The role of nephritis-associated plasmin receptor (NAPlr) in glomerulonephritis associated with streptococcal infection

Parvovirus B19-related membranoproliferative glomerulonephritis presenting with positive glomerular staining for nephritis-associated plasmin receptor: a case report and review of the literature

Several cases of glomerulonephritis occurring after infection with human parvovirus B19 (PVB19) have been reported. However, the pathogenesis and clinicopathological features of PVB19-related glomerulonephritis remain elusive. We describe the case of a 34 year-old woman who showed nephrotic syndrome and microscopic hematuria 10 days after PVB19 infection. Blood pressure and renal function were within normal ranges. Laboratory tests showed positive results for anti-PVB19 immunoglobulin (Ig)M antibody and complement 3 (C3) hypocomplementemia. Antibody to streptolysin O (ASO) was slightly elevated, but bacterial cultures yielded no colonies. Light microscopy of renal biopsy was compatible with membranoproliferative glomerulonephritis (MPGN). Immunofluorescence microscopy showed intense staining for C3 and faint staining for IgG on the glomerular capillary wall and paramesangial area. Electron micrography showed subendothelial electron-dense deposits (EDDs), but hump-shaped subepithelial EDDs were not evident. PBV19-DNA was absent from renal tissue. Moreover, glomeruli showed positive staining for nephritis-associated plasmin receptor (NAPlr) and plasmin activity with similar distribution. Around 6 months after PVB19 infection, levels of anti-PVB19 IgM antibody spontaneously tuned negative with an apparent reduction of proteinuria and improvement of hypocomplementemia, although ASO level remained unchanged. This appears to represent the first description of positive glomerular staining for NAPlr in MPGN after PVB19 infection. Based on a review of 27 cases, including our own case, the MPGN lesions could be attributable to PVB19 infection. Clinicopathological features of this case were incompatible with post-streptococcal acute glomerulonephritis. We presume that a PBV19-derived glomerular pathogen that cross-reacts with anti-NAPlr antibody might be involved in the development of PVB19-related MPGN.

Angiotensin II and post-streptococcal glomerulonephritis

BACKGROUND

Post-streptococcal glomerulonephritis (PSGN) is a consequence of the infection by group A beta-hemolytic streptococcus. During this infection, various immunological processes generated by streptococcal antigens are triggered, such as the induction of antibodies and immune complexes. This activation of the immune system involves both innate and acquired immunity. The immunological events that occur at the renal level lead to kidney damage with chronic renal failure as well as resolution of the pathological process (in most cases). Angiotensin II (Ang II) is a molecule with vasopressor and pro-inflammatory capacities, being an important factor in various inflammatory processes. During PSGN some events are defined that make Ang II conceivable as a molecule involved in the inflammatory processes during the disease.

CONCLUSION

This review is focused on defining which reported events would be related to the presence of this hormone in PSGN.

Streptococcal infection and autoimmune diseases

Excessive activation of immune cells by environmental factors, such as infection or individual genetic risk, causes various autoimmune diseases. Streptococcus species are gram-positive bacteria that colonize the nasopharynx, respiratory tract, gastrointestinal tract, genitourinary tract, and skin. Group A Streptococcus (GAS) species cause various symptoms, ranging from mild infections, such as tonsillitis and pharyngitis, to serious infections, such as necrotizing fasciitis and streptococcal toxic shock syndrome. The contribution of GAS infections to several autoimmune diseases, including acute rheumatic fever, vasculitis, and neuropsychiatric disorders, has been studied. In this review, we focus on the association between streptococcal infections and autoimmune diseases, and discuss current research on the mechanisms underlying the initiation and progression of autoimmune diseases.

Mechanisms that potentially contribute to the development of post-streptococcal glomerulonephritis

Post-streptococcal glomerulonephritis (PSGN) is primarily associated with preceding group A streptococcal skin or throat infections, now mainly observed in economically disadvantaged communities. This condition significantly predisposes individuals to later-life chronic kidney disease and concurrent renal complications, with the elderly experiencing increased severity and less favourable outcomes. Streptococcal pyrogenic exotoxin B and nephritis-associated plasmin receptor are identified nephritogenic antigens (nephritogens). Pathogenesis of PSGN is multifactorial. It can involve the formation of antigen-antibody immune complexes, causing inflammatory damage to renal glomeruli. Deposition of circulating immune complexes or in situ formation of immune complexes in glomeruli, or both, results in glomerulonephritis. Additionally, molecular mimicry is hypothesized as a mechanism, wherein cross-reactivity between anti-streptococcal antibodies and glomerular intrinsic matrix proteins leads to glomerulonephritis. Besides, as observed in clinical studies, streptococcal inhibitor of complement, a streptococcal-secreted protein, can also be associated with PSGN. However, the interplay between these streptococcal antigens in the pathogenesis of PSGN necessitates further investigation. Despite the clinical significance of PSGN, the lack of credible animal models poses challenges in understanding the association between streptococcal antigens and the disease process. This review outlines the postulated mechanisms implicated in the development of PSGN with possible therapeutic approaches.

