Inheritance of immunoglobulin M rheumatoid-factor idiotypes.

The idiotypic determinants on IgM rheumatoid factor (RF) from a single family have been analyzed. Rabbit Fab'2 antiidiotypic antibody was prepared against purified IgM-RF from a patient with rheumatoid arthritis. As measured by radioimmunoassay, the antiidiotype reacted with at least 90% of the patient's RF, but not with non-RF immunoglobulins from the same serum, nor with 10 of 11 polyclonal and monoclonal RF from unrelated individuals. Cross-reacting idiotypes were detected on RF in four of the patients' first degree relatives, spanning three generations, without apparent relation of HLA type or clinical rheumatoid arthritis. These results suggest that IgM-RF associated idiotypes were inherited in this family.