins / immunology*
  • Lectins / metabolism
  • Leukocytes / immunology*
  • Leukocytes, Mononuclear / enzymology
  • Leukocytes, Mononuclear / immunology
  • Ligands
  • Mice
  • Polysaccharides / chemistry
  • Polysaccharides / immunology
  • RNA, Messenger / genetics
  • Reverse Transcriptase Polymerase Chain Reaction / methods
  • Sensitivity and Specificity
  • Sialic Acids / chemistry
  • Sialic Acids / metabolism*
  • Sialyltransferases / biosynthesis
  • Sialyltransferases / genetics*
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / methods
  • Stereoisomerism
  • Structure-Activity Relationship


  • Antibodies, Monoclonal
  • Antigens, Differentiation, Myelomonocytic
  • Lectins
  • Ligands
  • Polysaccharides
  • RNA, Messenger
  • SIGLEC7 protein, human
  • Sialic Acids
  • Sialyltransferases
  • alpha2,8-sialyltransferase VI