Immunoglobulin G Subclasses of Antinuclear Antibodies and Renal Deposits. Comparison of Systemic Lupus Erythematosus, Drug‐Induced Lupus and Rheumatoid Arthritis

Immunoglobulin G (IgG) subclass representation, and titers, were studied in antinuclear antibodies (ANA) of 59 sera from patients with systemic lupus erythematosus (SLE), procainamide‐induced lupus syndrome or rheumatoid arthritis. In all the 3 groups of sera, the highest titers of ANA were found in the IgG1 subclass. Titers of this subclass were significantly higher in the SLE group, as compared with the RA group. Otherwise, no significant difference was found in the distribution of ANA among IgG subclasses in the three disorders. In a comparison of the sera of patients with SLE with and without clinical evidence of renal disease, no significant difference could be found between the titer or the distribution of ANA in the IgG subclasses. In renal tissues obtained from 8 patients, however, frequency and intensity of staining for subclasses in the glomerular deposits roughly paralleled the relative predominance of the subclasses in serum, and the titers of ANA in them. No instance of selective deposit of a single subclass was found.