IgG subclasses of anti-SS-A/Ro in patients with primary Sjögren's syndrome.

Patients with primary Sjögren's syndrome mostly have high levels of polyclonal IgG, and subclass analysis frequently shows selective IgG1 increase with low IgG2. In this study IgG subclass profiles of anti-SS-A/Ro were examined using ELISA technique. Results show marked IgG subclass restriction of anti-SS-A/Ro autoantibodies (high IgG1/low IgG2). Comparison of the levels of specific IgG subclass autoantibodies with total levels of the corresponding subclass disclosed divergence regarding IgG2, IgG3, and IgG4, but not IgG1. Thus, total levels of IgG1 paralleled the levels of IgG1 anti-SS-A antibodies. Specific autoantibodies of IgG2 subclass could not be detected despite low or normal levels of total IgG2. Elevated levels of specific IgG3 and IgG4 antibodies were seen, although total levels of the corresponding subclasses were within normal limits. These findings may possibly be of relevance with regard to antigen-driven activation of autoantibody-producing plasma cell clones.