Genetic reconstitution of systemic lupus erythematosus immunopathology with polycongenic murine strains

Abstract

We previously produced three congenic strains carrying lupus susceptibility genes (Sle1-Sle3) from the lupus-prone NZM2410 mouse on the C57BL/6 background and characterized their component phenotypes. Sle1 mediates the loss of tolerance to nuclear antigens; Sle2 lowers the activation threshold of B cells; and Sle3 mediates a dysregulation of CD4(+) T cells. We have now created a collection of bi- and tricongenic strains with these intervals and assessed the autoimmune phenotypes they elicit in various combinations. Our results indicate that Sle1 is key for the development of fatal lupus. The combination of Sle1 with Sle2, Sle3, or the BXSB-derived autoimmune accelerating gene yaa results in the development of systemic autoimmunity with variably penetrant severe glomerulonephritis culminating in kidney failure. In contrast, two locus combinations of Sle2, Sle3, and yaa failed to mediate fatal disease. These results indicate that the loss of tolerance to chromatin mediated by Sle1 is essential for disease pathogenesis and identify the pathway occupied by Sle1 as a strategic target for therapeutic intervention in systemic lupus erythematosus. The coexpression of Sle1, Sle2, and Sle3 as a B6-triple congenic results in severe systemic autoimmunity and fully penetrant, fatal glomerulonephritis. These results demonstrate the fulfillment of the genetic equivalent of Koch's postulate, where susceptibility loci in a lupus-prone strain have been identified by a genome scan, isolated and functionally characterized by congenic dissection, and finally shown to mediate full disease expression when recombined in a normal genome.

Figure 1

Clinical lupus nephritis is reconstituted in B6-Sle1/Sle2/Sle3. (A) Cumulative mortality in the bicongenic and tricongenic strains, as compared with NZM2410. Not shown on the figure are the parental monocongenic strains and B6-Sle2/Yaa and B6-Sle3/Yaa, which did not suffer any mortality during the first year of life. A total of 30–90 mice were used per strain. (B) GN penetrance according to the predominant type of lesion—mesangial, hyaline, or proliferative. Only lesions affecting at least 25% of the glomeruli were included. Ten (for monocongenic strains) to 35 mice per strain were used. Only NZW females were used because the penetrance of GN in NZW males at 1 yr of age is extremely low (20). B6-Sle1 does not show any severe glomerular lesion at 12 mo of age (11).

Figure 2

Reconstitution of SLE serological defects with polycongenic combinations. (A) Anti-chromatin IgG Ab assayed in 7-mo-old sera. Each symbol represents a different mouse. (B) Glomerular-binding autoantibodies assayed in sera from 9–12 mo for the bicongenic and B6 mice, or 7–9 mo old for the triple congenic and B6-Sle1/Yaa mice; mean + SE, 10–15 mice per strain. (C) Penetrance of dsDNA IgG Ab production in 5-mo-old mice, 15–20 mice per strain.

Figure 3

Reconstitution of lymphocyte activation with polycongenic combinations. (A) Spleen weights at sacrifice, 15–25 mice per strain, means and SE. (B) Percent CD4⁺ splenocytes expressing CD69 and (C) mean fluorescence intensity of B7.2 on B220⁺ splenocytes in B6-Sle1/Sle3 and B6-Sle1/Sle2/Sle3 B6-Sle1/Sle2/Sle3; six males (□)and six females (▪) in each strain; means and SE.