Background Studies looking for clinical association of anti-ribosomal P (anti-P) autoantibodies and lupus nephritis (LN) describe contradictory results. It is clear that anti-dsDNA antibodies contribute to LN pathogenesis and their titers fluctuate together with those of anti-P, suggesting a linked generation or an anti-dsDNA cross-reaction with the P antigen. We reexamined the anti-P involvement in LN in relation with the possibility of anti-dsDNA and anti-P cross-reactivity

Methods Anti-P and anti-dsDNA were analyzed by ELISA. SLE sera (n=24) from patients with and with no LN were divided into 4 groups: A (anti-dsDNA positive, anti-P negative), B (both positive), C (anti-dsDNA negative, anti-P positive) and D (both negative). Anti-dsDNA cross-reaction was assessed against recombinant wild type and P-epitope-lacking P0 proteins using purified IgGs from SLE patients. Anti-P cross-reaction with dsDNA was analyzed testing affinity purified anti-P antibodies with an anti-dsDNA ELISA. LN biopsies (n=26) were classified according to ISN/RPS and relations to the anti-dsDNA and anti-P simultaneous presence were examined

Results Neither anti-dsDNA nor anti-P antibodies showed evidence of cross-reaction in any of the applied tests. LN biopsy proven patients: age (media±SD) 34±11 years; 88% female. No LN histologic class with anti-P relationship was observed: 9 patients had Class V (pure n=2) or mixed with Class III/IV (n=7); 1 patient was anti-P positive (p value>0.05). Two patients with LN had neither anti-dsDNA nor anti-P antibodies. The NIH Activity Index (8.9±4.9) and NIH chronicity index scores (1±1.1) and tubule-interstitial lesions were similar between anti-P positive or negative LN patients

Conclusions Cross-reactivity between anti-dsDNA and anti-P antibodies cannot explain the contradictory results of anti-P association with LN. Based on the present and our previous studies failing to find anti-P association with LN, it seems unlikely that anti-P contribute to the renal damage. Other factors beyond anti-dsDNA and anti-P might participate in LN

Funding Source(s): FONDECYT grant # 1160513 and CONICYT Basal grant # AFB170005