Nucleotide Sequences Specific for Nonnominal Immunoglobulin Allotypes in Rheumatoid Arthritis Patients and in Normal Individuals and Their Expression in Synovial Tissue of Rheumatoid Arthritis Patients

Abstract

The production of antibodies against nonnominal immunoglobulin allotypes in rheumatoid arthritis (RA) patients suggests that the immune system of these patients has been exposed to such foreign allotypes. The presence of nonnominal allotypes is, however, a genetic enigma. We searched for nucleotide sequences specific for nonnominal G3m^g and G3m^b copies in individuals homozygous for these alleles. Using a sensitive and specific nested polymerase chain reaction (PCR) method with genomic DNA from blood of 18 RA patients and 5 normal controls, we found G3m^g sequences in 18 of 18 tested G3m^b homozygous persons. The allele specificity of the PCR fragments was confirmed by sequencing and RFLP analysis. The PCR products contained genomic nonspliced parts of the nonnominal sequences. An analysis of cDNA from inflammatory tissue of 5 RA patients detected nonnominal G3m^b sequences in 1 of 3 tested G3m^g homozygotes and G3m^g sequences in 2 of 2 tested G3m^b homozygotes. The cDNA-derived PCR products contained sequences from normally spliced nonnominal Ig fragments. The results also showed that the nonnominal Ig sequences were present in very low copy numbers, lower than the Mendelian 1–2 copies per cell. The origin of such a low copy number of Ig gene fragments may be explained by a virus-mediated capture and transfer mechanism of Ig gene fragments generated by the normal Ig switch-associated gene excision process.

Rheumatoid Arthritis – A Gene Transfer Disease

“…However, our observations of the hidden allotype genes [30] show that the DNA sequences for the hidden allotypes are present in normal genomic configurations and that the fragment is normally spliced in the expressed form. It is thus not likely that the hidden allotype genes are transported by a retrovirus.…”

“…Starting with model experiments, we have focused on the G3m(b) and (g) allotypes because their restriction endonuclease cleavage sites are well known [24]. Recently, by nested PCR, we have for the first time defined hidden allotypes at the genomic level [30]. We also observed that the number of copies of these genes is so small that a Mendelian inheritance is excluded.…”

“…We have recently shown that hidden allotype genes are in fact expressed in the synovial tissue of RA patients [30]. The foreign genes when expressed make incompatible allotypes and this in turn gives rise to the immune response observed as the anti-Gms in RA patients.…”

A Mathematical Model of Disease

“…Therefore, detecting antibodies with a foreign allotype indicates the immunological activity of microchimeric cells. For instance, patients with rheumatoid arthritis were found to produce antibodies targeting foreign immunoglobulin allotypes [57,58]. Moreover, the corresponding genes of these extrinsic immunoglobulins were detected in synovial tissues by polymerase chain reaction, suggesting a microchimerism involvement [57].…”