title: CD22 serves as a receptor for soluble IgM.
abstract: CD22 (Siglec-2) is a B-cell membrane-bound lectin that recognizes glycan ligands containing α2,6-linked sialic acid (α2,6Sia) and negatively regulates signaling through the B-cell Ag receptor (BCR). Although CD22 has been investigated extensively, its precise function remains unclear due to acting multiple phases. Here, we demonstrate that CD22 is efficiently activated in trans by complexes of Ag and soluble IgM (sIgM) due to the presence of glycan ligands on sIgM. This result strongly suggests sIgM as a natural trans ligand for CD22. Also, CD22 appears to serve as a receptor for sIgM, which induces a negative feedback loop for B-cell activation similar to the Fc receptor for IgG (FcγRIIB).
authors.affiliation: Department of Immunology, Medical Research Institute, Tokyo Medical and Dental University, Bunkyo-ku, Tokyo, Japan. tadachi.imm@mri.tmd.ac.jp
authors.forename: Takahiro
authors.initials: T
authors.lastname: Adachi
authors.forename: Satoru
authors.initials: S
authors.lastname: Harumiya
authors.forename: Hiromu
authors.initials: H
authors.lastname: Takematsu
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Kozutsumi
authors.forename: Matthias
authors.initials: M
authors.lastname: Wabl
authors.forename: Manabu
authors.initials: M
authors.lastname: Fujimoto
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Tedder
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D015153:Blotting, Western; D045744:Cell Line, Tumor; D005246:Feedback; D005434:Flow Cytometry; D007075:Immunoglobulin M / Q000276:immunology* / Q000378:metabolism; D008024:Ligands; D051379:Mice; D018345:Mice, Knockout; D011947:Receptors, Antigen, B-Cell / Q000276:immunology* / Q000378:metabolism; D051918:Sialic Acid Binding Ig-like Lectin 2 / Q000276:immunology* / Q000378:metabolism
chemical_list: D007075:Immunoglobulin M; D008024:Ligands; D011947:Receptors, Antigen, B-Cell; D051918:Sialic Acid Binding Ig-like Lectin 2