| Abstract: | Hidden 19S IgM rheumatoid factors (RF), i.e., 19S IgM RF which can be detected in the IgM containing fraction after acid gel filtration of serum, are found in 59-68% of patients with juvenile rheumatoid arthritis (JRA). Their presence generally correlates with disease activity. We describe a 12 year-old female with a polyarticular onset of JRA who, during her first 15 months of disease, was seronegative but had hidden RF titers of 1:128----1:256. Inhibition studies on her hidden RF showed specificity for HIgG greater than RIgG and equal specificity for the human IgG subclasses (IgG1 = IgG3). In the second and third year of disease, she became seropositive with RF titers varying from 1:40 to 1:320 while her hemolytic titers on her IgM fractions were decreased from 1:128 to 1:32. Inhibition studies now demonstrated a higher avidity for RIgG; and HIgG3 inhibited more than HIgG1. These studies documented for the first time a JRA patient who early in the disease was negative for RF and positive for hidden RF, and who later became seropositive. |
