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A specific biomarker that can separate active renal vasculitis from other causes of renal dysfunction is lacking, with a kidney biopsy often being required. Soluble CD163 (sCD163), shed by monocytes and macrophages, has been reported as a potential biomarker in diseases associated with excessive macrophage activation. Thus, we hypothesized that urinary sCD163 shed by crescent macrophages correlates with active glomerular inflammation. We detected sCD163 in rat urine early in the disease course of experimental vasculitis. Moreover, microdissected glomeruli from patients with small vessel vasculitis (SVV) had markedly higher levels of CD163 mRNA than did those from patients with lupus nephritis, diabetic nephropathy, or nephrotic syndrome. Both glomeruli and interstitium of patients with SVV strongly expressed CD163 protein. In 479 individuals, including patients with SVV, disease controls, and healthy controls, serum levels of sCD163 did not differ between the groups. However, in an inception cohort, including 177 patients with SVV, patients with active renal vasculitis had markedly higher urinary sCD163 levels than did patients in remission, disease controls, or healthy controls. Analyses in both internal and external validation cohorts confirmed these results. Setting a derived optimum cutoff for urinary sCD163 of 0.3 ng/mmol creatinine for detection of active renal vasculitis resulted in a sensitivity of 83%, specificity of 96%, and a positive likelihood ratio of 20.8. These data indicate that urinary sCD163 level associates very tightly with active renal vasculitis, and assessing this level may be a noninvasive method for diagnosing renal flare in the setting of a known diagnosis of SVV.

Current biomarkers of renal disease in systemic vasculitis lack predictive value and are insensitive to early damage. To identify novel biomarkers of renal vasculitis flare, we analysed the longitudinal urinary metabolomic profile of a rat model of anti-neutrophil cytoplasmic antibody (ANCA) vasculitis. Wistar-Kyoto (WKY) rats were immunised with human myeloperoxidase (MPO). Urine was obtained at regular intervals for 181 days, after which relapse was induced by re-challenge with MPO. Urinary metabolites were assessed in an unbiased fashion using nuclear magnetic resonance (NMR) spectroscopy, and analysed using partial least squares discriminant analysis (PLS-DA) and partial least squares regression (PLS-R). At 56 days post-immunisation, we found that rats with vasculitis had a significantly different urinary metabolite profile than control animals; the observed PLS-DA clusters dissipated between 56 and 181 days, and re-emerged with relapse. The metabolites most altered in rats with active or relapsing vasculitis were trimethylamine N-oxide (TMAO), citrate and 2-oxoglutarate. Myo-inositol was also moderately predictive. The key urine metabolites identified in rats were confirmed in a large cohort of patients using liquid chromatography–mass spectrometry (LC-MS). Hypocitraturia and elevated urinary myo-inositol remained associated with active disease, with the urine myo-inositol:citrate ratio being tightly correlated with active renal vasculitis.

A specific biomarker that can separate active renal vasculitis from other causes of renal dysfunction is lacking, with a kidney biopsy often being required. Soluble CD163 (sCD163), shed by monocytes and macrophages, has been reported as a potential biomarker in diseases associated with excessive macrophage activation. Thus, we hypothesized that urinary sCD163 shed by crescent macrophages correlates with active glomerular inflammation. We detected sCD163 in rat urine early in the disease course of experimental vasculitis. Moreover, microdissected glomeruli from patients with small vessel vasculitis (SVV) had markedly higher levels of CD163 mRNA than did those from patients with lupus nephritis, diabetic nephropathy, or nephrotic syndrome. Both glomeruli and interstitium of patients with SW strongly expressed CD163 protein. In 479 individuals, including patients with SW, disease controls, and healthy controls, serum levels of sCD163 did not differ between the groups. However, in an inception cohort, including 177 patients with SW, patients with active renal vasculitis had markedly higher urinary sCD163 levels than did patients in remission, disease controls, or healthy controls. Analyses in both internal and external validation cohorts confirmed these results. Setting a derived optimum cutoff for urinary sCD163 of 0.3 ng/mmol creatinine for detection of active renal vasculitis resulted in a sensitivity of 83%, specificity of 96%, and a positive likelihood ratio of 20.8. These data indicate that urinary sCD163 level associates very tightly with active renal vasculitis, and assessing this level may be a noninvasive method for diagnosing renal flare in the setting of a known diagnosis of SW.

ObjectivesGranulocyte colony stimulating factor (GCSF) is important in mobilising neutrophils from the bone marrow but also has a range of proinflammatory effects. We therefore decided to investigate the role of GCSF in antineutrophil cytoplasmic antibody (ANCA) vasculitis.MethodsWe measured GCSF levels in the serum of 38 patients with active ANCA vasculitis compared with 31 age-matched controls, and assessed the effect of GCSF priming on the response of human neutrophils to ANCA. We also examined the effect of exogenous GCSF administration in a murine model of antimyeloperoxidase (anti-MPO) vasculitis, and the effect of GCSF on murine neutrophil activation.ResultsThe serum levels of GCSF in patients with active ANCA vasculitis were significantly higher than those of age matched healthy controls (mean 38.04 vs 18.35 pg/ml, pConclusionsThese data suggest that GCSF, which is raised in patient serum, may play an important role in exacerbating disease in ANCA vasculitis. In addition, GCSF therapy for neutropenia should be used with caution in these patients.

Summary OTHER ARTICLES PUBLISHED ON ANCA IN THIS ISSUE How anti-neutrophil cytoplasmic autoantibodies activate neutrophils. Clinical and Experimental Immunology 2012, 169: 220–8. Antibodies against neutrophil proteins myeloperoxidase (MPO) and proteinase 3 are thought to cause disease in anti-neutrophil cytoplasmic antibody (ANCA) vasculitis. There have been a number of recent developments in the animal models of ANCA vasculitis in both mice and rats. These include models based on an immune response to MPO generated in MPO-deficient mice, with other models using MPO-sufficient mice and rats. In addition, there is a report of the use of humanized mice where immunodeficient mice have been engrafted with human haematopoietic stem cells and injected with patient ANCA. Antibodies to another protein lysosomal-associated protein-2 have been found in patients with ANCA vasculitis, and evidence from a rat model suggests that they are also pathogenic. These models all have advantages and disadvantages, which are discussed. We also consider what these models have taught us about the pathogenesis of ANCA vasculitis. Experiments using genetically modified mice and pharmacological inhibition have given insights into disease mechanisms and have identified potential therapeutic targets. Toll-like receptor stimulation modifies disease by acting both at the level of tissue injury and in the generation of the autoimmune response. Complement is also potentially important with data to support the role of the alternative pathway and C5a in particular. Intracellular pathways have been examined, with a role showing p38 mitogen-activated protein kinase and phosphatidylinositol 3-kinase γ. Serine proteases are now known to contribute to disease by release of interleukin-1β in ANCA-activated neutrophils and monocytes. Other potential therapies studied in these models include the use of bortezemib and strategies to modify antibody glycosylation.