Background/Purpose

In patients with lupus nephritis (LN), acute renal vascular and atherosclerotic lesions correlate with the degree of inflammation regardless the presence of antiphospholipid antibodies. The aim of this study was to confirm these results in MRL/lpr mice and to analyze the specific effect of blocking inflammatory factors and/or platelet aggregation.

Methods

The pattern of renal vascular disease, acute and chronic glomerular and tubulointerstitial lesions were specifically analyzed with histological staining (H&E, PAS) in 12-20-wk old female MRL/lpr mice with nephritis. Immunohistochemistry (IHC) techniques were used to detect CD41 (platelet aggregates), fibrinogen (FGN), periglomerular macrophagic F4/80 (quantified as the % of positive glomeruli), intraglomerular macrophage infiltration (Mac-2) and C3 deposition. Renal function was assessed by measuring proteinuria, serum creatinine and albumin (sCr, sAlb). Levels of a-dsDNA and anticardiolipin (aCL) antibodies were quantified by ELISA. The specific effect of treatment with steroids and antiaggregation (aspirin or clopidogrel) was analyzed. Association between categorical variables was tested by the Χ² test. For continuous variables, comparisons were carried out using t-test for two independent samples. A Spearman’s rank was used for correlations among different study parameters. P values < 0.05 were considered significant. 

Results

In the descriptive phase, 41 mice were analyzed. Histological, IHC and clinical characteristics of lpr mice with lupus nephritis are described in table 1.

Mice with microthrombotic renal vascular lesions showed a greater degree of periglomerular macrophage infiltration (p=0.002). All mice had detectable a-dsDNA or aCL IgG, irrespective of the presence of TMA or CD41+. Proteinuria positively correlated to the proportion of sclerotic glomeruli (r=0.4; p=0.01) and glomerular macrophage infiltration (r=0.46; p=0.004) and was higher in mice with diffuse proliferative glomerular lesions (340.8 vs110.8; p=0.02). 

After two weeks of treatment, the specific effect of 15 mg/d dexamethasone, 10 mg/d aspirin or 1.5 mg/d clopidogrel, or combined therapy dexa+ antiaggregation was compared to PBS treatment in 52 mice, and results are detailed in table 2.

Table 1

Mice (n=41)

Glomerular lesions:    Focal and segmental proliferative    Diffuse proliferative Interstitial fibrosis Instertitial inflammation:    Medular    Cortical    Both Mice with sclerotic glomeruli (number of glomeruli) Microthrombotic renal vascular lesions (thrombotic microangiopathy [TMA] or CD41+ microthrombi) Glomerular/extragomerular FGN (%) Glomerular Mac-2 (%) Periglomerular F4/80 (+ glom %) Mean sCr (mg/dl) Proteinuria (>300mg/dl)

–     53.7% 46.3% 5% –   7.3% 29.3% 36.6% 46% (1-11) 34% –    4.8 ± 3.6/0.8 ± 0.6 3.9 ± 2.3 41.9 ± 21.4 0.5 ± 0.1 13.2%

Table 2

	PBS	dexamethasone (15 ug/d)	aspirin /clopidogrel (10 o 1,5 mg/d)	dexamethasone and antiaggregation
Exp1	N=8	N=9 ↓ proteinuria ** ↓a-dsDNA** = aCL = sCr and sAlb ↓CD41 (NS) = C3 deposition ↓Mac-2* ↓F4/80**	N=8 ↓ proteinuria ** ↓a-dsDNA* ↓aCL* = sCr and sAlb ↓CD41 (NS) ↓C3 deposition* ↓Mac-2* ↓F4/80**	N=8 ↓ proteinuria* ↓ a-dsDNA** ↓ aCL* = sCr and sAlb ↓ CD41 (NS) = C3 deposition ↓Mac-2* ↓F4/80**
Exp2	N=4	N=4 ↓proteinuria* ↓ a-dsDNA * = aCL = sCr and sAlb ↓CD41 (NS) = C3 deposition ↓Mac-2* ↓F4/80*	N=6 ↓proteinuria** ↓ a-dsDNA* = aCL = sCr and sAlb ↓CD41 (NS) ↓C3 deposition* ↓Mac-2** ↓F4/80**	N=5 ↓ proteinuria** ↓ a-dsDNA (NS) ↓ aCL (NS) = sCr and sAlb ↓CD41 (NS) ↓C3 deposition* ↓Mac-2* ↓F4/80*
Both	N=12	N=13 ↓proteinuria*** ↓ a-dsDNA* = aCL = sCr and sAlb ↓CD41 (NS) = C3 deposition ↓Mac-2*** ↓F4/80***	N=14 ↓proteinuria*** = a-dsDNA = aCL = sCr and sAlb ↓CD41 (NS) ↓C3 deposition** ↓Mac-2*** ↓F4/80***	N=13 ↓ proteinuria** ↓ a-dsDNA* ↓ aCL** = sCr and sAlb ↓CD41 (NS) ↓C3 deposition* ↓Mac-2** ↓F4/80***

*: p<0.05; **:p<0.01; ***: p<0.001; NS: no significant

Conclusion

Presence of microthrombotic renal vascular lesions is associated to a higher degree of macrophage infiltration in MRL/lpr model of LN. Both dexamethasone and blockers of platelet aggregation reduce glomerular damage and inflammatory response, suggesting platelets involvement in inflammatory damage.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/microthrombotic-renal-vascular-lesions-are-associated-to-increased-renal-inflammatory-infiltration-in-a-mouse-model-of-lupus-nephritis/