Common IgA and IgM rheumatoid factor idiotypes in autoimmune diseases.

Anti-idiotypic antibodies to four monoclonal IgM, one polyclonal IgM, and one polyclonal IgA rheumatoid factors were produced in rabbits and tested for cross reactivity with rheumatoid factors from nine patients with essential mixed cryoglobulinaemia, three patients with rheumatoid arthritis, four patients with systemic sicca syndrome, and one patient with systemic lupus erythematosus. Variable (3/16 to 10/16) cross reactivity for each anti-idiotypic antibody was observed which was not restricted by disease category, clonality, or isotype of the rheumatoid factor. These findings suggest that rheumatoid factor genes are highly conserved from the germ-line antibody repertoire.