Background/Purpose:

Immune-mediated glomerulonephritis is a serious end organ pathology that commonly affects patients with systemic lupus erythematosus (SLE). Nephrotoxic serum nephritis, induced by passive transfer of preformed nephrotoxic antibodies, is a mouse model commonly used to study lupus nephritis (LN). We and others have previously shown that macrophages are important in the pathogenesis of LN. To further delineate critical nephritis-associated pathways, in this study we assessed the importance of NF-kB signaling in the myeloid cell lineage in the pathogenesis of LN.

Methods:

Using flox-cre technology, we created a novel B6 mouse strain with genetic deficiency in RelA (aka p65) restricted to myeloid cells (RelA flox/flox LyzM cre/cre B6; KO mice), thus facilitating the study of the role of classical NF-kB signaling in myeloid cells in the context of immune mediated nephritis. Lupus like nephritis was induced at 9-10 weeks of age in both the KO mice and age-matched wildtype control B6 mice (WT mice). Mice were immunized on day 0 with rabbit IgG emulsified in complete Freund’s adjuvant, and 5 days later were given the nephrotoxic serum (containing rabbit antibodies which target murine glomerular antigens) by intravenous injection. Mice were then serially assessed for the development of nephritis.

Results:

By day 13, myeloid cell RelA KO mice (n=14) injected with nephrotoxic serum had significantly attenuated proteinuria (mean protein:creatinine ratio KO=3.1 ± 2.2 vs. WT=29.0 ± 9.0, p<0.05) and lower serum BUN levels (mean KO= 46.0 ± 5.7 mg/dL vs. WT 69.9 ± 6.2 mg/dL, p<0.01) compared to control injected WT mice (n=16). Inhibiting myeloid NF-κB signaling also decreased inflammatory modulators within the kidneys. We found significant decreases in expression of IL-1a, IFNg, and IL-6 in kidneys from KO mice, but higher IL-10 expression. We also found a significant reduction of macrophages accumulating in the kidney by immunofluorescent staining, a finding confirmed by flow cytometry. Specifically, flow cytometric analysis revealed decreased numbers of classically activated macrophages infiltrating the kidneys of KO mice. Kidney IgG and C3 deposition, however, was not different between KO and WT mice. Additionally, the two strains had no differences in their antibody response to the initial immunization (in both total IgG concentration and concentrations of different isotypes), indicating that any differences in disease severity were not because deficient myeloid NF-κB signaling interfered with disease induction. Analysis of renal histopathology is pending.

Conclusion:

Our studies indicate that macrophage NF-κB signaling is instrumental in the contribution of this cell type to the pathogenesis of nephritis induced by pathogenic antibodies. These results suggest that while approaches which decrease macrophage numbers can be effective in LN, more targeted treatments directed at modulating macrophage signaling and/or function could be beneficial, at least in early stages of the disease.

« Back to 2018 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/nf-%ce%baappa-b-signaling-in-the-myeloid-cell-lineage-drives-the-pathogenesis-of-immune-mediated-nephritis/