Abstract
BackgroundSiglec-7, a sialic acid binding inhibitory receptor expressed by NK cells is masked in vivo by a so far unknown ligand. It shows a strong binding prevalence for α-2,8-linked disialic acids in vitro.ResultsHere we describe the expression of PSA-NCAM (α-2,8-linked polysialic acid modified NCAM) on functional adult peripheral blood natural killer cells and examine its possible role in masking Siglec-7. Unmasking of Siglec-7 using Clostridium perfringens neuraminidase massively reduces NK cell cytotoxicity. By contrast a specific removal of PSA using Endo-NF does not lead to a reduction of NK cell cytotoxicity.ConclusionThe results presented here therefore indicate that PSA-NCAM is not involved in masking Siglec-7.
Highlights
Siglec-7, a sialic acid binding inhibitory receptor expressed by NK cells is masked in vivo by a so far unknown ligand
NCAM is an immunoglobulin-like cell adhesion molecule (IgCAM) and was the first vertebrate protein demonstrated to be glycosylated with polysialic acid (PSA), which is a homomeric polymer of α-2,8-sialic acid
Co-expression of PSA and CD56 was verified by immunocytochemical staining (Fig. 1B)
Summary
Siglec-7, a sialic acid binding inhibitory receptor expressed by NK cells is masked in vivo by a so far unknown ligand. It shows a strong binding prevalence for α-2,8-linked disialic acids in vitro. Siglec-7 (p75/AIRM1) is a sialic acid binding inhibitory receptor expressed on NK and NKT cells and to a lesser extend on monocytes [1]. It shows a prevalence for binding α-2,8-linked or branched α-2,6-linked sialic acids in vitro and is constitutively masked by a endogenous ligand in vivo [2] which has not been identified yet. Until now only very few proteins have been reported to be modified with PSA [4,5]
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