The Role of the Complement System in the Pathogenesis of Infectious Forms of Hemolytic Uremic Syndrome

Hemolytic uremic syndrome (HUS) is an acute disease and the most common cause of childhood acute renal failure. HUS is characterized by a triad of symptoms: microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. In most of the cases, HUS occurs as a result of infection caused by Shiga toxin-producing microbes: hemorrhagic Escherichia coli and Shigella dysenteriae type 1. They account for up to 90% of all cases of HUS. The remaining 10% of cases grouped under the general term atypical HUS represent a heterogeneous group of diseases with similar clinical signs. Emerging evidence suggests that in addition to E. coli and S. dysenteriae type 1, a variety of bacterial and viral infections can cause the development of HUS. In particular, infectious diseases act as the main cause of aHUS recurrence. The pathogenesis of most cases of atypical HUS is based on congenital or acquired defects of complement system. This review presents summarized data from recent studies, suggesting that complement dysregulation is a key pathogenetic factor in various types of infection-induced HUS. Separate links in the complement system are considered, the damage of which during bacterial and viral infections can lead to complement hyperactivation following by microvascular endothelial injury and development of acute renal failure.

IgA-dominant infection-related glomerulonephritis with NAPlr-positive tubulointerstitial nephritis

Infection-related glomerulonephritis (IRGN) is one of the most common causes of acute kidney injury (AKI). Positive glomerular staining of the nephritis-associated plasmin receptor (NAPlr) has been reported as a useful biomarker of IRGN. Although the infection can provoke acute tubulointerstitial nephritis (AIN), there are few reports of positive staining for NAPlr with AIN. We report a case of methicillin-sensitive Staphylococcus aureus (MSSA) infection-related nephritis complicated with AIN, which showed positive staining for tubulointerstitial NAPlr. The patient developed AKI and nephrotic syndrome during an intraperitoneal MSSA infection. A diagnosis of IRGN complicated by infection-related acute tubulointerstitial nephritis (IRAIN) was made based on glomerular endocapillary proliferation with tubulointerstitial infiltrating cells and tubular atrophy. Tubulointerstitial infiltrating cells were positive for NAPlr staining and plasmin activity. Treatment of the infection by antibiotics and drainage did not improve the AKI, but steroid administration improved that. NAPlr evaluation is a helpful tool for identifying causes of AIN during infection.

Infection-Related Glomerulonephritis in Children and Adults

Infection-related glomerulonephritis is an immunologically mediated glomerular injury after an infection. Glomerulonephritis may occur with the infection or after a variable latent period. Poststreptococcal glomerulonephritis (PSGN) is the prototype of infection-related glomerulonephritis. The streptococcal antigens, nephritis-associated plasmin-like receptor and streptococcal exotoxin B, have emerged as major players in the pathogenesis of PSGN. Although PSGN is the most common infection-related glomerulonephritis in children, in adults, glomerulonephritis is secondary to bacteria such as staphylococci, viruses such as hepatitis C, and human immunodeficiency virus, and, rarely, parasitic infections. Supportive therapy is the mainstay of treatment in most infection-related glomerulonephritis. Treatment of the underlying infection with specific antibiotics and antiviral medications is indicated in some infections. Parasitic infections, although rare, may be associated with significant morbidity. Poststreptococcal glomerulonephritis is a self-limiting condition with a good prognosis. However, bacterial, viral, and parasitic infections may be associated with significant morbidity and long-term consequences. Epidemiologic studies are required to assess the global burden of infection-related glomerulonephritis. A better understanding of the pathogenesis of infection-related glomerulonephritis may unravel more treatment options and preventive strategies.

Infection-Related Cryoglobulinemic Glomerulonephritis with Serum Anti-Factor B Antibodies Identified and Staining for NAPlr/Plasmin Activity Due to Infective Endocarditis

In this rare case of infection-related cryoglobulinemic glomerulonephritis with infective endocarditis, a 78-year-old male presented with an acute onset of fever and rapidly progressive glomerulonephritis. His blood culture results were positive for Cutibacterium modestum, and transesophageal echocardiography showed vegetation. He was diagnosed with endocarditis. His serum immunoglobulin M, IgM-cryoglobulin, and proteinase-3-anti-neutrophil cytoplasmic antibody levels were elevated, and his serum complement 3 (C3) and C4 levels were decreased. Renal biopsy results showed endocapillary proliferation, mesangial cell proliferation, and no necrotizing lesions on light microscopy, with strong positive staining for IgM, C3, and C1q in the capillary wall. Electron microscopy showed deposits in the mesangial area in the form of fibrous structures without any humps. Histological examination confirmed a diagnosis of cryoglobulinemic glomerulonephritis. Further examination showed the presence of serum anti-factor B antibodies and positive staining for nephritis-associated plasmin receptor and plasmin activity in the glomeruli, suggesting infective endocarditis-induced cryoglobulinemic glomerulonephritis.

