Immunogenic and antigenic epitopes of immunoglobulins. VIII. A human monoclonal rheumatoid factor having specificity for a discontinuous epitope determined by histidine/arginine interchange as residue 435 of immunoglobulin G.

A monoclonal human rheumatoid factor (RF-AN) reactive with human Fc gamma is shown to recognise a discontinuous epitope dependent on the presence of histidine (His) at residue 435. RF-AN is not reactive with IgG1 paraproteins having C gamma 2 or C gamma 3 domain deletions or IgG3m (5) or Ig3m (21) proteins having arginine (Arg) at residue 435. RF-AN is reactive with IgG1, 2, 4 and IgG3m (15,16) proteins having histidine at 435.