Abstract: Objective To explore the characteristics of DNA antigen deposited in the skin lesions of patients with lupus erythematosus (LE). Methods Thirty-two LE skin specimens were collected. The deposited immune complexes were obtained by cryoprecipitation methods. Then the samples were digested by protease. Finally DNA was extracted with phenol and chloroform. The size of DNA fragments was detected on agarose gel electrophoresis. Ten kinds of probes were used to analyze the origin of these DNA molecules by dot hybridization. Results DNA fragments were successfully isolated from 27 skin specimens with four kinds of different sizes including band-I (20 000 bp), band-Ⅱ (1 300 bp), band-Ⅲ (800-900 bp) and band-Ⅳ (100-120 bp). In 15 specimens most of DNA was identified as band-I. In 2 specimens band-Ⅰ, -Ⅱ and -Ⅲ were all noticed, while all four bands were detected in 10 specimens. There was a positive correlation between small-sized fragments (100-200 bp) and disease activity (P<0.05, r=0.429). The hybridization showed a significant homology between the isolated DNA fragments and human genomic DNA. There was homology between the DNA fragments isolated from different individuals. Conclusions DNA and its immune complexes might contribute to the pathogenesis of skin lesion of LE. The sizes of these DNAs are 100 bp to 20 000 bp, which may be endogenous. Small sized DNA fragments may be more pathogenic and related to disease activity.

Key words: Lupus erythematosus, systemic, DNA, Antigen-antibody complex