Complement activation products in the circulation and urine of primary membranous nephropathy.

BACKGROUND: Complement activation plays a substantial role in the pathogenesis of primary membranous nephropathy (pMN). C5b-9, C3c, MBL, and factor B have been documented in the subepithelial immune deposits. However, the changing of complement activation products in circulation and urine is not clear. METHODS: We measured the circulating and urinary levels of C1q, MBL, C4d, Bb, properdin, C3a, C5a, and sC5b-9, in 134 patients with biopsy-proven pMN, by enzyme-linked immunosorbent assay. All the plasma values were corrected by eGFR and all the urinary values were corrected by urinary creatinine and urinary protein excretion. Anti-PLA2R antibodies were measured in all patients. RESULTS: The plasma complement activation products were elevated both in the patients with and without anti-PLA2R antibodies. C3a levels were remarkably increased in the circulation and urine, much higher than the elevated levels of C5a. C5b-9 was in normal range in plasma, but significantly higher in urine. The urinary C5a had a positive correlation with anti-PLA2R antibody levels and urinary protein. The plasma level of C4d was elevated, but C1q and MBL were comparable to healthy controls. Positive correlations were observed between plasma C4d/MBL and urinary protein, only in the patients with positive anti-PLA2R antibodies but not in those without. The plasma level of Bb was elevated and had positive correlation with urinary protein only in the patients without anti-PLA2R antibodies. CONCLUSION: Complement activation products were remarkable increased in pMN and may serve as sensitive biomarkers of disease activity. The complement may be activated through lectin pathway with the existence of anti-PLA2R antibodies, while through alternative pathway in the absence of antibody.

Urine complement activation fragments are increased in patients with kidney injury after cardiac surgery.

Experiments in mouse models have shown that the complement cascade is activated within the kidney after ischemia-reperfusion and that complement activation contributes to tubular injury in this setting. Less is known, however, about complement activation in human kidneys after ischemia or whether complement activation in the tubulointerstitium can be detected by measurement of complement fragments in the urine. We hypothesized that urine biomarkers of complement activation would rapidly increase in patients who develop ischemic acute kidney injury, signaling complement activation within the kidney. We confirmed that the alternative pathway of complement is activated in the kidneys of mice after ischemia-reperfusion, and we found that levels of factor B fragments (generated during alternative pathway activation) rapidly increase in the urine. We next performed a case-control study in which we measured complement fragments in human urine samples from patients undergoing cardiac surgery using ELISAs. The level of Ba increased after cardiac surgery and was significantly higher in patients who developed acute kidney injury. The increase in Ba also correlated with magnitude of the subsequent rise in serum creatinine and with the need for hemodialysis during the hospitalization. These findings demonstrate that the alternative pathway of complement is activated in patients who develop acute kidney injury after cardiac surgery and that increases in the level of urine Ba may be a predictive and functional biomarker of severe kidney injury.

Alternative complement pathway activation products in urine and kidneys of patients with ANCA-associated GN.

BACKGROUND AND OBJECTIVES: Previous study revealed that complement activation products of the alternative pathway could be detected in renal specimens of human ANCA-associated vasculitis. The current study aimed to investigate the clinical and pathologic significance of complement activation products in the urine and kidneys of patients with ANCA-associated vasculitis. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Renal biopsy specimens from 29 patients with ANCA-associated vasculitis diagnosed at Peking University First Hospital from January of 2008 to December of 2010 were randomly collected. Urine samples from 27 of 29 patients in active stage and 22 ANCA-associated vasculitis patients in complete remission who were independent of the above-mentioned 29 patients were collected. Urine samples from 28 patients with lupus nephritis and 25 healthy individuals were also collected. The renal deposition of Bb, C3d, and C5b-9 were detected by immunohistochemistry. The urinary levels of Bb, C3a, C5a, and soluble C5b-9 were determined by ELISA. RESULTS: The deposition, measured by the mean optical density of Bb, which is an alternative complement pathway marker, in glomeruli correlated with the proportion of total crescents (r=0.50, P=0.006), the extent of interstitial infiltrate (r=0.59, P=0.001), interstitial fibrosis (r=0.45, P=0.01), and tubular atrophy (r=0.55, P=0.002), whereas it correlated inversely with the proportion of normal glomeruli (r=-0.49, P=0.008). The urinary levels of Bb, C3a, C5a, and soluble C5b-9 were all significantly higher in active compared with remission stage. The urinary levels of Bb in patients with active ANCA-associated vasculitis correlated with the serum creatinine (r=0.56, P=0.002) and correlated inversely with the proportion of normal glomeruli in renal specimens (r=-0.49, P=0.009). CONCLUSIONS: The present study provides additional evidence that complement activation through the alternative pathway occurred in the development of ANCA-associated vasculitis. The renal deposition of Bb and urinary Bb levels were associated with the severity of renal injury.

