title: IgG Subclass Specificity Discriminates Restricted IgM Rheumatoid Factor Responses From More Mature Anti-Citrullinated Protein Antibody-Associated or Isotype-Switched IgA Responses.
abstract: OBJECTIVE
  To investigate the presence and patterns of specific IgG subclass recognition by IgM rheumatoid factor (IgM-RF) and IgA-RF with a newly developed enzyme-linked immunosorbent assay (ELISA), which can discriminate between polyspecific and restricted RF responses.
  
  
  METHODS
  Polyspecific and restricted RF responses were determined with our ELISA, which uses individually coated recombinant IgG subclasses instead of polyclonal IgG as target antibodies. Fine specificity was determined using target antibodies with single amino acid mutations in the Fc region.
  
  
  RESULTS
  In a screening panel of 93 sera that were previously found to be IgM-RF positive in a conventional RF assay, we were able to discriminate between sera with polyspecific IgM-RF responses (i.e., RF responses directed against all 4 IgG subclasses) and those with restricted IgM-RF responses, with low or absent relative reactivity against IgG2, IgG3, or IgG4. We found the largest variation for anti-IgG3 reactivity. Samples without detectable anti-IgG4 reactivity formed an independent group from the other restricted RF responses and the polyspecific RF responses. The specificity of these anti-IgG4-negative sera could be pinpointed to single amino acid differences between IgG1 and IgG4. Polyspecific RF responses more often showed signs of RF response maturation, with more isotype switching to IgA-RF, as compared to restricted RF responses. In a cohort of IgM-RF+ and/or anti-citrullinated protein antibody (ACPA)-positive arthralgia patients, we found restricted RF responses in 35% (49 of 140) of RF+/ACPA- patients, while RF+/ACPA+ patients, who have a much higher risk of developing rheumatoid arthritis, virtually always (123 of 128 [96%]) showed a polyspecific RF response.
  
  
  CONCLUSIONS
  IgG subclass-specific RF distinguishes between immature restricted RF responses and potentially more pathogenic, ACPA-associated polyspecific responses.
authors.affiliation: Amsterdam Rheumatology and immunology Center, Reade, and Sanquin Research, Amsterdam, The Netherlands.
authors.forename: Willem J J
authors.initials: WJ
authors.lastname: Falkenburg
authors.affiliation: Amsterdam Rheumatology and immunology Center, Reade, and Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Dirkjan
authors.initials: D
authors.lastname: van Schaardenburg
authors.affiliation: Sanquin Research, and Landsteiner Laboratory, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Pleuni
authors.initials: P
authors.lastname: Ooijevaar-de Heer
authors.affiliation: Amsterdam Rheumatology and immunology Center, and Reade, Amsterdam, The Netherlands.
authors.forename: Gertjan
authors.initials: G
authors.lastname: Wolbink
authors.affiliation: Sanquin Research, and Landsteiner Laboratory, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Theo
authors.initials: T
authors.lastname: Rispens
mesh_terms: D000918:Antibody Specificity / Q000276:immunology*; D001172:Arthritis, Rheumatoid / Q000276:immunology*; D001323:Autoantibodies / Q000276:immunology; D016022:Case-Control Studies; D015331:Cohort Studies; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007070:Immunoglobulin A / Q000276:immunology*; D017578:Immunoglobulin Class Switching; D007074:Immunoglobulin G / Q000145:classification / Q000276:immunology*; D007075:Immunoglobulin M / Q000276:immunology*; D010456:Peptides, Cyclic / Q000276:immunology; D012217:Rheumatoid Factor / Q000276:immunology*
chemical_list: D001323:Autoantibodies; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide; D012217:Rheumatoid Factor