A study of the variable heavy chain (VH) regions in human polyclonal IgM rheumatoid factors

Ten IgM polyclonal rheumatoid factor (RF) preparations isolated from sera from various patients with rheumatoid arthritis (RA) were investigated with respect to their variable heavy chain (VH) subgroups. They were tested in a haemagglutination inhibition system using red cells sensitized with myeloma proteins with known chemical VH subgroups and anti-VH subgroup specific antisera. Most of the preparations showed a considerable degree of restriction to one VH subgroup. Seven of the IgM-RF preparations were restricted to the VHIII subgroup, two to the VHI subgroup and one to the VHII subgroup. However, a weak reaction in other VH subgroup systems was seen in several instances. Two normal IgM fractions from healthy persons showed no VH subgroup restriction, and showed a rather similar degree of reaction in all the three subgroup systems.