IgM rheumatoid factors in patients with rheumatoid arthritis derive from a diverse array of germline immunoglobulin genes and display little evidence of somatic variation.

Rheumatoid factors (RF) are present in the plasma of patients with rheumatoid arthritis (RA) although the site of synthesis of most of these antibodies is within the synovium. This report primary concerns RF of the IgM isotype. While a few of the RF derive from patients with systemic lupus erythematosus or from normal individuals, the remaining derive from the inflamed synovial tissue of patients with RA. Two RF are encoded by members of the VH1 gene family, 8 from the VH3 family and 2 from the VH4 family. Two polyreactive antibodies derive from the VH3 family and 2 come from the VH4 family. This distribution is not fundamentally different from the distributions seen in a large array of autoantibodies and antibodies to external antigens. Similarly, the light chains derive from most of the known kappa and lambda VL families. It is hard to escape the preliminary conclusion that gene segments from virtually any light chain variable region can contribute to RF or polyreactive antibody structures. Most IgM RF and polyreactive antibodies are direct copies of germline genes in one of their polypeptide chains or at most are 2 nucleotides away in one of their chains from a known germline gene.