Reversal of Lupus Nephritis by SAP Treatment Figure 4. pSAP administration in the early stage of SLE disease reverses ALD-DNA-induced lupus nephritis. BALB/c mice were immunized subcutaneously with ALD-DNA (50 mg/mouse) or PBS for total 3 times in 4 weeks. Mice immunized with ALD-DNA were administrated intramuscularly with pSAP (100 mg/mice) from week 4 after initial immunization (with the onset of proteinuria) and injected every 2 weeks for total 5 times. (A) The dynamics of SAP level in serum of lupus mice injected with pSAP (ALD-DNA plus pSAP) or pcDNA3 (ALD-DNA plus pcDNA3) were determined by ELISA assay every 2 weeks. (B) The dynamics of circulating DNA level in serum of lupus mice injected with pSAP (ALD-DNA plus pSAP) or pcDNA3 (ALD-DNA plus pcDNA3) were determined by ELISA assay every 2 weeks. (C) The ratios of SAP to DNA in SLE murine model injected with pSAP (ALD-DNA plus pSAP) or pcDNA3 (ALD-DNA plus pcDNA3) at week 12 after initial immunization. Data are means 6 SD from 10 mice in each group. ***, P,0.001. (D) Serum anti-dsDNA IgG levels of the mice were measured by ELISA assay every 2 weeks. (E) Anti-dsDNA IgG antibody titers in serum of pSAP-treated lupus mice (ALD-DNA plus pSAP) or pcDNA3-treated lupus mice (ALD-DNA plus pcDNA3) were detected by ELISA assay at week 8 after the initial ALD-DNA immunization. n = 10. (F) Urine protein levels of the mice were assessed by BCA Protein Assay Kit (Thermo Fisher Scientific) every 2 weeks. n = 10. (G) The deposition of IgG-containing IC in glomeruli at week 12 after initial immunization. Imagines (6200) are representative of at least 10 mice in each group. (H) Mean glomerular fluorescence intensity (arbitrary units) was determined for IgG in ALD-DNA- immunized lupus mice and control mice at week 12 after initial immunization. n = 10. **, P,0.01. (I) 12 weeks after initial immunization, nephritic pathological changes were shown by H&E staining of renal tissues surgical resected from the mice. Imagines (6200) are representative of at least 10 mice in each group. (J) The kidney score was assessed using paraffin sections stained with H&E. n = 10. ***, P,0.001. doi:10.1371/journal.pone.0022659.g004 contributes to the pathogenesis of SLE [20,21]. And the SAP- linked genes co-deficency may confuse the elucidation of the role of SAP in autoimmunity [22]. Therefore, study of SLE pathogenesis in regarding to SAP in a mouse model with clear genetic background is very critical and should be a prerequisite. Herein, we use ALD-DNA-induced SLE murine model to extensively study the role of SAP in SLE pathogenesis. In this study, it was found that the ratios of SAP to DNA significantly decreased in ALD-DNA-induced lupus mice as compared to controls. SAP plasmid (pSAP) treatment in vivo could significantly increase the levels of serum SAP and notably decreased the levels of circulating DNA, thus simultaneously increasing the ratios of PLoS ONE | www.plosone.org 8 July 2011 | Volume 6 | Issue 7 | e22659