title: Complement receptor type 1 (CR1, CD35) is a potent inhibitor of B-cell functions in rheumatoid arthritis patients.
abstract: The involvement of B cells, complement activation and subsequent immune complex deposition has all been implicated in the pathogenesis of rheumatoid arthritis (RA). Although the reduced expression of complement receptor 1 (CR1, CD35) and 2 (CR2, CD21) on the B cells of RA patients has been known for a long time, their exact role in B-cell tolerance and autoimmunity is not yet fully understood. To get a deeper insight into the possible mechanisms, we studied the expression and function of CR1 and CR2 on various subsets of B cells of healthy donors and RA patients at various stages of the disease by FACS analysis, (3)H-thymidine incorporation and ELISA. We found that CD19(+)CD27(-) naive B cells up-regulate the expression of the inhibitory CR1 during differentiation to CD19(+)CD27(+) memory B cells both in healthy donors and in RA patients, whereas the expression of the activatory CR2 is down-regulated. This clearly demonstrates that the expression of these two antagonistic complement receptors is regulated differentially during the development of human B cells, a phenomenon which may influence the maintenance of peripheral B-cell tolerance. Our functional studies show that after clustering CR1 both by its natural ligand and To5 mAb, the inhibitory function of CD35 is maintained in RA patients, despite its significantly reduced expression compared with healthy individuals. Besides blocking B-cell receptor-induced proliferation, CR1 inhibits the differentiation of B cells to plasmablasts and their immunoglobulin production. Since the reduced expression of CR1 in RA patients does not affect its inhibitory function, this receptor might serve as a new target for therapeutical interventions.
authors.affiliation: Department of Immunology, Eötvös Loránd University, Pázmány Péter s. 1/C,  Budapest H-1117, Hungary.
authors.forename: Mariann
authors.initials: M
authors.lastname: Kremlitzka
authors.forename: Anna
authors.initials: A
authors.lastname: Polgár
authors.forename: Lívia
authors.initials: L
authors.lastname: Fülöp
authors.forename: Emese
authors.initials: E
authors.lastname: Kiss
authors.forename: Gyula
authors.initials: G
authors.lastname: Poór
authors.forename: Anna
authors.initials: A
authors.lastname: Erdei
mesh_terms: D000328:Adult; D000368:Aged; D018941:Antigens, CD19 / Q000235:genetics / Q000276:immunology; D001172:Arthritis, Rheumatoid / Q000276:immunology* / Q000473:pathology; D015551:Autoimmunity; D001402:B-Lymphocytes / Q000276:immunology* / Q000473:pathology; D016022:Case-Control Studies; D002454:Cell Differentiation; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000276:immunology; D006801:Humans; D056724:Immunity, Humoral; D007156:Immunologic Memory; D008297:Male; D008875:Middle Aged; D061166:Peripheral Tolerance; D011947:Receptors, Antigen, B-Cell / Q000235:genetics / Q000276:immunology; D017463:Receptors, Complement 3b / Q000235:genetics / Q000276:immunology*; D017464:Receptors, Complement 3d / Q000235:genetics / Q000276:immunology*; D015398:Signal Transduction; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7 / Q000235:genetics / Q000276:immunology
chemical_list: D018941:Antigens, CD19; C509991:CR1 protein, human; D011947:Receptors, Antigen, B-Cell; D017463:Receptors, Complement 3b; D017464:Receptors, Complement 3d; D018127:Tumor Necrosis Factor Receptor Superfamily, Member 7