Clinico-Pathogenic Similarities and Differences between Infection-Related Glomerulonephritis and C3 Glomerulopathy

Recently, the comprehensive concept of "infection-related glomerulonephritis (IRGN)" has replaced that of postinfectious glomerulonephritis (PIGN) because of the diverse infection patterns, epidemiology, clinical features, and pathogenesis. In addition to evidence of infection, hypocomplementemia particularly depresses serum complement 3 (C3), with endocapillary proliferative and exudative GN developing into membranoproliferative glomerulonephritis (MPGN); also, C3-dominant or co-dominant glomerular immunofluorescence staining is central for diagnosing IRGN. Moreover, nephritis-associated plasmin receptor (NAPlr), originally isolated from the cytoplasmic fraction of group A Streptococci, is vital as an essential inducer of C3-dominant glomerular injury and is a key diagnostic biomarker for IRGN. Meanwhile, "C3 glomerulopathy (C3G)", also showing a histological pattern of MPGN due to acquired or genetic dysregulation of the complement alternative pathway (AP), mimics C3-dominant IRGN. Initially, C3G was characterized by intensive "isolated C3" deposition on glomeruli. However, updated definitions allow for glomerular deposition of other complement factors or immunoglobulins if C3 positivity is dominant and at least two orders of magnitude greater than any other immunoreactant, which makes it challenging to quickly distinguish pathomorphological findings between IRGN and C3G. As for NAPlr, it was demonstrated to induce complement AP activation directly in vitro, and it aggravates glomerular injury in the development of IRGN. A recent report identified anti-factor B autoantibodies as a contributing factor for complement AP activation in pediatric patients with PIGN. Moreover, C3G with glomerular NAPlr deposition without evidence of infection was reported. Taken together, the clinico-pathogenic features of IRGN overlap considerably with those of C3G. In this review, similarities and differences between the two diseases are highlighted.

Epidemiology and Clinical Characteristics of Henoch-Schönlein Purpura Associated with Streptococcal Infection in 217 Children in Hubei Province, China

Objectives The objectives of present study were to analyze the association of the streptococcal infection with childhood Henoch-Schönlein purpura (HSP) in China. Methods: We performed a case-control study over a period of five years to evaluate the epidemiology and clinical characteristics of group A β-hemolytic streptococcal (GABHS) triggered HSP. Results: 1. The frequency of GABHS-triggered HSP was 15.1%, while that of GABHS infection developing HSP in children was 4.7%. 2.The epidemiological characteristics of HSP with streptococcal infection were similar to those of HSP alone. 3. The GABHS-triggered HSP cases had a significantly higher frequency of renal involvement than the noninfectious group. 4. IgA and IgG were significantly increased in the streptococcal infection group than in the noninfectious group, while the levels of C3 and C4 decreased significantly. Conclusions: GABHS infection is the most frequent agent in HSP children, and may aggravate the immune dysfunction and prolong the course of HSP.

Anti-neutrophil Cytoplasmic Antibody-associated Vasculitis Superimposed on Post-streptococcal Acute Glomerulonephritis

A 44-year-old woman was admitted due to gross hematuria and progressive renal dysfunction. Poststreptococcal acute glomerulonephritis (PSAGN) was suspected due to her elevated anti-streptolysin O and anti-streptokinase titers and hypocomplementemia. A renal biopsy showed crescent formation and endocapillary hypercellularity with neutrophil infiltrate. An immunofluorescence analysis showed granular immunoglobulin G and C3 deposition, suggesting immune-complex-type glomerulonephritis. However, myeloperoxidase anti-neutrophil cytoplasmic antibody (ANCA) was positive, and peritubular capillaritis was observed. Furthermore, citrullinated histone H3-positive neutrophils were detected as markers for neutrophil extracellular trap formation. Therefore, she was diagnosed with ANCA-associated vasculitis superimposed on PSAGN that was the main contributor to her progressive renal injury.

Nephritis-Associated Plasmin Receptor (NAPlr): An Essential Inducer of C3-Dominant Glomerular Injury and a Potential Key Diagnostic Biomarker of Infection-Related Glomerulonephritis (IRGN)

Nephritis-associated plasmin receptor (NAPlr) was originally isolated from the cytoplasmic fraction of group A Streptococci, and was found to be the same molecule as streptococcal glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and plasmin receptor (Plr) on the basis of nucleotide and amino acid sequence homology. Its main functions include GAPDH activity, plasmin-binding capacity, and direct activation of the complement alternative pathway (A-P). Plasmin trapped by deposited NAPlr triggers the degradation of extracellular matrix proteins, such as glomerular basement membranes and mesangial matrix, and the accumulation of macrophages and neutrophils, leading to the induction of plasmin-related endocapillary glomerular inflammation. Deposited NAPlr at glomerular endocapillary site directly activates the complement A-P, and the endocapillary release of complement-related anaphylatoxins, C3a and C5a, amplify the in situ endocapillary glomerular inflammation. Subsequently, circulating and in situ-formed immune complexes participate in the glomerular injury resulting in NAPlr-mediated glomerulonephritis. The disease framework of infection-related glomerulonephritis (IRGN) has been further expanded. GAPDH of various bacteria other than Streptococci have been found to react with anti-NAPlr antibodies and to possess plasmin-binding activities, allowing glomerular NAPlr and plasmin activity to be utilized as key biomarkers of IRGN.

