Anti-neutrophil cytoplasmic antibody-associated (ANCA-associated) small vessel necrotizing vasculitis is caused by immune-mediated inflammation of the vessel wall and is diagnosed in some cases by the presence of myeloperoxidase-specific antibodies (MPO-ANCA). This multicenter study sought to determine whether differences in ANCA epitope specificity explain why, in some cases, conventional serologic assays do not correlate with disease activity, why naturally occurring anti-MPO autoantibodies can exist in disease-free individuals, and why ANCA are undetected in patients with ANCA-negative disease. Autoantibodies from human and murine samples were epitope mapped using a highly sensitive epitope excision/mass spectrometry approach. Data indicated that MPO autoantibodies from healthy individuals had epitope specificities different from those present in ANCA disease. Importantly, this methodology led to the discovery of MPO-ANCA in ANCAnegative disease that reacted against a sole linear sequence. Autoantibodies against this epitope had pathogenic properties, as demonstrated by their capacity to activate neutrophils in vitro and to induce nephritis in mice. The confounder for serological detection of these autoantibodies was the presence of a fragment of ceruloplasmin in serum, which was eliminated in purified IgG, allowing detection. These findings implicate immunodominant epitopes in the pathology of ANCA-associated vasculitis and suggest that autoantibody diversity may be common to other autoimmune diseases.

Kim-1, a recently discovered membrane protein, is undetectable in normal kidneys but markedly induced in proximal tubules after ischemic and toxic injury. The function of Kim-1 is unclear, but it is implicated in damage/repair processes. The Kim-1 ectodomain is cleaved by metalloproteinases and detectable in urine. We studied Kim-1 in a nontoxic, nonischemic, model of tubulointerstitial damage caused by acute proteinuria. Uninephrectomized (NX) rats received daily (ip) injections of 2 g BSA (NX+BSA, n = 12) or saline (NX, n = 6) for 3 wk. Kidneys were stained for various damage markers by immunohistochemistry (IHC). Kim-1 mRNA (RT-PCR, in situ hybridization), protein (IHC, Western blotting), and urinary Kim-1 (Luminex) were determined. Spatial relations between Kim-1 and other damage markers were studied by double labeling IHC. NX+BSA rats developed massive proteinuria (1,217 ± 313 vs. 18 ± 2 mg/day in NX, P < 0.001) and significant renal damage. Kim-1 mRNA was upregulated eightfold in NX+BSA (ratio Kim-1/β-actin, 4.08 ± 2.56 vs. 0.52 ± 0.64 in NX, P < 0.001) and localized to damaged tubules. Kim-1 protein expression was markedly induced in NX+BSA (2.46 ± 1.19 vs. 0.39 ± 0.10% staining/field in NX, P < 0.001). Urinary Kim-1 was significantly elevated in NX+BSA (921 ± 592 vs. 87 ± 164 pg/ml in NX, P < 0.001) and correlated with tissue Kim-1 expression ( r = 0.66, P =0.02). Kim-1 protein was found at the apical membrane of dilated nephrons. Kim-1 expression was limited to areas with inflammation (MØ), fibrosis (α-smooth muscle actin), and tubular damage (osteopontin), and only occasionally with tubular dedifferentiation (vimentin). These results implicate involvement of Kim-1 in the pathogenesis of proteinuria-induced renal damage/repair. Urinary Kim-1 levels may serve as a marker of proteinuria-induced renal damage.

Urinary excretion of KIM-1 is an independent predictor of long-term graft loss and therefore a promising new biomarker in early prediction of graft loss.

Kidney injury molecule-1 (KIM-1) is a marker for renal proximal tubular damage, the hallmark of virtually all proteinuric, toxic and ischaemic kidney diseases. KIM-1 has gained increasing interest because of its possible pathophysiological role in modulating tubular damage and repair. In this respect, it is interesting that the best biomarkers often turn out to be important in modulation of damage and some even become therapeutic targets. The emphasis of this review is on structural and biochemical aspects of KIM-1, its expression pattern and its pathophysiological role in renal disease. We also discuss the prognostic impact of KIM-1 in relation to urinary protein excretion. Glomerular (proteinuria) and interstitial markers (KIM-1) might have independent prognostic impact and so may provide independent treatment targets. Finally, the potential of KIM-1 as biomarker of renal damage, as a predictor of renal function decline and its perspectives for monitoring therapy response, are discussed.

