To investigate the occurrence of IgA autoantibodies to Ro 52 kDa, Ro 60 kDa and La antigen in serum of patients with primary Sjögren's syndrome (pSS) and systemic lupus erythematosus (SLE).
Recombinant Ro 52 kDa, Ro 60 kDa and La antigens were used to analyse autoantibodies in serum from 25 patients with pSS, 30 patients with SLE and 20 controls using a semiquantitative immunoblotting approach.
Among the patients with pSS, 21 (84%) had detectable IgA autoantibodies to Ro 52 kDa, 13 (52%) to Ro 60 kDa and 20 (80%) to La antigen. The corresponding results for the patients with SLE were 22 (73%), 14 (47%) and 20 (67%), respectively. No IgA autoantibodies against the three antigens were detected in 20 normal controls. A comparison of several clinical features with the titres of IgA antibodies to Ro 52 kDa, Ro 60 kDa and La, revealed a significant relation between IgA anti-Ro 52 and IgA anti-La to sicca (p< 0.05). Semiquantitative data suggest that IgG is the dominating antibody to the three antigens followed by IgM > IgA in both SLE and pSS patients. Specificity studies of IgA autoantibodies with different subfragments of Ro 52 kDa and Ro 60 kDa antigens showed that IgA antibodies did not differ from IgG and IgM in their recognition pattern.
These results suggest that besides IgM and IgG, IgA autoantibodies are also detected at high frequency in patients with pSS and SLE. Further studies are necessary to evaluate the contribution of these IgA autoantibodies to inflammation as well as their diagnostic value.