Phytohemagglutinin-stimulated lymphocytes from patients with systemic lupus erythematosus demonstrate DNA damage

DNA samples from control and lupus lymphocytes were studied for DNA integrity and single-strand breaks by agarose gel electrophoresis following digestion with the enzyme S1 nuclease. S1 nuclease digests single-strand gaps in double-stranded DNA. Gel patterns of phytohemagglutinin (PHA)-stimulated control and lupus lymphocyte DNAs were identical in the absence of S1 nuclease incubation. DNA isolated from PHA-stimulated control lymphocytes was relatively resistant to S1 nuclease digestion in 14 of 16 samples. However, 15 of 16 DNA samples from PHA-stimulated lupus lymphocytes demonstrated dramatically greater S1 nuclease digestion than paired control DNAs from lymphocytes analyzed at the same time under the same conditions. Increased S1 sensitivity suggests that more single-strand DNA breaks were found in PHA-stimulated lupus lymphocytes and/or the lupus DNA was more damaged than control DNA. We suggest that structural changes found in DNA from stimulated T lymphocytes of lupus patients are consistent with an endogenous antigen-mediated disorder.