title: Reactivity of human IgM binding murine monoclonal 6B6C1 (IgG2a) with other murine monoclonal IgG antibodies.
abstract: BACKGROUND
  Approximately 6% of sera positive in a dengue virus IgM-capture enzyme immunoassay (EIA) represent false-positives due to interaction between IgM and horseradish peroxidase (HRP)-labeled monoclonal antibody (MAb) 6B6C1 (IgG2a). To better understand this interaction, we assessed the reactivity of captured IgM from these sera with other HRP-labeled MAbs.
  
  
  METHODS
  Fifty dengue IgM false-positive sera (recognizing 6B6C1) were evaluated for IgM reactivity with the HRP-labeled MAbs H3A4 (IgG2a), 53.8 (IgG2b), and IL-A2 (IgG1). The sera were also tested in an EIA for human anti-mouse antibody (HAMA).
  
  
  RESULTS
  Forty-three sera (86%) reacted with IgG2a MAb (H3A4). Most (31/43 = 72%) of these sera recognizing 6B6C1 and H3A4 also recognized the IgG2 MAb and/or the IgG1 MAb. In contrast, HAMA was increased in only 9 of 50 (18%) sera reacting with 6B6C1.
  
  
  CONCLUSIONS
  IgM from most sera-binding IgG2a MAb 6B6C1 also binds another IgG2a MAb, suggesting that IgM-6B6C1 reactivity is not idiotype specific. In many cases, IgM recognizing 6B6C1 also binds MAbs of other IgG subclasses, but is negative in a HAMA assay. These findings indicate that samples positive in IgM-capture EIAs utilizing conjugated MAbs should always be retested in the absence of antigen to identify false-positive reactivity caused by direct IgM-MAb interaction.
authors.affiliation: Focus Diagnostics, Inc., Cypress, CA 90630, USA. hprince@focusdx.com
authors.forename: Harry E
authors.initials: HE
authors.lastname: Prince
authors.forename: Cindy
authors.initials: C
authors.lastname: Yeh
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000378:metabolism; D000918:Antibody Specificity; D003715:Dengue / Q000097:blood / Q000175:diagnosis / Q000276:immunology; D005189:False Positive Reactions; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods* / Q000592:standards; D007074:Immunoglobulin G / Q000737:chemistry* / Q000378:metabolism; D007075:Immunoglobulin M / Q000097:blood / Q000737:chemistry* / Q000378:metabolism; D051379:Mice; D011485:Protein Binding
chemical_list: D000911:Antibodies, Monoclonal; D007074:Immunoglobulin G; D007075:Immunoglobulin M