Antiperinuclear factor of the IgA isotype in active rheumatoid arthritis

For rheumatoid arthritis (RA), antiperinuclear factor (APF) is as efficient a marker as rheumatoid factor (RF). However, the prevalence and significance of APF of the IgA isotype in active RA, as well as its correlation with RF-IgA, have not been determined. Our goal was to obtain information on these points.

APF-IgA were screened in 80 sera from patients with active RA, prospectively and consecutively selected over an 8-month period. Sera from 22 patients with Sjögren's syndrome and 50 with lupus were also studied retrospectively for APF-IgG and IgA.

APF-IgA were found at a 1:10 dilution or above in 31 RA sera (39%), which were all positive for APF-IgG as well at higher titers. In the 64 sera positive for APF no correlations were found between APF-IgA and IgA or immune complexes-IgA, latex, the Rose-Waaler test and RF-IgA. Conversely, an association of APF-IgA was found with both APF-IgG (p < 0.0001) and anti-stratum corneum of rat esophagus (ASC)-IgG (p < 0.0001). APF-IgA, though correlated with the presence of secondary sicca syndrome in RA (p = 0.0023), was not more frequent (5/22) in primary Sjögren's sera.

RF-IgA and APF-IgA are not correlated. Despite its localization in the mucosae, the target antigen for APF elicit fewer IgA antibodies in RA than does the RF target.