Acute Post-Streptococcal Glomerulonephritis In Children: A Comprehensive Review

BACKGROUND

Acute post-streptococcal glomerulonephritis (APSGN) is an immune-complex (ICs) mediated glomerular disease triggered by group A β-hemolytic streptococcus (GAS) or Streptococcus pyogenes infections. APSGN represents a major cause of acquired kidney injury in children.

METHODS

This non-systematic review summarizes recent evidence on APSGN. We discuss the epidemiology, pathogenesis, clinical and laboratory findings, histopathology, treatment and prognosis of the disease.

RESULTS

The median APSGN incidence in children in developing countries is estimated at 24.3/100,000 per year, compared with 6.2/100,000 per year in developed countries. Nephritis-associated plasmin receptor, identified as glyceraldehyde-3-phosphate dehydrogenase, and the cationic cysteine proteinase streptococcal pyrogenic exotoxin B are thought to be two leading streptococcal antigens involved in the pathogenesis of APSGN, which activate the complement system, mainly via the alternative but also the lectin pathway. This process is critical for the generation of inflammation by the ICs deposited in the glomerulus. The classic phenotype is an acute diffuse proliferative glomerulonephritis leading to features of the nephritic syndrome including hematuria, oliguria, hypertension and edema. The histopathology shows that the glomeruli are diffused affected, mostly presenting enlarged glomerular tuffs due to hypercellularity. Proliferative endothelial and mesangial cells and inflammation are also observed. APSGN frequently has spontaneous recovery. There is no specific therapy, but its morbidity and mortality are drastically reduced by the prevention and/or treatment of complications.

CONCLUSION

Despite recent advances, the pathogenesis of APSGN is not fully understood. There is no specific treatment for APSGN. The prognosis is generally good. However some cases may evolve to chronic kidney disease.

A case of pathologically confirmed streptococcal infection-related IgA vasculitis with associated glomerulonephritis and leukocytoclastic cutaneous vasculitis

We report the case of an 80 year-old woman who developed bilateral lower extremity purpura and renal impairment with proteinuria a few days after a transient fever (day 0). High levels of both anti-streptolysin-O antibody (ASO) and anti-streptokinase antibody (ASK), as well as low levels of coagulation factor XIII in serum were noted. Skin biopsy was performed and showed a leukocytoclastic vasculitis with deposition of IgA and C3 in the cutaneous small vessels, indicating IgA vasculitis in the skin. After initiation of oral prednisolone, the skin lesions showed significant improvement. However, renal function and proteinuria gradually worsened from day 12. Kidney biopsy was performed on day 29, which demonstrated a necrotizing and crescentic glomerulonephritis with mesangial deposition of IgA and C3. In addition, the deposition of galactose-deficient IgA1 (Gd-IgA1) was positive on glomeruli and cutaneous small vessels, indicating that the purpura and glomerulonephritis both shared the same Gd-IgA1-related pathogenesis. In addition, the association between the acute streptococcal infection and the IgA vasculitis was confirmed by the deposition of nephritis-associated plasmin receptor (NAPlr) in glomeruli. The patient was treated with steroid pulse and intravenous cyclophosphamide, in addition to the oral prednisolone treatment. Renal function and proteinuria gradually improved, but did not completely recover, as is typically seen with courses of IgA vasculitis in the elderly. In this case, the streptococcal infectionrelated IgA vasculitis was confirmed pathologically by the deposition of both NAPlr and Gd-IgA1 in glomeruli, as well as Gd-IgA1 in the cutaneous small vessels.

Use of Immunosuppressive Therapy in the Treatment of IgA-dominant Infection-related Glomerulonephritis

A 51-year-old Japanese man who experienced colon cancer recurrence following primary and metastatic lesion resection was hospitalized due to facial cellulitis with febrile neutropenia and purpura on his lower extremities after chemotherapy. It was complicated by rapidly progressive glomerulonephritis. He was diagnosed with immunoglobulin A (IgA)-dominant endocapillary proliferative glomerulonephritis based on kidney histology. His glomeruli were positive for the nephritis-associated plasmin receptor, plasmin activity and galactose-deficient IgA1 (Gd-IgA1). A skin biopsy immunofluorescence study revealed IgA deposition within perivascular regions but no Gd-IgA1 deposition. The final diagnosis was IgA-dominant infection-related glomerulonephritis (IRGN). The patient's renal function returned to normal after receiving immunosuppressive therapy that consisted of a glucocorticoid and a cyclophosphamide. Immunosuppressive therapy should be considered in cases of IRGN if the patient's infection is completely under control.

