IgA rheumatoid factor in mucosal fluids and serum of patients with rheumatoid arthritis: immunological aspects and clinical significance.

In order to gain insight into the production and clinical significance of IgA rheumatoid factor (IgA-RF) in mucosal fluids of patients with rheumatoid arthritis (RA), we examined tear fluid, saliva and serum from 80 patients with RA. Significant correlations were found between IgA-RF levels in tear fluid and saliva (P = 0.002, r = 0.57), saliva and serum (P < 0.001, r = 0.79), and serum and tear fluid (P < 0.001, r = 0.31). No significant correlations were found between total IgA levels in these fluids. Comparison between circulating and mucosal IgA-RF levels after correction for total IgA, revealed that mucosal IgA-RF levels are on average 2.5 times higher than circulating IgA-RF levels. Analysis of IgA-RF specificity showed that lacrimal and salivary IgA-RF reactivity with various IgG subclasses is similar and differs from serum IgA-RF specificity. These results indicate local production of IgA-RF in salivary and lacrimal glands and support the view of a common origin of IgA-RF producing B cells present in mucosal tissues. Mucosal and circulating levels of IgA and IgA-RF were not associated with tests that quantify tear fluid production. This indicates that mucosal and circulating levels of IgA and IgA-RF in patients with RA cannot be regarded as markers for the development of secondary Sjögren's syndrome.