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Arthritis Rheum. 2010 Nov;62(11):3345-52. doi: 10.1002/art.27644.

Anticitrulline antibodies can be caused by homocitrulline-containing proteins in rabbits.

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1
University of Oulu, Oulu, Finland.

Abstract

OBJECTIVE:

To clarify the possible roles of protein-bound homocitrulline in causing an antibody response to citrulline and as a confounding factor in citrulline detection assays.

METHODS:

Native, carbamoylated, and citrullinated albumins were used for testing the specificity of commercial antibodies against modified citrulline by Western blot. Rabbits were immunized with human albumin and/or bone type I collagen, both of which were treated with cyanate to produce homocitrulline, or with citrullinated synthetic telopeptide of type I collagen. These antisera were tested for binding to cyclic citrullinated peptide 2 (CCP-2), mutated citrullinated vimentin, and type I or II collagen telopeptides containing either citrulline or homocitrulline.

RESULTS:

Commercial antibodies that had been considered to be specific for chemically modified citrulline were found to recognize both homocitrulline- and citrulline-containing albumins. The rabbits immunized with proteins containing homocitrulline produced high-affinity antibodies against CCP-2 and, to a lesser extent, against mutated citrullinated vimentin. The antisera also bound homocitrulline-containing collagen telopeptides and, less strongly, citrulline-containing telopeptides.

CONCLUSION:

Our findings demonstrate that homocitrulline, which is a structural analog of citrulline (longer by 1 carbon, and readily formed in the body), can be involved in raising citrulline-recognizing antibodies in experimental animals and can cause false-positive reactions in assays for citrulline.

PMID:
20617522
DOI:
10.1002/art.27644
[Indexed for MEDLINE]
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