Reevaluation of specificity of Crithidia luciliae kinetoplast as a substrate for detecting antibodies to double-stranded deoxyribonucleic acid.

Until now, the kinetoplast of the hemoflagellate Crithidia luciliae has been believed to be a specific indirect immunofluorescence substrate for detecting antibodies to double-stranded deoxyribonucleic acid (DNA). We have recently identified a patient in whom there was the apparent presence of procainamide-induced antinuclear antibodies at a titer of 1/1,280 on mouse kidney sections. This patient's serum also contained antihistone antibodies at a titer of 1:1,280, on the basis of a mouse kidney section histone reconstitution assay. In addition, results of an enzyme-linked immunosorbent assay (ELISA) using a pure histone preparation were strongly positive. We found that this serum produced C. luciliae fluorescence to a titer of 1:80. After pretreatment of the C. luciliae substrate with hydrochloric acid to remove histones, this serum no longer produced kinetoplast fluorescence. However, this serum again produced kinetoplast fluorescence when assayed on a hydrochloric acid-treated C. luciliae substrate that had been reconstituted with purified histone. The negative kinetoplast reactivity after hydrochloric acid treatment of the C. luciliae substrate suggests that the antibody is reacting with acid-extractable nucleic acids, not necessarily the double-stranded DNA, or the antibody is directed against nuclear proteins such as DNA-histone complexes of deoxyribonucleoprotein. The finding that reactivity reappeared after the histone was reconstituted back to the hydrochloric acid-treated C. luciliae substrate suggests that the primary antibody in this serum is directed against DNA-histone complexes or histone alone. These findings strongly suggest that the kinetoplast of C. luciliae contains antigens other than double-stranded DNA and that is not a specific substrate for the detection of double-stranded DNA antibodies by indirect immunofluorescence.