title: B cell depletion with rituximab in patients with rheumatoid arthritis: Multiplex bead array reveals the kinetics of IgG and IgA antibodies to citrullinated antigens.
abstract: The serology of patients with Rheumatoid arthritis (RA) is characterized by persistently raised levels of autoantibodies: Rheumatoid Factors (RhF) against Fc of IgG, and to citrullinated (Cit) protein/peptide sequences: ACPA, recognizing multiple Cit-sequences. B cell depletion therapy based on rituximab delivers good clinical responses in RA patients, particularly in the seropositive group, with responses sometimes lasting beyond the phase of B cell reconstitution. In general, ACPA levels fall following rituximab, but fluctuations with respect to predicting relapse have proved disappointing. In order to identify possible immunodominant specificities within either IgG- or IgA-ACPA we used a Multiplex bead-based array consisting of 30 Cit-peptides/proteins and 22 corresponding native sequences. The kinetics of the serum ACPA response to individual specificities was measured at key points (Baseline, B cell depletion phase, Relapse) within an initial cycle of rituximab therapy in 16 consecutive patients with severe, active RA. All had achieved significant decreases in Disease Activity Scores-28 and maintained B cell depletion in the peripheral blood (<5 CD19+cells/μl) for at least 3 months. At Baseline, mean fluorescence intensity shown by individual IgG- and IgA-ACPA were strongly correlated (R(2) = 0.75; p < 0.0001) but IgA-ACPA were approximately 10-fold lower. Data were Z-normalised in order to compare serial results and antibody classes. At Baseline, a total of 68 IgG- and 51 IgA-ACPA had Z-scores ≥ 1 (above population mean) were identified, with at least one Cit-antigen identified in each serum. ACPA to individual specificities subsequently fluctuated with 3 different patterns. Most 51/68 (75%) IgG- and 48/51 IgA-ACPA (94%) fell between Baseline and Depletion, of which 57% IgG- and 65% IgA-ACPA rebounded pre-Relapse. Interestingly, 17/68 IgG-ACPA (25%) and some IgA-ACPA (3/51; 6%) transiently increased from Baseline, subsequently falling pre-Relapse. Individual responses to particular Cit-epitopes were not linked to particular patterns of fluctuation, but IgG- and IgA-ACPA to individual Cit-antigens often followed similar courses. Some new IgG- and IgA-ACPA, generally to different Cit-antigens however, arose at Relapse in 4 patients. The complexities of the ACPA response after rituximab may therefore reflect its ability to deplete or modify the function of parent B cell clones, which varies between patients. Although relapse following rituximab invariably follows naïve B cell exit from the bone marrow, these studies show that interactions between both 'new' and residual autoreactive memory B cells may be key to resumption of symptoms. The lack of identification of any immunodominant specificity suggests that the process of citrullination, rather than any particular Cit-antigen drives the autoimmune response in RA patients.
authors.affiliation: Department of Rheumatology, University College London, UK. Electronic address: g.cambridge@ucl.ac.uk.
authors.forename: Geraldine
authors.initials: G
authors.lastname: Cambridge
authors.affiliation: Department of Rheumatology, University College London, UK.
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Leandro
authors.affiliation: VA Palo Alto Healthcare System and Stanford University, USA.
authors.forename: Lauren J
authors.initials: LJ
authors.lastname: Lahey
authors.affiliation: Department of Rheumatology, University College London, UK.
authors.forename: Thomas
authors.initials: T
authors.lastname: Fairhead
authors.affiliation: VA Palo Alto Healthcare System and Stanford University, USA.
authors.forename: William H
authors.initials: WH
authors.lastname: Robinson
authors.affiliation: VA Palo Alto Healthcare System and Stanford University, USA.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Sokolove
mesh_terms: D000328:Adult; D000368:Aged; D018501:Antirheumatic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D001172:Arthritis, Rheumatoid / Q000188:drug therapy* / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood / Q000276:immunology; D001324:Autoantigens / Q000276:immunology; D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D016000:Cluster Analysis; D004359:Drug Therapy, Combination; D018604:Epitope Mapping; D000939:Epitopes / Q000276:immunology; D005260:Female; D006801:Humans; D007070:Immunoglobulin A / Q000097:blood / Q000276:immunology; D007074:Immunoglobulin G / Q000097:blood / Q000276:immunology; D008212:Lymphocyte Depletion / Q000379:methods; D008297:Male; D008875:Middle Aged; D010446:Peptide Fragments / Q000276:immunology; D012217:Rheumatoid Factor; D000069283:Rituximab / Q000494:pharmacology / Q000627:therapeutic use*; D016896:Treatment Outcome
chemical_list: D018501:Antirheumatic Agents; D001323:Autoantibodies; D001324:Autoantigens; D000939:Epitopes; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D010446:Peptide Fragments; D000069283:Rituximab; D012217:Rheumatoid Factor
keywords: Autoantibodies; Citrullination; Rheumatoid arthritis; Rituximab