Infections, Reactions of Natural Killer T Cells and Natural Killer Cells, and Kidney Injury

Natural killer T (NKT) cells and NK cells are representative innate immune cells that perform antitumor and antimicrobial functions. The involvement of these cells in various renal diseases, including acute kidney injury (AKI), has recently become evident. Murine NKT cells are activated and cause AKI in response to various stimuli, such as their specific ligand, cytokines, and bacterial components. Both renal vascular endothelial cell injury (via the perforin-mediated pathway) and tubular epithelial cell injury (via the tumor necrosis factor-alpha/Fas ligand pathway) are independently involved in the pathogenesis of AKI. NK cells complement the functions of NKT cells, thereby contributing to the development of infection-associated AKI. Human CD56⁺ T cells, which are a functional counterpart of murine NKT cells, as well as a subpopulation of CD56⁺ NK cells, strongly damage intrinsic renal cells in vitro upon their activation, possibly through mechanisms similar to those in mice. These cells are also thought to be involved in the acute exacerbation of pre-existing glomerulonephritis triggered by infection in humans, and their roles in sepsis-associated AKI are currently under investigation. In this review, we will provide an overview of the recent advances in the understanding of the association among infections, NKT and NK cells, and kidney injury, which is much more profound than previously considered. The important role of liver macrophages in the activation of NKT cells will also be introduced.

The influences of α-hemolytic Streptococcus on class switching and complement activation of human tonsillar cells in IgA nephropathy

While β-hemolytic streptococcus (β-HS) infections are known to predispose patients to acute poststreptococcal glomerulonephritis, there is evidence that implicates α-hemolytic streptococcus (α-HS) in IgA nephropathy (IgAN). The alternative pathway of the complement system has also been implicated in IgAN. We aimed to explore the association between α-HS and complement activation in human tonsillar mononuclear cells (TMCs) in IgAN. In our study, α-HS induced higher IgA levels than IgG levels, while β-HS increased higher IgG levels than IgA levels with more activation-induced cytidine deaminase, in TMCs in the IgAN group. Aberrant IgA1 O-glycosylation levels were higher in IgAN patients with α-HS. C3 and C3b expression was decreased in IgAN patients, but in chronic tonsillitis control patients, the expression decreased only after stimulation with β-HS. Complement factor B and H (CFH) mRNA increased, but the CFH concentration in culture supernatants decreased with α-HS. The percentage of CD19 + CD35 + cells/complement receptor 1 (CR1) decreased with α-HS more than with β-HS, while CD19 + CD21 + cells/complement receptor 2 (CR2) increased more with β-HS than with α-HS. The component nephritis-associated plasmin receptor (NAPlr) of α-HS was not detected on tonsillar or kidney tissues in IgAN patients and was positive on cultured TMCs and mesangial cells. We concluded that α-HS induced the secretion of aberrantly O-glycosylated IgA while decreasing the levels of the inhibitory factor CFH in culture supernatants and CR1 + B cells. These findings provide testable mechanisms that relate α-HS infection to abnormal mucosal responses involving the alternative complement pathway in IgAN.

Nephritis-associated plasmin receptor (NAPlr)-positive glomerulonephritis in a case of ANCA-negative small vessel vasculitis

A 75-year-old man with fever was diagnosed with alveolar hemorrhage. Antineutrophil cytoplasmic antibodies for myeloperoxidase and proteinase 3 were absent. He received corticosteroid therapy, which immediately improved his symptoms and chest radiological findings. After the discontinuation of corticosteroids, fever and general fatigue relapsed, and renal function deteriorated with hematuria and proteinuria. A nerve conduction study revealed mononeuritis multiplex. Renal biopsy demonstrated focal necrotizing crescentic glomerulonephritis with endocapillary proliferative lesions, immunofluorescence C3 deposits, and electron-microscopic subepithelial hump-like deposits. Nephritis-associated plasmin receptor (NAPlr) and plasmin activity, biomarkers of infection-related glomerulonephritis, were positive in glomeruli. Although pathological findings suggested infection-related glomerulonephritis (IRGN), clinical manifestations, such as alveolar hemorrhage and mononeuritis multiplex, suggested systemic small vessel vasculitis. After corticosteroid therapy, systemic symptoms disappeared, and the gradual amelioration of hematuria and proteinuria was observed. Based on the clinical symptoms for which steroid therapy was effective, the patient was considered to have systemic small vessel vasculitis, the etiology of which may have been associated with infection.

A man with immunoglobulin A nephropathy complicated by infection-related glomerulonephritis with glomerular depositions of nephritis-associated plasmin receptor

A 27-year-old man who developed heavy proteinuria with hematuria and acute kidney injury 2 weeks after a fever was referred to our hospital. Because he had low complements without autoantibodies, we clinically diagnosed him with infection-related glomerulonephritis. The proliferation of mesangial cells and endothelial cells with glomerular deposits of immunoglobulin A and complement 3 was found. Deposition of glomerular nephritis-associated plasmin receptor, a marker of infection-related glomerulonephritis, was also found. In addition, the distribution of nephritis-associated plasmin receptor deposition almost perfectly matched the plasmin activity-positive region. Over 3 months later, his symptoms were resolved, although moderate proteinuria and active urine sediment were persistent. He underwent a second renal biopsy, and the histological findings revealed that he had immunoglobulin A nephropathy. Therefore, we diagnosed him with infection-related glomerulonephritis superimposed on immunoglobulin A nephropathy at the first renal biopsy. The glomerular deposition of nephritis-associated plasmin receptor is a useful marker and may cause worsening urinalysis findings after bacterial infection in cases of chronic glomerulonephritis.