The role of I and B in peritonitis associated with the nephrotic syndrome of childhood.

Children with nephrotic syndrome (NS) are susceptible to bacterial infections, including primary bacterial peritonitis. Immunologic abnormalities associated with NS include low serum levels of the complement proteins I and B of the alternative complement pathway. We developed a novel and highly sensitive enzyme immunoassay using murine MAb to I and B to quantitate urinary concentrations of these proteins. We studied 22 patients with minimal change NS, including seven with a history of peritonitis (1.6 +/- 0.3 episodes, mean +/- SEM) and 15 without such a history. The two groups did not differ significantly in age, sex, race, age at onset of disease, or duration of disease. Children with minimal change NS complicated by peritonitis had 1) increased urinary excretion of both I (p < 0.05) and B (p < 0.05) in relapse versus remission, 2) greater excretion of I in both relapse (p < 0.01) and remission (p < 0.05) compared with patients without peritonitis, 3) greater excretion of B in relapse compared with patients without peritonitis (p < 0.05), and 4) decreased plasma levels of I compared with patients without peritonitis and controls (p < 0.01) and decreased plasma levels of B compared with controls. Increased urinary excretion of I correlated with decreased plasma levels of I (r = 0.88, p < 0.001). These data support our initial hypothesis that depressed plasma concentrations of these proteins of the alternative complement pathway may predispose patients with minimal change NS to peritonitis and that urinary loss of these proteins is a tenable mechanism.

The complements and immunoglobulins in different media of healthy pregnant women and in pregnant women with increased blood pressure.

We have determined the levels of complement C3, C4 and immunoglobulin G, M, A in mothers' and cord blood serum. Parallelly properdin factor B and immunoglobulin G tests were done in urine samples. All estimations were performed on Immunochemistry Analyzer "Beckman". The investigations were made on 30 healthy pregnant women and 30 with arterial hypertension at the end of third trimester. In the mothers' serum C3 was not significantly changed. In the cord blood of healthy pregnant women it was 0.69 g/L. (SD 0.12) and in those with hypertension 0.38 g/L. (SD 0.15), which means significantly decreased. Complements C4 was not significantly increased in mothers' and cord blood serum. Properdin factor B was significantly increased in mothers' and cord blood serum (healthy pregnant women in serum 0.38 g/L., SD 0.07; with hypertension 0.48 g/L., SD 0.15; while in the cord blood serum of healthy women it was 0.14 g/L., SD 0.06; and hypertensive it was 0.22 g/L., SD 0.10). The same parameter was significantly decreased in the urine of healthy subjects 3.94 mg/L., SD 1.91; and in the hypertensive too, 2.42 mg/L., SD 0.90. The IgG level was significantly increased in the urine of healthy pregnant women 4.42 mg/L., SD 2.24; with hypertension 6.64 mg/L., SD 3.61. IgM was not significantly changed in mothers' and cord blood serum. IgA was significantly increased in the cord blood serum of healthy mothers', 0.02 g/L., SD 0.01, with hypertension 0.12 g/L., SD 0.05.