Anti-ribosomal-P antibodies in lupus patients and healthy controls: evaluation of three ELISA assays.

BACKGROUND Anti-ribosomal-P antibodies have been associated with central nervous system manifestations of systemic lupus erythematosus. However, inconsistencies in their prevalence and clinical correlations have become an obstacle to their use as a diagnostic marker of the disease. This lack of consistency might stem from several factors, such as the lag period between clinical manifestations and the time blood was drawn; or the different methods used for antibodies detection. OBJECTIVES To evaluate three different enzyme-linked immunosorbent assay tests for the detection of anti-Rib-P Abs in patients with SLE and in normal controls. METHODS Sera from 50 SLE outpatients and 50 healthy subjects were tested with three ELISA kits: Kit-1, using synthetic peptide comprising the 22 C-terminal aminoacids; Kit-2, using native human ribosomal proteins (P0, P1, P2); and Kit-3, which is coated with affinity-purified human ribosomal proteins. ELISA studies were performed according to the manufacturers' instructions. RESULTS The prevalence of anti-Rib-P Abs in SLE patients and controls was 30% vs. 0%, 17% vs. 21%, and 30% vs. 14% in kits 1-3 respectively. Anti-Rib-P Abs detected by Kit-1 correlated with the SLEDAI score (SLE Disease Activity Index). No correlation between prior CNS manifestations and anti-Rib-P Abs was observed. CONCLUSIONS A significant difference was documented between the ELISA kits used for the detection of anti-Rib-P Abs. A correlation was found between these antibodies (evaluated by Kit-1) and concurrent SLEDAI scores, in contrast to the lack of correlation with previous CNS manifestations. This supports the notion of "active serology" that is evaluated at the same time manifestations are present, as well as the need for standardization of laboratory assays in the future which will enable a better assessment of anti-Rib-P Abs presence and clinical significance.