Tubulointerstitial lesions are important in the progression of proteinuric renal disease. Tubular kidney injury molecule-1 (Kim-1) is induced in acute renal injury and reversible as a natural course. Kim-1 is also present in chronic renal damage; however, the dynamics of Kim-1 in chronic renal damage and effects of antiproteinuric treatment on Kim-1 are unknown. We studied Kim-1 in adriamycin nephrosis (AN) before and after renin-angiotensin system blockade. A renal biopsy was taken 6 wk after adriamycin injection to study renal damage and Kim-1 expression. Subsequently, ACE inhibition (ACEi; n = 23), angiotensin II antagonist (AT(1A); n = 23), or vehicle (n = 10) was given for 6 wk; healthy rats served as controls (CON; n = 8). In AN, renal Kim-1 mRNA was induced 26-fold vs. CON at week 6, with further increase in vehicle to week 12 (40-fold) but was reduced by ACEi and AT(1A) to 10- and 12-fold vs. CON (P < 0.05 vs. week 6). Kim-1 protein was undetectable in CON; in AN, it was present in brush border of dilated tubules in areas with adjacent interstitial lesions. Renal Kim-1 protein levels increased from weeks 6-12 in vehicle and decreased in ACEi- and AT(1A)-treated groups (P < 0.05). In vehicle, urinary Kim-1 was increased (P < 0.05 vs. CON), with a reduction by ACEi and AT(1A) (P < 0.05 vs. vehicle). Renal and urinary Kim-1 correlated with proteinuria and interstitial damage cross-sectionally. Reductions in proteinuria and renal Kim-1 correlated, which was not associated by corresponding changes in tubulointerstitial fibrosis. In conclusion, on longitudinal follow-up during antiproteinuric treatment increased renal Kim-1 expression is reversible in proportion to proteinuria reduction, likely reflecting reversibility of early tubular injury, supporting its potential as a biomarker for tubulointerstitial processes of damage and repair.

Anti-neutrophil cytoplasmic autoantibodies (ANCA) directed against myeloperoxidase (MPO) and proteinase 3 (Pr3) are considered pathogenic in ANCA-associated necrotizing and crescentic glomerulonephritis (NCGN) and vasculitis. Modulation of ANCA IgG glycosylation may potentially reduce its pathogenicity by abolishing Fc receptor-mediated activation of leukocytes and complement. Here, we investigated whether IgG hydrolysis by the bacterial enzyme endoglycosidase S (EndoS) attenuates ANCA-mediated NCGN. In vitro, treatment of ANCA IgG with EndoS significantly attenuated ANCAmediated neutrophil activation without affecting antigen-binding capacity. In a mouse model of anti-MPO IgG/LPS-induced NCGN, we induced disease with either unmodified or EndoS-treated (deglycosylated) anti-MPO IgG. In separate experiments, we administered EndoS systemically after disease induction with unmodified anti-MPO IgG. Pretreatment of anti-MPO IgG with EndoS reduced hematuria, leukocyturia, and albuminuria and attenuated both neutrophil influx and formation of glomerular crescents. After inducing disease with unmodified anti-MPO IgG, systemic treatment with EndoS reduced albuminuria and glomerular crescent formation when initiated after 3 but not 24 hours. In conclusion, IgG glycan hydrolysis by EndoS attenuates ANCA-induced neutrophil activation in vitro and prevents induction of anti-MPO IgG/LPS-mediated NCGN in vivo. Systemic treatment with EndoS early after disease induction attenuates the development of disease. Thus, modulation of IgG glycosylation is a promising strategy to interfere with ANCA-mediated inflammatory processes.