Acute post-streptococcal glomerulonephritis: analysis of the pathogenesis

Increasing evidence supports a central role of the immune system in acute post streptococcal glomerulonephritis (APSGN), but the current view of how streptococcal biology affects immunity, and vice versa, remains to be clarified. Renal glomerular immune complex deposition is critical in the initiation of APSGN; however, mechanisms previous to immune complex formation could modulate the initiation and the progression of the disease. Initial and late renal events involved in the nephritis can also be related to host factors and streptococcal factors. In this review we describe the mechanisms reported for the APSGN pathogenesis, the interactions of streptococcal products with renal cells and leukocytes, the possible effects of different nephritogenic antigens in the renal environment and the possibility that APSGN is not just due to a single streptococcal antigen and its antibody; instead, kidney damage may be the result of different factors acting at the same time related to both streptococcus and host factors. Addressing these points should help us to better understand APSGN physiopathology.

Glomerular Deposition of Nephritis-Associated Plasmin Receptor (NAPlr) and Related Plasmin Activity: Key Diagnostic Biomarkers of Bacterial Infection-related Glomerulonephritis

It is widely known that glomerulonephritis (GN) often develops after the curing of an infection, a typical example of which is GN in children following streptococcal infections (poststreptococcal acute glomerulonephritis; PSAGN). On the other hand, the term “infection-related glomerulonephritis (IRGN)” has recently been proposed, because infections are usually ongoing at the time of GN onset in adult patients, particularly in older patients with comorbidities. However, there has been no specific diagnostic biomarker for IRGN, and diagnosis is based on the collection of several clinical and pathological findings and the exclusion of differential diagnoses. Nephritis-associated plasmin receptor (NAPlr) was originally isolated from the cytoplasmic fraction of group A streptococcus as a candidate nephritogenic protein for PSAGN and was found to be the same molecule as streptococcal glyceraldehyde-3-phosphate dehydrogenase and plasmin receptor. NAPlr deposition and related plasmin activity were observed with a similar distribution pattern in the glomeruli of patients with PSAGN. However, glomerular NAPlr deposition and plasmin activity could be observed not only in patients with PSAGN but also in patients with other glomerular diseases, in whom a preceding streptococcal infection was suggested. Furthermore, such glomerular staining patterns have been demonstrated in patients with IRGN induced by bacteria other than streptococci. This review discusses the recent advances in our understanding of the pathogenesis of bacterial IRGN, which is characterized by NAPlr and plasmin as key biomarkers.

Crescentic poststreptococcal acute glomerulonephritis accompanied by small vessel vasculitis: case report of an elderly male

Background

Poststreptococcal acute glomerulonephritis (PSAGN) in the elderly tends to have a severe clinical course and often presents with crescentic necrotizing glomerulonephritis in the renal biopsy. However, vasculitis lesions are unusual.

Case presentation

We present a 71-year-old man who was admitted to our hospital for a recurrent gout attack with a rapid decline of renal function. Low C3 levels and a high anti-streptolysin O titer were observed, while myeloperoxidase- and proteinase 3- antineutrophil cytoplasmic antibody (ANCA) were negative. In addition to cellular crescent and necrosis lesions, diffuse peritubular capillaritis and venulitis as well as small arteriole vasculitis in the glomerular hilus were also apparent. Although granular C3c deposits in the capillary wall and hump lesions were not found, immunofluorescent staining for nephritis-associated plasmin receptor (NAPlr) and in situ zymography for plasmin activity were both positive. We thus diagnosed PSAGN accompanied by small vessel vasculitis. Steroid therapy gradually improved the patient’s renal function, and hemodialysis was discontinued after 1 month.

Conclusions

In our case, streptococcus infection might have concurrently provoked vasculitis, and NAPlr staining was useful for confirming diagnosis.

A Case of Self-Limiting Crescentic Immunoglobulin A Glomerulonephritis Associated with Sternoclavicular Arthritis

Immunoglobulin (Ig) A glomerulonephritis (GN) is a heterogeneous disease affected by various factors. Genetic and other factors "hit" DNA, causing IgA malformation and ultimately glomerular injury. We describe a rare case of crescentic IgA GN with sternoclavicular (SC) arthritis in a 75-year-old woman. Despite active IgA GN with cellular crescents, the patient achieved remission of IgA GN without glucocorticoid therapy after remission of SC arthritis was achieved. Considering the patient's clinical course, this case suggested a relationship between IgA GN and SC arthritis.

