systemic lupus erythematosus ( sle ) is a chronic autoimmune disease characterized by complex clinical manifestation and chronic inflammatory processes involving autoimmunity against multiple systems and multiple organs . lupus nephritis ( ln ) , the appearance of a disservice caused by sle to kidney , contributes to high mortality . as active stage and rest stage alternate iteratively in ln disease process , observation to sle activity , especially to the level of renal activity , is extremely important to therapeutic regimen decisions and treatment modifications as well as prognosis . at present , activity of sle is assessed based on clinical symptoms and biochemistry parameters such as autoantibody ( e.g. , anti - dsdna ) and serum complement renal biopsy has been the gold standard for assessment of kidney damage and disease activity , but its invasive feature has restricted its use . recently there has been a surge of interest in defining novel ln biomarkers to evaluate disease activity [ 1 , 2 ] . over the last few years , evidences showed that tumor necrosis factor - like weak inducer of apoptosis ( tweak ) was expressed in a high level in the kidney of ln animal model . this study approached to the relationship between urinary tweak level and the activity of ln in the asian patients in china . forty - six cases of patients with ln ( 12 of nonactive ln and 34 of active ln ) were selected from patients hospitalized in the second xiangya hospital from october 2008 to march 2009 . of those 34 cases have routine renal biopsy . the patients aged 14  ~  53 years with a mean duration of disease for 10.47  4.12 months . every case meets at least 4 items of sle diagnostic criteria revised by american rheumatism association in 1982 . all the patients received no treatment of immunosuppressive agent such as methylprednisolone ( mp ) , cyclophosphamide ( ctx ) , mycophenolate ( mmf ) , ciclosporin a ( csa ) , or tacrolimus ( fk506 ) for 3 months prior to the diagnoses of ln by renal biopsy . occasional use of hydroprednisone in some patients was subjected to short time and low doses ( < 30  mg / d ) . biopsy specimens were fixed , sectioning and staining ( including he , pas , pasm , and masson ) , then observed under light microscopy . 10  ml urina sanguinis from each patient was centrifuged . then clear supernatant liquid was used for tweak and mcp-1 detection .   for renal involvement , renal sle disease activity index ( sledai ) the score consists of the four kidney - related parameters : hematuria , pyuria , proteinuria , and urinary casts . scores for the renal sledai can range from 0 ( inactive renal disease ) to a maximum of 16 . a sledai score of 4 was taken as an indicator of active lupus nephritis . according to the 2000 sledai scores nonactive group : 12 cases ( 3 males and 9 females ) , ln duration of 14.06  4.55 months ; active group : 34 cases ( 1 male and 33 females ) , ln duration of 8.44  2.13 months . renal biopsy specimens from ln patients were classified according to the world health organization ( who ) criteria : minimal changes ( class i ) , mesangial alterations ( class ii ) , focal proliferative ( class iii ) , diffuse proliferative ( class iv ) , and membranous ( class v ) glomerulonephritis . we made semiquantitative score for each renal biopsy specimen according to 2000 hill 's biopsy index scoring criteria for lupus nephritis . activity index contained glomerular activity index ( gai ) and tubulointerstitial activity index ( tiai ) . components of glomerular activity index : ( 1 ) glomerular proliferation ; ( 2 ) polymorphonuclear leukocytes ; ( 3 ) karyorrhexis / fibrinoid necrosis ; ( 4 ) cellular crescents ; ( 5 ) hyaline deposits ; ( 6 ) glomerular monocytes . components of tubulointerstitial activity index : ( 1 ) tubular cell pyknosis ; ( 2 ) tubular nuclear  activation  ; ( 3 ) tubular cell necrosis ; ( 4 ) tubular cell flattening ; ( 5 ) macrophages in tubular lumens ; ( 6 ) epithelial cells in tubular lumens ; ( 7 ) interstitial inflammation . components of chronicity index : ( 1 ) glomerulosclerosis ; ( 2 ) glomerular scar ; ( 3 ) fibrous crescentic ; ( 4 ) tubular atrophy ; ( 5 ) interstitial fibrosis . urinary tweak levels and urinary mcp-1 levels were measured by human tweak elisa kits and