Comparison of commercial kits for the detection of anti-nDNA antibodies using Crithidia luciliae.

The reactions of sera from 15 selected patients with connective tissue diseases and 4 selected control people were compared with the use of five commercial kits detecting anti-nDNA antibodies by indirect immunofluorescence on Crithidia luciliae. The cases with systemic lupus erythematosus (SLE) and a related condition reacted with the kinetoplasts of the C. luciliae in each kit tested with one exception, notably a case of drug-induced LE. The four control cases selected for a trace of staining of the nuclei of C. luciliae gave negative reactions with the kinetoplasts. The titer for each individual positive serum varied from 1.36 to 2.67 (mean SG 2.04) geometric standard deviation units. The staining pattern of sera positive for anti-nDNA antibodies on C. luciliae included reactivity of the kinetoplast with or without nuclear staining. The drug-induced LE serum produced only nuclear staining with no significant kinetoplast staining, i.e., a negative test for anti-nDNA antibodies. Patient control sera stained only the nucleus when any reactivity on C. luciliae was present. Generally, there were no major differences in titers and patterns of sera when comparisons were made between manufacturers. The sera were also tested by the Farr radioimmunoassay and the latex nucleoprotein test. The results of both of these assays correlated in most cases with the C. luciliae reactions.