BackgroundThe levels of IL-33, a Th2 promoting cytokine, and the soluble form of its receptor ST2 were reported to be elevated in serum of patients with active systemic lupus erythematosus (SLE), suggesting a role of the IL-33/ST2 axis in the pathogenesis of SLE.ObjectivesThis study aims to examine the effect of IL-33 in disease severity of murine lupus.MethodsIL-33 was injected intraperitoneally 3 times per week to pre-diseased MRL/lpr mice aged 12 weeks for 6 weeks. Control group was given 1% BSA injection. Urine protein was monitored weekly by albustix and protein assay. Immunophenotyping of splenocytes was examined by flow cytometry. Splenic CD11b+monocytic cells were isolated by microbeads for mRNA examination.ResultsIL-33-treated mice (n=9) developed significantly less proteinuria compared to BSA-treated group (n=9). Kidney histology of the IL-33-treated group showed remarkably less mesangial deposit, diffuse proliferative glomerular changes and crescents, and had significantly lower renal composite score compared to controls (median 2.0 vs 9.9, p<0.001). Kidneys of these mice expressed lower mRNA levels of TNF-α (32.1±14.7 vs 77.0±27.8, p<0.001), IL-6 (median 0.6 vs 4.7, p=0.003), IL-1β (31.1±10.1 vs 77.8±24.6, p<0.001) and iNOS (p=0.006). Immunophenotyping of splenocytes showed significantly increased CD4 +CD25+regulatory T (Treg) cells (4.0%±1.2% vs 2.2±0.2%, p<0.001) that expressed remarkably higher Foxp3 (76.0%±5.0% vs 59.3±12.6%, p=0.002). Splenic extracts showed predominant Gata3 (0.37±0.20 vs 0.12±0.09, p=0.01) and Foxp3 (0.42±0.16 vs 0.17±0.11, p=0.002) mRNA in IL-33-treated mice. These Treg cells expressed high cell surface ST2 (8.9%±2.7% vs 4.5±2.0%, p=0.008). There was significant expansion of splenic CD11b+population in IL-33-treated mice (17.8±10.5 vs 8.8±3.0, p=0.01) that expressed significantly higher CD206 (5.2%±0.9% vs 2.9±0.9%, p=0.002). Isolated splenic CD11b+cells expressed significantly higher mRNA of Arg1, FIZZI and Ym-1 and IL-10 (all p=0.01) with reduced expression of iNOS (p=0.02). Kidney extracts of IL-33 treated mice also had elevated mRNA levels of M2 markers including Arg1 (median 199.8 vs 36.1, p=0.004) and FIZZI (median 25.0 vs 2.7, p<0.001) and reduced MCP-1 (12.7±6.5 vs 35.1±12.0, p<0.001). There was also significantly higher levels of mRNA of Foxp3 (median 43.0 vs 20.8, p=0.006) and Gata 3 (1.7±0.5 vs 0.9±0.5, p=0.008) but lower Rorc (2.6±1.0 vs 3.8±0.8, p=0.008) and Tbx21 (12.6±6.0 vs 29.6±13.7, p=0.003) in the kidneys.ConclusionsExogenous IL-33 led to significantly less proteinuria and renal inflammation. These mice had significantly higher splenic Treg cells with prominent Foxp3 expression. Isolated CD11b+cells from spleen and kidney extracts demonstrated mRNA levels of M2 macrophage polarisation.Disclosure of InterestNone declared
