Mediates B-cell B-cell interactions. May be involved in the localization of B-cells in lymphoid tissues. Binds sialylated glycoproteins, one of which is CD45. Preferentially binds to alpha-2,6-linked sialic acid. The sialic acid recognition site can be masked by cis interactions with sialic acids on the same cell surface. Upon ligand induced tyrosine phosphorylation in the immune response seems to be involved in regulation of B-cell antigen receptor signaling. Plays a role in positive regulation through interaction with Src family tyrosine kinases and may also act as an inhibitory receptor by recruiting cytoplasmic phosphatases via their SH2 domains that block signal transduction through dephosphorylation of signaling molecules.
CD33 is a type I Lectin belonging to the Ig superfamily. CD33 contains an N terminal Ig like V type domain, which mediates sialic acid binding, followed by one Ig like C2 type domain, a transmembrane region and a cytoplasmic tail containing two conserved immunoreceptor tyrosine based inhibition motifs (ITIMs). Eleven human Siglecs have been characterized. Siglecs 5 to 11 share a high degree of sequence similarity with CD33/Siglec3 both in their extracellular and intracellular regions. They are collectively referred to as CD33 related Siglecs. CD33 related Siglecs have differential expression pattern within the hematopoietic system. They are involved in the regulation of cellular activation within the immune system. Siglec 3 expression is restricted to cells of myelomonocytic lineage. Siglec3 recruits SHP1 and SHP2 to its ITIMs upon phosphorylation.
Myeloid cell surface antigen CD33 also known as Sialic acid binding Ig-like lectin 3, CD33 antigen or Siglec-3, is a member of the immunoglobulin superfamily and SIGLEC (sialic acid binding Ig-like lectin) family. This Single-pass type I membrane protein contains 1 Ig-like C2-type (immunoglobulin-like) domain and 1 Ig-like V-type (immunoglobulin-like) domain. CD33 /Siglec-3 is a putative adhesion molecule of myelomonocytic-derived cells that mediates sialic-acid dependent binding to cells. CD33 /Siglec-3 preferentially binds to alpha-2,6-linked sialic acid. The sialic acid recognition site may be masked by cis interactions with sialic acids on the same cell surface. In the immune response, may act as an inhibitory receptor upon ligand induced tyrosine phosphorylation by recruiting cytoplasmic phosphatase(s) via their SH2 domain(s) that block signal transduction through dephosphorylation of signaling molecules. CD33/Siglec-3 induces apoptosis in acute myeloid leukemia (in vitro). CD33/Siglec-3 can function as a sialic acid-dependent cell adhesion molecule and that binding can be modulated by endogenous sialoglycoconjugates when CD33 is expressed in a plasma membrane.
SIGLEC5 contains 2 Ig-like C2-type (immunoglobulin-like) domains and 1 Ig-like V-type (immunoglobulin-like) domain. It belongs to the immunoglobulin superfamily and SIGLEC (sialic acid binding Ig-like lectin) family. SIGLEC5 is expressed by monocytic/myeloid lineage cells. It is found at high levels in peripheral blood leukocytes; spleen; bone marrow and at lower levels in lymph node; lung; appendix; placenta; pancreas and thymus. It is also expressed by monocytes and neutrophils but absent from leukemic cell lines representing early stages of myelomonocytic differentiation. SIGLEC5 is a putative adhesion molecule that mediates sialic-acid dependent binding to cells. It binds equally to alpha-2;3-linked and alpha-2;6-linked sialic acid. The sialic acid recognition site may be masked by cis interactions with sialic acids on the same cell surface.
Human Siglec-5 are Itype(Igtype) lectins belonging to the Ig superfamily;They are characterized by an N terminal Ig-like V type domain which mediates sialic acid binding; followed by varying numbers of Ig-like C2 type domains. SIGLEC5 has also been designated CD170; they are expressed by monocytic or myeloid lineage cells; and also found at high levels in peripheral blood leukocytes; spleen; bone marrow and at lower levels in lymph node; lung; appendix; placenta; pancreas and thymus. SIGLEC5 are expressed by monocytes and neutrophils but absent from leukemic cell lines representing early stages of myelomonocytic differentiation. Siglec5 to 11 share a high degree of sequence similarity with CD33/Siglec3 both in their extracellular and intracellular regions. They are collectively referred to as CD33 related Siglecs. One remarkable feature of the CD33 related Siglecs is their differential expression pattern within the hematopoietic system This fact; together with the presence of two conserved immunoreceptor tyrosinebased inhibition motifs (ITIMs) in their cytoplasma tails; suggests that CD33 related Siglecs are involved in the regulation of cellular activation within the immune system.
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