Mutsuko Hidaka

Glomerular Deposition and Urinary Excretion of Complement Factor H in Idiopathic Membranous Nephropathy

Background/Aims: The complement system plays an important role in the pathogenesis of membranous nephropathy (MN). In order to elucidate the regulatory mechanism of complement activation, we demonstrated glomerular deposition and urinary excretion of complement factor H, which controls the alternative pathway and the amplification loop at the C3 step, in patients with idiopathic MN. Methods: Renal biopsy specimens from 20 patients with idiopathic MN were studied immunohistochemically using monoclonal antibodies against complement components including factor H. SDS-PAGE and Western blotting analysis of urine samples were performed, and the urinary excretion of factor H and C5b-9 were measured by quantitative sandwich ELISA. Results: Intense glomerular deposition of factor H was observed with C3b·C3c and C5b-9 at an early stage of the disease. Factor H was detected in Western blots of urine samples, but factor H-like protein 1 (FHL-1) was not. The mean level of urinary factor H was elevated (86.30 ± 21.93 U/mg urinary creatinine) in comparison to that of normal controls (4.76 ± 1.03 U/mg urinary creatinine). Urinary factor H level exhibited no correlation with clinical parameters; however, a negative correlation was found between urinary C5b-9/factor H and creatinine clearance (r = 0.662, p < 0.01). Conclusion: The source of glomerular and urinary factor H is supposedly a 150-kD protein. There was no evidence to suggest that FHL-1 is synthesized at the site of inflammation. The urinary C5b-9 to urinary factor H ratio is indicative of the degree of ongoing complement activation in the glomeruli and complement-mediated renal injury. These findings suggest that factor H contributes to the control mechanism of in situ complement activation and prevents renal damage in idiopathic MN.

Inhibitory effect of free sialic acid on complement activation and its significance in hypocomplementemic glomerulonephritis.

The role of free sialic acid on complement activation was investigated. The serum levels of free sialic acid and total sialic acid were measured by previously described methods in 16 patients with acute post‐infectious glomerulonephritis (AGN), 27 patients with systemic lupus erythematosus (SLE), 15 patients with persistent hypocomplementemic membranoproliferative glomerulonephritis (MPGN), and 13 healthy controls. A statistical study demonstrated an increased level of free sialic acid in patients with AGN and SLE in which the hypocomplementemia improved throughout the course and a decreased level of free sialic acid in patients with MPGN and SLE in which hypocomplementemia continued throughout the course. The levels of total sialic acid were significantly increased in patients with AGN and SLE and were significantly decreased in patients with MPGN. There was no correlation between the levels of free sialic acid and total sialic acid in patients with AGN, in whom the levels of both total and free sialic acids were increased. To examine the effect of free sialic acid on the complement cascade, lipopolysaccharide (LPS) was incubated with normal human serum (NHS) in the various concentrations of N‐acetyl neuraminic acid (NANA), a member of the sialic acid group. The incubation mixtures were examined by enzyme immunoassay using monoclonal anti‐iC3b antibody or anti‐Bb antibody. Native C3 or Factor B in NHS broke down less following the addition of NANA. To elucidate the role of NANA on the hemolytic function of C3, a rabbit erythrocyte (Ra E) hemolytic assay was carried out. Ra E lysed completely in the presence of R3 with native C3. However, hemolysis occurred to a lesser degree in C3‐depleted serum (R3) or R3 with NANA‐treated C3. To investigate the influence of NANA on complement components, the levels of complement components were measured in the incubation mixture with various doses of NANA and NHS. The levels of C3 and C5 were significantly decreased after the addition of NANA, even though the levels of Factor H and Factor I were not markedly changed. These data indicate that NANA exerts an influence on the complement components even though it has no effect on the regulatory proteins of complement. Our in vitro findings, together with the in vivo data, suggest that free sialic acid might have an inhibitory effect on the activation of C3 and the following complement cascade, and might also have been responsible for the improvement of hypocomplementemia. J. Clin. Lab. Anal. 13:173–179, 1999.

A case of renal involvement in persistent immune activation caused by chlamydial salpingitis.

Abstract. A 24-year-old woman presented with renal insufficiency, macrohematuria, and mild urinary protein. Polyclonal hypergamma-globulinemia, thrombocytosis, increased concentration of serum, and urinary interleukin (IL)-6 all indicated persistent immune activation caused by a Chlamydia trachomatis infection of the fallopian tube. Gynecological treatment with levofloxacin was effective both for the renal symptoms and other immunological parameters. First and second renal biopsy specimens showed an immune-complex glomerulopathy with extensive interstitial infiltration of many types of inflammatory cells, including plasma cells. Thus, we conclude that chlamydial salpingitis must be considered as one causative disease factor for renal involvement by means of its persistent immune activation effects.

Complement activation via lectin pathway in IgA nephropathy

Although previous reports suggest the importance of complement system on glomerular injury in IgA nephropathy (IgAN), the mechanism of complement activation is not clear. Recently, the third route of complement activation, the lectin pathway, has been shown. In the lectin pathway, mannose-binding lectin (MBL) bound to mannose or N-acetylglucosamine terminated ligands activates complement cascade independent of antibody using MBL-associated serine proteases (MASP-1 and MASP-2). The purpose of this study was to determine whether the lectin pathway was involved in the pathogenetic mechanism of IgAN. Renal biopsy material from patients with IgAN was studied using an immunohistochemical method, and a clinicopathological correlation was examined. The results were as follows: 1. Glomerular deposition of MBL, which was accompanied by MASP-1, was detected in 11 of 45 (24.4%) cases with IgAN. 2. The deposited MBL/MASP-1 was observed to associate with C3b/C3c and C5b-9 but not with IgG, IgM, C1q, C4c, or properdin. 3. Compared with MBL/MASP-1 negative cases of IgAN, the positive cases were young and the renal biopsies had been performed at an early stage of the disease. 4. No significant correlation was found between glomerualr deposition of MBL/MASP-1 and proteinuria, hematuria, creatinine clearance, and serum levels of IgA, C3, or C4 at the time of renal biopsy. 5. There was no significant difference between MBL/ MASP-1 positive cases and MBL/MASP-1 negative cases in plasma levels of circulating immune complexes, soluble C5b-9, C4d, or Bb. 6. Glomerular deposition of C4-binding protein, which played a regulatory role in the lectin pathway, was detected in all of MBL/MASP-1 positive cases, although the plasma levels were not significantly different between the positive and the negative cases.