human mcp-1 elisa kits from xin bo sheng bio - technology co. , ltd . we measured absorbance a values by microplate reader at 450  nm wavelength and then calculated urinary tweak concentrations and urinary mcp-1 concentrations according to the standard curve . urinary tweak levels and urinary mcp-1 levels were normalized to urinary creatinine concentrations measured in the same spot urine , expressed as pg / mg creatinine . measurement data consistent with normal distribution was expressed as   s. lsd - t test was used for comparing two groups . spearman 's analysis was used for correlations between quantitative data and semiquantitative data or between two semiquantitative data . p - value < 0.05 was considered statistically different and p - value < 0.01 as statistically significant . sle patients ( n = 46 ) were recruited into two groups : sle patients with active lupus nephritis ( active group ) and those patients with inactive or nonrenal involvement ( nonactive group ) . statistically , significant differences were found between both groups in the following variables : red blood cell count in urine ( /hp ) , 24  h urinary proteins ( g/24  h ) , serum bun ( mmol / l ) , serum creatinine level ( mol / l ) , c3 ( mmol / l ) , and c4 ( mmol / l ) . the pathological changes of active lupus nephritis contain glomerular mesangial cells proliferation , cellular crescents , thickening of capillary walls , karyorrhexis , hyaline thrombi , and interstitial inflammatory infiltration ( figure 1 ) . to determine whether tweak correlates with ln activity , we compared urinary tweak levels of ln active group with nonactive group . urinary mcp-1 levels were used for positive control . as presented in figure 2 , urinary tweak levels of ln active group were significantly higher than those of nonactive group ( 10.29  1.81  pg / mgcr versus 2.14  0.30  pg / mgcr , p < 0.01 ) . urinary mcp-1 levels ( umcp-1 ) of ln active group were also significantly higher than those of nonactive group ( 103.60  15.79  pg / mgcr versus 20.19  2.93  pg / mgcr , p < 0.01 ) . the urinary tweak levels of patients with ln had significantly positive correlation ( r = 0.825 , p < 0.01 ) with active index ( ai ) ( p < 0.01 ) , including glomerular activity index ( gai ) ( rgai = 0.745 , rtiai = 0.751 ) and those with tubulointerstitial activity index ( tiai ) , but had no significant correlation ( p > 0.05 ) with chronicity index ( ci ) ( figure 3 ) . monocyte chemoattractant protein-1 ( mcp-1 ) has been presumed a biomarker to monitor ln activity , proved by evidences of biochemistry and immunology . results showed that the urinary mcp-1 levels of patients with ln had significantly positive correlation ( r = 0.800 , p < 0.01 ) with active index ( ai ) , including glomerular activity index ( gai ) , and those with tubulointerstitial activity index ( tiai ) ( rgai = 0.804 , rtiai = 0.769 ) but had no significant correlation ( p > 0.05 ) with chronicity index ( ci ) ( figure 4 ) . our analysis showed that the urinary tweak levels in active group had significantly positive correlation ( r = 0.809 , p < 0.01 ) with urinary mcp-1 levels , while nonactive group 's urinary tweak levels had no correlation with the urinary levels of mcp-1 ( p > 0.05 ) ( figure 5 ) . , several studies have found that a disorder of the regulation of apoptosis is an important factor in sle progress , such as tweak . tweak combined with its receptor fn14 could activate i-b kinase ( ikk ) , resulting in the degradation and activation of i-b . i-b transferred to cell nucleus and increased mcp-1 , rantes , and il-6 expression , causing inflammatory cell infiltration . researches also reported that tweak / fn14 induced apoptosis of glomerular mesangial cells and tubular epithelial cells with induction of proinflammatory cytokines , thereby causing glomerular and tubular injury , which might play an important role in the pathogenesis of lupus nephritis [ 7 , 8 ] . in this study , we analyzed the relationship between tweak and the renal activity of lupus in order to prove tweak as a marker of lupus nephritis . previous studies have shown that serum tweak levels are significantly lower in sle patients than in healthy individuals [ 9 , 10 ] . a cross - sectional study by gladman et al .   