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New markers and an old phenomenon: prozone effect disturbing detection of filaggrin (keratin) autoantibodies
  1. Frederique Dubois-Galopin1,
  2. Celine Beauvillain1,
  3. Damien Dubois1,
  4. Anne Pillet1,
  5. Gilles Renier1,
  6. Pascale Jeannin1,
  7. Charles Masson2,
  8. Alain Chevailler1
  1. 1Immunology and Allergology Laboratory, CHU Angers, France
  2. 2Rheumatology, CHU Angers, France
  1. Correspondence to:
    A Chevailler
    Laboratoire d’Immunologie et d’Allergologie, Hôpital Larrey, CHU 49933 Angers cedex 9, France; alchevailler{at}

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Anti-filaggrin antibodies, also named anti-keratin antibodies (AKA), are serum IgG labelling the stratum corneum of the rat oesophagus epithelium, detectable by indirect immunofluorescence (IIF). They constitute a specific marker for the diagnosis of rheumatoid arthritis (RA).1–3

A laminar staining pattern is seen with most AKA-positive sera (fig 1A), but occasionally the cornified layer is diffusely labelled, and the image also shows foamy staining (fig 1B). Although most authors consider sera as AKA positive only when a linear laminated pattern is observed,4,5 some consider the sera as AKA positive even when the staining is diffuse or foamy.6

Figure 1

 Anti-keratin antibodies (AKA) detected by indirect immunofluorescence on rat oesophagus. (A) Typical linear laminated labelling pattern restricted to the upper cornified layer observed in the serum …

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  • Competing interests: None declared.