Unscheduled DNA synthesis in lymphocytes of rheumatoid arthritis patients and spleen cells of rats with experimentally induced arthritis.

DNA repair is an important factor in the abolition or manifestation of mutations. Since intrinsic somatic mutations may be related to the occurrence of autoimmunity, DNA repair was investigated by measuring unscheduled DNA synthesis in lymphocytes of rheumatoid arthritis patients by autoradiography. Likewise, unscheduled DNA synthesis was investigated in mycoplasma- and Freund's adjuvant-induced arthritis in rats. Both in human rheumatoid arthritis and experimentally-induced arthritis the capacity for repairing lesions in DNA induced by gamma-irradiation of cells was reduced, while an increased rate of thymidine-incorporation into DNA was found after UV-irradiation. The results are discussed in relation to endonucleases of viral or mycoplasmal origin.