Demonstration of a cross-reactive idiotype (IdRQ) in rheumatoid factors from patients with rheumatoid arthritis but not in rheumatoid factors from healthy, aged subjects.

A human monoclonal IgM kappa paraprotein with rheumatoid factor (RF) activity was used to elicit antiidiotypic antibodies in rabbits. The antiidiotypic antiserum thus obtained reacted with samples from 40% of 72 rheumatoid arthritis patients, but not with any of the samples from 22 aged control subjects having serum RF. Our findings suggest that, despite the similarities between RF from rheumatoid arthritis patients and that from healthy individuals, the expression of V region genes may be different in healthy subjects and those with the disease.