Hidden and classical 19S IgM rheumatoid factor in a juvenile rheumatoid arthritis patient.

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).

Autoantibodies in juvenile arthritis.

Sera from 104 children with JA with different onset-types of disease were evaluated for 19S IgM RF by the LFT , hidden 19S IgM RF by the hemolytic assay, ANA by HEp-2 cell substrate, and levels of IC by the C1qSPA . Their relationship to active disease was determined. Classical 19S IgM RF were detected by the LFT in only seven patients.