Distribution of IgG subclasses among human autoantibodies to Sm, RNP, dsDNA, SS-B and IgG rheumatoid factor

The IgG subclass distribution of human autoantibodies to Sm, double-stranded DNA (ds-DNA), ribonucleoprotein (RNP), SS-B (La), and IgG rheumatoid factor (RF) have been determined using sensitive ELISA or by indirect immunofluorescence on Crithidia lucilia in sera from patients with systemic lupus erythematosus (SLE), Sjögren's syndrome, and rheumatoid arthritis. For anti-Sm and anti-RNP, IgG1 was the predominant isotype. For anti-ds-DNA and anti-SS-B, IgG1 and a lesser contribution of IgG3 was found. In contrast, IgG1 and IgG4 were the predominant isotypes of human IgG RF. The preponderance of isotypes noted for these autoantibodies did not extend to the IgG subclass distribution for antibodies to trinitrophenol-bovine serum albumin (TNP), tetanus toxoid (Tet. tox.), pneumococcal polysaccharides (Pneumo), and group A streptococcal cell walls (Strep.). The restriction of human humoral responses as well as autoantibodies has both pathogenetic and immunoregulatory implications, and suggests that for these autoantibodies, T-cell-dependent responses, probably driven by antigen, are of importance.