Detection of the major rheumatoid factor cross-reactive idiotype precedes human IgG binding activity in a patient with polyarticular juvenile rheumatoid arthritis

A patient with polyarthritis and subcutaneous nodules was studied for expression of rheumatoid factors (RF) by numerous techniques for 5 months after presentation. Assays for RF binding human or rabbit IgG in whole sera, assays for hidden RF binding human or rabbit IgG, and assays for expression of the major RF cross-reactive idiotype (RCRI) in whole sera or by pokeweed mitogen induced plasma cells were performed (PWM-PC). In this patient, increased expression of RCRI in sera and among PWM-PC preceded detectable RF binding human IgG, and paralleled hidden RF and RF binding rabbit IgG expression.