Role of Steroids in Post-streptococcal Glomerulonephritis Without Crescents on Renal Biopsy

Steroid is usually indicated in patients with post-streptococcal glomerulonephritis (PSGN) with more than 30% crescents on renal biopsy. The role of steroids in patients without crescentic glomerulonephritis is not clear. We present a 19-year-old male patient who was diagnosed with PSGN three weeks after a sore throat infection. He developed acute renal and respiratory failure requiring hemodialysis and mechanical ventilation. The renal biopsy confirmed PSGN, but did not show severe histological features such as crescents formation. Due to lack of clinical improvement, trials of pulse dose methylprednisolone were initiated with prompt improvement in renal and respiratory function. Our case suggested the potential role of high dose steroids in select patients of PSGN with progressive renal failure, development of multi-organ system deterioration, and failed conservative management irrespective of histological findings.

Risk factors and short-term prognosis of preoperative renal insufficiency in infective endocarditis

Background

The incidence of postoperative complications and the in-hospital mortality rate of infective endocarditis (IE) complicated with renal insufficiency are relatively high. This study aimed to analyze the clinical features, etiological characteristics, diagnosis and treatment, and prognosis of IE with renal insufficiency and to explore the risk factors for renal damage.

Methods

IE patients undergoing valvular surgery between 2008 and 2017 in two cardiac centers were retrospectively analyzed. They were divided into renal insufficiency (RI) [endogenous creatinine clearance rate (Ccr) <60 mL/min/1.73 m²] and normal renal function (NRF) (Ccr ≥60 mL/min/1.73 m²) groups. The disease conditions at admission, etiology, treatment, and prognosis were compared between the two groups. Multivariate regression analysis was performed for the related factors.

Results

A total of 8,055 cases of valvular surgery was performed during the study period. We analyzed 401 IE patients [average age 43.9±15 years; RI, n=56 (14%); NRF, n=345 (86%)], after the exclusion of 2 patients with primary glomerulonephritis. RI patients showed higher perioperative mortality (14.3% vs. 4.5%, P=0.042) and streptococcal infection (71.4% vs. 43.8%, P=0.001) rates. The RI group was also older and had worse heart function, greater decreases in hemoglobin and platelet levels, a higher rate of prosthetic valve involvement, more cases of postoperative dialysis, and worse prognosis (all P<0.05). Binary logistic multivariate regression analysis showed that the incidence of streptococcal infection [odds ratio (OR) =4.271, 95% confidence interval (CI), 1.846-9.884; P=0.001], age ≥51 years (OR =5.138, 95% CI, 2.258-11.694; P<0.001), and New York Heart Association (NYHA) functional class III-IV (OR =10.768, 95% CI, 2.417-47.972; P=0.002) were independent risk factors for preoperative renal insufficiency.

Conclusions

IE patients with preoperative renal insufficiency had a high mortality rate and poor prognosis, with streptococcal infection predisposing to a higher risk of renal insufficiency. Moreover, older the age and worse heart function in IE resulted in a greater risk for renal insufficiency.

Post-infectious Proliferative Glomerulonephritis with Monoclonal Immunoglobulin G Deposits Associated with Complement Factor H Mutation

A 55-year-old man developed rapidly progressive glomerulonephritis and nephrotic syndrome. A kidney biopsy specimen showed diffuse proliferative and crescentic glomerulonephritis with monoclonal IgG1κ, humps, and nephritis-associated plasmin receptor, indicating infection-associated proliferative glomerulonephritis with monoclonal immunoglobulin G deposits (PGNMID). Despite dialysis-dependent renal failure, symptomatic therapy resulted in spontaneous recovery of the renal function, mimicking post-infectious glomerulonephritis (PIGN). A heterozygous complement factor H mutation was detected by comprehensive genetic testing of alternative pathway regulatory genes, which might lead to persistent infection-triggered alternative pathway activation and account for severe glomerulonephritis. Post-infectious PGNMID and PIGN might share common clinical presentations and pathogenesis related to the complement pathway.

Pathological implications of linear immunoglobulin G staining on the glomerular capillary walls in a case of infection-related glomerulonephritis

We report a 32-year-old man with nephrotic syndrome and preceding symptom of infection. He had renal insufficiency, hypocomplementemia, and elevated titer of anti-streptolysin O. Renal biopsy showed mesangial hypercellularity and focal segmental endocapillary hypercellularity with double contour of the glomerular basement membrane (GBM). Immunofluorescence study showed granular C3 staining on the mesangial areas and glomerular capillary walls (GCWs) and linear immunoglobulin G (IgG) staining on GCWs. Electron microscopy revealed sporadic subepithelial humps, discontinuous small and thin deposits in the endothelial side of the GBM and mesangial deposits. He was diagnosed with infection-related glomerulonephritis (IRGN) with the striking finding of linear IgG staining, which is unusual in IRGN. The patient did not have diabetes mellitus or anti-GBM disease. The patient's serum seemed not to contain IgG, which can bind to GCW. He showed normalization of complement within two months after relief from infection symptoms and a trend toward improvement in proteinuria, hematuria and renal function over 14 months. We discuss the possible mechanisms of linear IgG staining in our case based on clinical and experimental studies on IRGN with cationic bacterial protein as antigen.

