Abstract. The role of nephritis-associated antigen as a virulence factor for acute poststreptococcal glomerulonephritis (APSGN) remains to be fully clarified. Nephritis-associated plasmin receptor (NAPlr) was previously isolated from group A streptococcus (GAS) and shown to bind plasmin(ogen). The nucleotide sequence of the naplr gene from GAS isolates obtained from patients with APSGN was determined. The sequence of the putative open reading frame (1011 bp) showed 99.8% identity among isolated strains. Homology screen revealed an exact match with streptococcal glyceraldehyde-3-phosphate dehydrogenase (GAPDH). NAPlr exhibited GAPDH activity in zymography, and it activated the complement pathway in vitro. In APSGN kidney biopsy specimens, NAPlr was observed mainly in the early stage of the disease (1 to 14 d after onset) but was not colocalized with either C3 or IgG as assessed by double immunofluorescence staining. Sera of patients with APSGN, patients with GAS infection without renal involvement, nonrenal pediatric patients, and healthy adults as controls were assayed for antiNAPlr antibody titers. Anti-NAPlr antibodies were present most frequently in APSGN sera, and antibody titers were also significantly higher than in patients with GAS infection alone or in other control patients. Moreover, antibody titers remained elevated during the entire 10-yr follow-up period.

These results indicate that the altered functions of T cells to produce Th2 cytokines and the increased production of IgG4 by B cells in response to these cytokines characterize the immune response in idiopathic membranous nephropathy.

Objective To determine whether a different renal histopathology is associated with the characteristic IgG subclass distribution, and whether a distinct IgG subclass distribution is involved in a unique immunopathological expression, we compared the distributions of glomerular and serum IgG subclasses in diffuse proliferative lupus nephritis (DPLN), membranous LN (MLN), and idiopathic membranous nephropathy (MN).Patients and Methods The glomerular IgG subclass distributions in patients with DPLN(n=7), MLN(n=10) or MN(n=16) were assessed by direct immunofluorescence microscopy. Serum levels of each IgG subclass were quantitated by ELISA in DPLN, MLN, and MN patients, and in normal human sera (NHS) (n=14).Results IgGl, IgG2, IgG3, and, to a lesser degree, IgG4 were similarly present in glomerular deposits in both DPLN and MLN.In contrast, IgG4 was the predominant glomerular IgG subclass in MN. Regarding the serum IgG subclasses, the meanIgG subclass concentrations and the mean proportion of each IgG subclass to the total IgG (%IgG subclass) in DPLNand MLNwere not significantly different from those in NHS,except for the increased %IgGl in MLN.In MN,the mean %IgG4was selectively increased (p<0.01 vs NHS)in association with a slightly elevated IgG4 concentration; however, the meanconcentrations of other IgG subclasses were significantly decreased (p<0.01 vs NHS), and the %IgG subclasses were not significantly different from those in NHS. Conclusions The results indicate that the IgG subclass distribution is not associated with the different renal histopathologies of DPLNand MLN.This study also shows the selective significance of IgG4 in MN,but not in MLN,another form of membranous glomerulopathy. (Internal Medicine 41 : 936-942, 2002)

A nephritogenic antigen for acute poststreptococcal glomerulonephritis (APSGN) was isolated recently from group A streptococcus and termed nephritis-associated plasmin receptor (NAPlr). In vitro experimental data indicate that the pathogenic role of NAPlr occurs through its ability to bind to plasmin and maintain its proteolytic activity. However, the mechanism whereby this antigen induces glomerular damage in vivo has not been fully elucidated. Renal biopsy tissues from 17 patients with APSGN, 8 patients with rapidly progressive glomerulonephritis, and 10 normal kidneys were analyzed in this study. Plasmin-like activity was assessed on cryostat sections by in situ zymography with a plasmin-sensitive synthetic substrate. Serial sections were simultaneously assessed for NAPlr deposition by immunofluorescence staining. Glomerular plasmin-like activity was absent or weak in normal controls and in patients with rapidly progressive glomerulonephritis, although tubulointerstitial activity was occasionally detected. Prominent glomerular plasmin-like activity was found in patients who had APSGN and in whom glomerular NAPlr was positive, whereas it was absent or weak in patients who had APSGN and in whom glomerular NAPlr was negative. The distribution of glomerular plasmin-like activity was identical to that of NAPlr deposition but was generally different from that of fibrin(ogen) deposition as assessed by double staining. The activity was abolished by the addition of aprotinin to the reaction mixture but was not altered by the addition of a matrix metalloprotease inhibitor, a cysteine protease inhibitor, or inhibitors of plasminogen activators. Thus, upregulated glomerular plasmin-like activity in relation to NAPlr deposition in APSGN was identified. This result supports the nephritogenic character of NAPlr and offers insight into the mechanism whereby this antigen induces nephritis.

To investigate a possible role of anti-neutrophil cytoplasmic antibodies directed against myeloperoxidase (MPO-ANCA) in glomerulonephritis, we prepared anti-rat MPO antiserum by immunization of rat MPO into a rabbit. Then we administered anti-rat MPO antiserum (group 1) or normal rabbit serum (NRS) (group 2) into rats before injection of nephrotoxic serum (NTS), which induced nephrotoxic serum nephritis (NTN). Other groups of rats received either anti-rat MPO anti-serum (group 3) or NRS (group 4) before injection of NRS but not NTS. Rats in group 1 and group 2 were sacrificed at either 3 hours, 15 hours, or 14 days after NTS injection. Rats in group 3 and group 4 were sacrificed at 15 hours after the last NRS injection. By light microscopy, in rats with NTN sacrificed at 3 hours, counts of polymorphonuclear leukocytes (PMN) per glomerulus were 21.6 +/- 3.5 in group 1 and 8.4 +/- 1.7 in group 2 (P < 0.01). At 15 hours, massive glomerular fibrin deposits were observed in group 1 rats (fibrin score, 131 +/- 8), but not in group 2 rats (fibrin score, 27 +/- 21; P < 0.01). By direct immunofluorescence microscopy, rat MPO was found along glomerular capillary walls more intensely in group 1 rats than in group 2 rats. No pathological alterations were found in group 3 and group 4 rats. Further, renal elution studies revealed that eluted rabbit IgG contained anti-rat MPO antibodies in group 1 rats but not in group 3 rats. These results suggest that the anti-MPO antibodies are directly involved in the more severe glomerular lesions in group 1 rats via interactions with MPO itself or activation of PMN, which release various kinds of mediators including MPO.