title: B cell activation leads to shedding of complement receptor type II (CR2/CD21).
abstract: Complement receptor type II (CR2/CD21) is the major receptor for C3d fragments on immune complexes. CD21 also serves as the receptor for Epstein-Barr virus in humans. On mature B cells, CD21 reduces the threshold of BCR signaling together with CD81, Leu13 and CD19, but it also occurs on other cells of the immune system where it performs unknown functions. A soluble form of CD21 (sCD21) is shed from the cell surface and is found in human blood plasma. An as-yet-unknown protease is thought to be responsible for this shedding. Altered levels of sCD21 occur in plasma in certain clinical conditions. We show here by mass spectrometry that sCD21 in human plasma of healthy donors is predominantly a short form of CD21 without the exon-11-encoded sequences. Whereas the N terminus of sCD21 was found unmodified, the C terminus is truncated, implying that only the extracellular portion of CD21 is shed. Peripheral blood B cells, but not T cells, contribute to the plasma CD21-pool. CD21 shedding is induced by stimulation with PMA plus Ca(2+) ionophore, or by stimulation of the BCR with anti-IgM+anti-CD40.
authors.affiliation: Faculty of Sciences, Department of Biology, Immunology, University of Konstanz, Konstanz, Germany.
authors.forename: Madhan
authors.initials: M
authors.lastname: Masilamani
authors.forename: Daniela
authors.initials: D
authors.lastname: Kassahn
authors.forename: Stefan
authors.initials: S
authors.lastname: Mikkat
authors.forename: Michael O
authors.initials: MO
authors.lastname: Glocker
authors.forename: Harald
authors.initials: H
authors.lastname: Illges
mesh_terms: D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D006801:Humans; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology* / Q000502:physiology; D013058:Mass Spectrometry; D008934:Mitogens / Q000494:pharmacology; D017464:Receptors, Complement 3d / Q000097:blood / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D008934:Mitogens; D017464:Receptors, Complement 3d; D013755:Tetradecanoylphorbol Acetate