To characterise IgG4 rheumatoid factor (RF) at the molecular level from a patient with rheumatoid arthritis.
B cells were cloned from the peripheral blood of a patient with rheumatoid arthritis, using EB virus transformation. The supernatants of the clones were screened for IgG RF activity by ELISA. Nucleotide sequences of the expressed immunoglobulin heavy and light chain genes of one IgG RF producing clone were determined by direct sequencing of the products of a polymerase chain reaction.
One clone producing monospecific IgG4 RF was obtained. Sequence analysis of the heavy and light chain genes suggested the accumulation of somatic mutations resulting in amino acid replacement in complementarity determining regions.
The results may suggest an antigen driven response in the generation of IgG4 RF in rheumatoid arthritis disease processes.