Although many observations suggest a link between infections and the development of vasculitis, no direct proof exists. Transcriptomic and proteomic studies of the pathogens involved could aid in identifying specific or common traits of pathogens that are relevant for the development and reactivation of vasculitis.

de Borst MH, van Timmeren MM, Vaidya VS, de Boer RA, van Dalen MB, Kramer AB, Schuurs TA, Bonventre JV, Navis G, van Goor H. Induction of kidney injury molecule-1 in homozygous Ren2 rats is attenuated by blockade of the renin-angiotensin system or p38 MAP kinase. Am J Physiol Renal Physiol 292: F313-F320, 2007. First published August 8, 2006; doi:10.1152/ajprenal.00180.2006.-Kidney injury molecule-1 (Kim-1) is associated with ischemic and proteinuric tubular injury; however, whether dysregulation of the reninangiotensin system (RAS) can also induce Kim-1 is unknown. We studied Kim-1 expression in homozygous Ren2 rats, characterized by renal damage through excessive RAS activation. We also investigated whether antifibrotic treatment (RAS blockade or p38 MAP kinase inhibition) would affect Kim-1 expression. At 7 wk of age, homozygous Ren2 rats received a nonhypotensive dose of candesartan (0.05 mg ⅐ kg Ϫ1 ⅐ day Ϫ1 sc) or the p38 inhibitor SB-239063 (15 mg ⅐ kg Ϫ1 ⅐ day Ϫ1 sc) for 4 wk; untreated Ren2 and Sprague-Dawley (SD) rats served as controls. Kim-1 mRNA and protein expression were determined by quantitative PCR and immunohistochemistry, respectively, and related to markers of prefibrotic renal damage. Urinary Kim-1 was measured in 8-wk-old Ren2 and SD rats with and without angiotensinconverting enzyme inhibition (ramipril, 1 mg ⅐ kg Ϫ1 ⅐ day Ϫ1 in drinking water for 4 wk). Untreated Ren2 rats showed a Ͼ20-fold increase in renal Kim-1 mRNA (expressed as Kim-1-to-GAPDH ratio): 75.5 Ϯ 43.6 vs. 3.1 Ϯ 1.0 in SD rats (P Ͻ 0.01). Candesartan and SB-239063 strongly reduced Kim-1 mRNA: 3.1 Ϯ 1.5 (P Ͻ 0.01) and 9.8 Ϯ 4.2 (P Ͻ 0.05), respectively. Kim-1 protein expression in damaged tubules paralleled mRNA expression. Kim-1 expression correlated with renal osteopontin, ␣-smooth muscle actin, and collagen III expression and with tubulointerstitial fibrosis. Damaged tubular segments expressing activated p38 also expressed Kim-1. Urinary Kim-1 was increased in Ren2 vs. SD (458 Ϯ 70 vs. 27 Ϯ 2 pg/ml, P Ͻ 0.01) rats and abolished in Ren2 rats treated with ramipril (33 Ϯ 5 pg/ml, P Ͻ 0.01). Kim-1 is associated with development of RAS-mediated renal damage. Antifibrotic treatment through RAS blockade or p38 MAP kinase inhibition reduced Kim-1 in the homozygous Ren2 model. homozygous TGR(mRen2)27; angiotensin II type 1 receptor THE RENIN-ANGIOTENSIN SYSTEM (RAS) is pivotal in mammalian physiology; however, disturbance of the RAS is one of the major pathways involved in the initiation and progression of renal disease. Chronic RAS dysregulation may result in glomerular and tubulointerstitial pathophysiology through direct effects of angiotensin II (ANG II), via the ANG II type 1 (AT 1 ) receptor, and downstream through activation of mitogen-activated protein (MAP) kinases and transcription factors (3,12,17). Interventions that inhibit activity of the RAS [e.g., angiotensin-converting enzyme (ACE) inhibition or AT 1 receptor blockade] are renoprotective and may slow or even halt the progression of chronic nephropathies (16).Vario...