Immunoglobulin G subclass distribution of autoantibodies in systemic sclerosis, primary biliary cirrhosis, and overlap syndromes.

The IgG subclass reactivities of six anticellular antibodies were measured by indirect immunofluorescence on HEp2 cells using murine monoclonal antibodies to the four human IgG subclasses. Patients with scleroderma, primary biliary cirrhosis (PBC), systemic lupus erythematosus, and mixed connective tissue disease were studied. Anticentromere antibody (ACA) was virtually all IgG1 and 3; antibody to multiple nuclear dots (NSpI) was IgG1, 2, and 3; antimitochondrial antibody was mainly IgG2 and 3; nucleolar staining was varied in subclass reactivity but most often IgG4; the diffusely grainy staining associated with Scl-70 antibody was chiefly IgG1; and the speckled pattern associated with anti-RNP antibody was always IgG1 and 4, with IgG2 and 3 in some cases. These data fail to support the hypothesis that the various patterns of autoimmune disease reflect differences in the biological properties of the associated antibodies. The prominence of IgG2 in antibodies associated with PBC suggests the possibility of an immune response independent of T cells in that condition. Differential subclass staining showed an unexpectedly high frequency of antibody to multiple nuclear dots in ACA positive sera, and such patients (all with CREST syndrome) could be at increased risk of developing PBC later.