STAT4 deficiency reduces autoantibody production and glomerulonephritis in a mouse model of lupus
Introduction
A number of studies in patients and in murine models have reported that lupus is associated with the dysregulation of a wide variety of cytokines [1]. Within the well-characterized (NZB × NZW)F1 (BWF1) and its NZM derivative mouse models, conflicting results have been reported regarding the respective roles of IFNγ and IL-4, as the prototypic cytokines of the T helper 1 and 2 (Th1 and Th2) effector pathways. In BWF1 mice, over-expression of IFNγ, but not IL-4, significantly enhanced disease severity [2], and the immunosuppressive agent FK506 prevented lupus nephritis by suppressing IL-2 and IFNγ, but not IL-4 nor IL-10 production [3]. On the other hand, impairment of IL-4 signaling, either with anti-IL-4 Ab treatment or STAT6 deficiency dramatically ameliorated kidney disease in the NZM2410 and NZM2328 strains, in spite of the presence of high levels of anti-dsDNA antibodies [4], [5]. In these NZM strains, however, STAT4 deficiency was associated with a worsening of clinical nephritis in spite of an absence of anti-dsDNA Ab. These results suggested a differential role of cytokines in lupus pathogenesis, with Th1 cytokines supporting anti-dsDNA Ab production, and Th2 cytokines promoting glomerulosclerosis.
To dissect the genetic mechanisms by which these cytokines regulate lupus pathogenesis, we have introduced STAT4 or STAT6 deficiency on the B6.NZM.Sle1.Sle2.Sle3 (B6.TC) lupus-prone mouse. This triple congenic strain contains the three NZM2410 lupus susceptibility loci Sle1, Sle2, and Sle3 that are necessary and sufficient to reconstitute a fully penetrant lupus pathogenesis on a C57BL/6 (B6) background [6], and constitutes a simplified lupus genetic model since it contains only about 6% of the NZM2410 genome. The phenotypes of B6.TC.Stat4−/− and B6.TC.Stat6−/− mice were in sharp contrast with those found by others in NZM2410.Stat4−/− and NZM2410.Stat6−/−, in that anti-dsDNA Ab production was reduced by both STAT4 and STAT6 deficiency, but renal pathology was significantly reduced only by STAT4 deficiency. Multiple disease markers in various cellular compartments were restored to B6 levels in B6.TC.Stat4−/−, which suggests that abnormal IL-12/STAT4 signaling is responsible for these phenotypes in B6.TC mice.
Section snippets
Mice
The production of the B6.Sle1.Sle2.Sle3 (B6.TC) has been previously described [6]. B6.TC.Stat4−/− and B6.TC.Stat6−/− mice were produced using a marker-assisted strategy [7] to introgress the Stat4 or Stat6 null allele from the BALB/c.Stat4−/− or BALB/c.Stat6−/− strains (obtained from the Jackson Laboratory), respectively. BALB/c alleles were selected against using markers polymorphic between B6 and BALB/c, and mice used in this study were at ≥N8 backcross to the B6 background. B6 mice were
STAT4 and STAT6 deficiency affects the distribution of lymphocyte subsets in B6.TC mice
STAT4 and STAT6 deficiency resulted in significant changes in hemapoietic cell expansion and distribution in B6.TC mice (Table 1). Spleen weights were significantly reduced in both cases, although without reaching B6 levels (mean ± SD: 87 ± 9 mg), and were lower in B6.TC.Stat4−/− than in B6.Stat6−/− mice (P = 0.02). B6.TC mice are characterized with an elevated CD4/CD8 ratio due to Sle3-mediated impaired activation induced cell death [14] and an increased level of CD4+ T cell activation [6].
Discussion
We have shown in this study that STAT4 deficiency greatly reduced clinical disease severity, and dramatically affected the expression of most disease markers in the lupus prone B6.TC mouse. Through the detailed analyses of NZM2410 congenics, we have shown that the Sle1, Sle2, and Sle3 loci mediate lupus susceptibility through intrinsic defects in B and T lymphocytes and myeloid cells [17], [19], [20]. Our results here show that STAT4 deficiency normalizes the phenotypes of all these 3 cellular
Acknowledgment
This work was supported by an NIH grant RO1-AI058150 (L.M.).
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