Pulmonary Renal Syndrome After Streptococcal Pharyngitis: A Case Report

Pulmonary renal syndrome is a class of small vessel vasculitides that are characterized by the dual presentation of diffuse alveolar hemorrhage (DAH) and glomerulonephritis. Pulmonary renal syndrome has multiple etiologies, but its development has been rarely reported following infection with group A streptococcus. We present the case of a 36-year-old Native American male who was transferred to our facility due to refractory hypoxic respiratory failure. He had been diagnosed with streptococcal pharyngitis 2 weeks prior to admission. Given the presence of hemoptysis, bronchoscopy was performed and was consistent with DAH. Urinalysis demonstrated hematuria and proteinuria, in the setting of elevated creatinine and blood urea nitrogen. Additionally, antistreptolysin O titer was positive. Given the constellation of laboratory findings and history of streptococcal pharyngitis, the patient was diagnosed with PRS secondary to streptococcal infection. High-dose methylprednisolone was initiated with concomitant plasmapheresis. He was extubated successfully after his respiratory status improved and was eventually discharged home after making a full recovery within 2 weeks after admission. This case illustrates the importance of clinically relevant sequelae of streptococcal infection as well as the appropriate treatment of PRS secondary to streptococcal pharyngitis with plasmapheresis and intravenous corticosteroids.

Streptococcal Infection-related Nephritis (SIRN) Manifesting Membranoproliferative Glomerulonephritis Type I

We herein report the case of an 18-year-old boy who developed nephrotic syndrome and hypertension after upper airway inflammation. Post-streptococcal acute glomerulonephritis was diagnosed on the basis of a high antistreptolysin O titer, hypocomplementemia, proteinuria, and microscopic hematuria. A renal biopsy was performed due to persistent proteinuria, and the pathological diagnosis was membranoproliferative glomerulonephritis (MPGN) type I. Glomeruli showed positive staining for nephritis-associated plasmin receptor (NAPlr), a nephritogenic group A streptococcal antigen, and plasmin activity was found in a similar distribution as NAPlr deposition. This rare case of streptococcal infection-related nephritis (SIRN) manifesting MPGN type I supports the histological diversity of SIRN.

Diffuse alveolar hemorrhage in a patient with acute poststreptococcal glomerulonephritis caused by impetigo

We herein report a case of pulmonary renal syndrome with nephritis in a 17-year-old boy with diffuse alveolar hemorrhage (DAH) associated with acute poststreptococcal glomerulonephritis (APSGN). The patient exhibited hemoptysis two weeks after developing impetigo, and DAH was diagnosed on bronchoscopy. Respiratory failure progressed, and high-dose methylprednisolone therapy was administered; the respiratory failure regressed immediately after the onset of therapy. Streptococcus pyogenes was detected in an impetigo culture, and, together with the results of the renal biopsy, a diagnosis of APSGN was made. This case demonstrates the effects of high-dose methylprednisolone therapy in improving respiratory failure.

A case of post-pneumococcal acute glomerulonephritis with glomerular depositions of nephritis-associated plasmin receptor

We report the case of a 12-year-old girl who was referred to our hospital with anuria associated with pneumonia. On admission, the patient's blood test results revealed severe renal failure, hypoproteinemia, and hypocomplementemia. Her urinalysis results revealed hematuria, proteinuria, and a positive titer for Streptococcus pneumoniae. S. pneumoniae was also detected in her sputum and blood cultures. The patient was diagnosed with post-pneumococcal acute glomerulonephritis (AGN) with acute renal failure. A renal biopsy demonstrated the infiltration of neutrophils and mononuclear cells into capillary loops. Immunofluorescence studies showed dominant-positive deposition of C3c along the capillary loops and nephritis-associated plasmin receptor (NAPlr) depositions in the mesangial area and capillary loops. Electron microscopy revealed dense deposits in the glomerular basement membrane without a hump in the subepithelial area. These findings were consistent with endocapillary proliferative glomerulonephritis. AGN associated with pneumococcal infection is very rare. This case suggests that NAPlr is the causative antigen not only of post-streptococcal AGN, but also of post-pneumococcal AGN. To our knowledge, this is the first report that shows a relationship between post-pneumococcal AGN and NAPlr depositions in the glomeruli.

Acute post-streptococcal glomerulonephritis with acute kidney injury in nephrotic syndrome with the glomerular deposition of nephritis-associated plasmin receptor antigen

We herein report the case of a 17-year-old man who developed an increased plasma creatinine level (11.1 mg/dL) and oliguria with massive proteinuria (27.3 g/day) four weeks after an abraded wound to his right knee. The histology of the renal biopsy specimens showed diffuse endocapillary proliferative glomerulonephritis with the deposition of nephritis-associated plasmin receptor in the glomerulus. A case of acute kidney injury due to nephrotic syndrome caused by acute post-streptococcal glomerulonephritis was diagnosed. His renal function and proteinuria were improved with supportive care, including hemodialysis, without the administration of immunosuppressive agents.