in the ohio sle research center and the albers albert einstein medical college showed that patients with lupus nephritis had significantly higher urinary tweak levels than those without kidney injury , and the patients in active stage of lupus , with kidney injury or not , had higher urinary tweak levels than those in nonactive stage , indicating that an elevated level of urinary tweak may suggest active lupus nephritis . in our study , active ln patients had significantly higher urinary tweak levels , compared to those in chronic , stable condition . and our study provides a supporting result to the conclusion by schwartz et al . in chinese patients , indicating that tweak also played an important role in the active lupus nephritis in asian cases . in this study , results also showed that urinary tweak levels had significantly correlated with ln renal pathology ai containing gai and tiai . this indicates that urinary tweak levels could reflect the level of activity in ln patients . in addition , the expression of tweak is relevant to glomerular lesions and tubulointerstitial lesions . the elevation of urinary tweak level may be related to the increased expression of tweak in kidney . however , it is still uncertain whether kidney is the only organ expressing tweak , which is needed to be confirmed in the future . we also found that urinary tweak levels have no difference between class ii , iii , and iv of ln among 31 patients ( result is not showed in this article ) , indicating that urinary tweak detection can not replace renal biopsy entirely in diagnostic process . mcp-1 was proved to be a biomarker of lupus nephritis disease activity [ 12 , 13 ] . in vivo , urinary mcp-1 has positive correlation with the increase in urine n - acetyl--d - glucosaminidase ( nag ) and urine protein in 24  h . a significantly positive correlation between mcp-1 and ai has been showed in our study ( figure 4 ) . in addition , urinary tweak levels have significantly positive correlation with active ln ( r = 0.809 , p < 0.01 ) and urinary levels of mcp-1 , pointing to the potential of urinary tweak as a disease - monitoring biomarker . the injured mononuclear cells released nuclear self - antigens by increasing mcp-1 expression , and the clearance of apoptotic debris reduced relatively , which might be one of the mechanisms for the development of lupus . researches indicated that tweak combined with fn14 induced mcp-1 in renal tubular epithelial cells , causing rela subunit of nf-b transferring from cytoplasm to nucleus , leading to the activation of target gene which encodes mcp-1 [ 6 , 15 , 16 ] . these results proved that tweak is one of the upstream regulatory factors of mcp-1 in inflammatory process . in conclusion , urinary tweak levels of patients with active ln significantly positively correlated with urinary levels of mcp-1 , indicating the potential disease - monitoring biomarker of urinary tweak .
objective . 
 this study is designed to observe the urinary tumor necrosis factor - like weak inducer of apoptosis ( tweak ) levels in patients with lupus nephritis ( ln ) and to identify new biomarker of lupus nephritis activity . 
 methods . 
 study subjects were 46 cases of patients with ln ( including 34 of active cases ) who underwent routine renal biopsy . 
 activity and chronicity indexes of ln were assessed using pathological criteria proposed by hill et al . in 2000 . 
 urinary tweak ( utweak ) level and monocyte chemoattractant protein-1 ( mcp-1 ) level were detected by elisa . 
 results . 
 urinary tweak level was significantly higher in active ln group than in non - active ln group . 
 correlation analysis showed that urinary tweak levels were significantly correlated with activity index ( r = 0.825 , p < 0.01 ) , glomerular activity index ( r = 0.754 , p < 0.01 ) , and tubulointerstitial qualitative activity index ( r = 0.751 , p < 0.01 ) , while not significant correlated with chronicity index ( p > 0.05 ) . 
 the association between urinary tweak levels and urinary mcp-1 levels were significant in active ln group ( r = 0.809 , p < 0.01 ) but not significant in non - active ln group ( p > 0.05 ) . 
 conclusions . 
 uweak levels were correlated with all active indexes of ln , suggesting its potential role as novel biomarker of active lupus nephritis .