title: CR2 units of CR2 complexes are possibly associated with nucleophilic agents through reactive covalent links.
abstract: The human complement receptor type 2 (CR2/CD21), a transmembrane glycoprotein, associates with a variety of surface antigens and proteins in the cell membrane. We examined the possibilities that the CR2 units of CR2 complexes are associated through internal covalent links reactive with nucleophilic agents, e.g. H(2)O or methylamine, and that CR2-positive cells process anti-CR2 monoclonal antibodies (MoAbs). Data from immunoblotting and cytofluorimetry with CR2-binding site-specific MoAbs show that: (i) CR2-positive Raji cells release soluble CR2 isoforms into the medium when incubated in phosphate buffered saline; (ii) despite affecting the detection of one soluble CR2 isoform, methylamine treatment of soluble CR2 allows the detection of another of its isoforms; (iii) limited pre-treatment of cells with methylamine reveals a more heterogeneous CR2-positive cell population or enhances the detection of CR2; (iv) cell treatment with CR2-binding site-specific MoAbs enhances the detection of CR2 isoform(s). The data suggest that CR2 is shed mainly as a soluble CR2 complex, in which the CR2 units link covalently and react with nucleophilic agents. Raji cells may process bound fragments (145 kDa) that are recognised by and become bound by anti-CR2 MoAb.
authors.affiliation: Istituto Tecnologie Biomediche, CNR, V.le Marx 43, 00137 Rome, Italy.
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Di Certo
authors.forename: Alberto
authors.initials: A
authors.lastname: Faggioni
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Barile
mesh_terms: D000911:Antibodies, Monoclonal / Q000378:metabolism / Q000494:pharmacology; D001665:Binding Sites / Q000187:drug effects / Q000276:immunology; D002460:Cell Line; D003176:Complement C3 / Q000378:metabolism / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D005434:Flow Cytometry; D006801:Humans; D015151:Immunoblotting; D007074:Immunoglobulin G / Q000378:metabolism / Q000494:pharmacology; D008744:Methylamines / Q000494:pharmacology; D011233:Precipitin Tests; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D017464:Receptors, Complement 3d / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*; D012995:Solubility
chemical_list: D000911:Antibodies, Monoclonal; D003176:Complement C3; D007074:Immunoglobulin G; D008744:Methylamines; D011500:Protein Synthesis Inhibitors; D017464:Receptors, Complement 3d; D003513:Cycloheximide; C027451:methylamine