Determination of human immunoglobulin M rheumatoid factor by a solid-phase radioimmunoassay which uses human immunoglobulin G in antigen-antibody complexes.

A solid-phase radioimmunoassay for the rapid determination of human immunoglobulin M (IgM) rheumatoid factor (RF) has been developed. Preparation of the solid phase for the assay involved the formation of complexes between respiratory syncytial virus-specific human IgG antibodies and virus antigen on the surface of polystyrene balls. Binding of serum RF to IgG in the immune complex was subsequently detected by 125I-labeled mu-chain-specific antibodies to human IgM. The amount of radioactive indicator antibody bound was converted to units of RF by comparison to the standard curve for an RF reference-serum pool. This assay should prove useful in studies of the physiological role of RF, since it can effectively measure low levels of circulating RF.