[Levels of anti-nDNA using immunofluorescence on Crithidia luciliae. II. Prognostic value of complement-fixing anti-nDNA. Longitudinal study of 16 lupus disorders].

Measurements of the hemolytic complement level and titrations of anti dS DNA antibodies by immunofluorescence using Crithidia luciliae and by the Farr binding assay were performed in 13 females and 3 males suffering from systemic lupus erythematosus (SLE). In each patient, 2 to 5 serum samples were analyzed during a mean follow up time of 16.6 months. The complement fixing ability of the anti dS DNA antibodies was also investigated. In this longitudinal study the titers of the dS DNA antibodies detected by immunofluorescence correlated with the Farr binding assay results. Mean anti dS DNA antibody titers were significantly higher and CH 50 levels were lower when SLE was active. Among sera with anti dS DNA antibodies, only sera with high titers (greater than or equal to 1/80), fixed complement. Study of individual cases disclosed that an increase in complement fixing anti dS DNA antibodies could occur in the absence of disease activity. Sera from patients with severe organ involvement, in particular with nephritis had low titers of anti dS DNA antibodies with no complement fixation activity. There was no relationship between falls in serum complement level and the complement fixation ability of anti dS DNA antibodies. Thus, complement fixation capacity of anti dS DNA antibodies correlates better with antibody titer than with SLE severity or activity.