Restricted light chain subgroup expression on human rheumatoid factor paraproteins determined by monoclonal antibodies.

Two hybridoma antibodies specific for determinants on the V kappa light chain subgroup have been produced and characterized. Antibodies C7 and B12 reacted with distinct V kappa epitopes irrespective of association with heavy chain class or subclass. Epitopes recognized by C7 and B12 were expressed on the light chain of IgG, IgA, and IgM and Bence-Jones paraproteins from the V kappa subgroup. However, a preferential association of both epitopes with IgM RF paraproteins was demonstrated. Hybridomas C7 and B12 reacted with 12/12 and 10/12 IgM RF paraproteins, respectively, but only with 3/6 IgM paraproteins, with no RF activity. Both epitopes C7 and B12, were immunodominant and conformation dependent, being detected by HA, HAI and ELISA on intact light chain but not isolated VK.