Filaggrin related antibodies among the aged

Abstract

Background: The mean age at onset of new cases of rheumatoid arthritis (RA) has increased markedly. Because the prevalence of false positive rheumatoid factor reactions increases with advancing age, the diagnostic value of this test has limitations among the aged.

Objective: To study the occurrence of two filaggrin related antibodies in an aged population.

Methods: The study covered 300 subjects aged 78-88 years, one of whom had RA. The sera were tested with enzyme linked immunosorbent assays (ELISAs), using filaggrin purified from human skin and citrullinated cyclic peptide (CCP) as antigens.

Results: One patient with RA was positive for both antibodies. When the cut off level for positive reactions was set at the 98th centile of healthy blood donors, 24 (8%) of the other subjects were positive for antibodies against filaggrin, but only one against CCP.

Conclusion: The test for anti-CCP antibody has better specificity than the test for antibodies against filaggrin among the aged.

Figure 1

Distribution of IgG class antibodies to native filaggrin purified from human skin in sera from 300 elderly subjects. The 98th centile of normal human sera is given as the cut off level for positivity.

Figure 2

Distribution of IgG class antibodies to cyclic filaggrin-derived citrullinated peptide (CCP) in sera from 300 elderly people, 33 patients with RA, and 67 normal human sera.

Figure 3

Occurrence of RF in sera from 300 elderly subjects. Cut off limits for positivity, at the 95th and 98.5th centiles of 400 normal human sera, determined in an earlier study,¹¹ are indicated.