[Kidney damage in COVID-19]. / Les atteintes rénales de la COVID-19.

COVID-19 is a disease caused by the RNA virus SARS-CoV-2. It is characterised by an attack mainly affecting the respiratory system. There is renal involvement which is characterised by three main types of damage, acute tubular necrosis occurring in the most severe cases, proximal tubulopathy which is a prognostic marker of the disease and segmental and focal hyalinosis occurring in a genetically predisposed terrain. The pathophysiology of SARS-CoV-2 renal involvement is not yet defined. The direct role of the virus is debated, whereas the cytokine storm and the hypoxic and thrombotic complications seem more important. The long-term outcome of the renal damage appears to be quite good. Long-term follow-up will allow us to say whether the renal damage is part of the long COVID.

COVID-19 Recovery Without B Cells or Antibodies in Patients Receiving Rituximab for Autoimmune Disease.

No Abstract.

APOL1 risk variants and the development of HIV-associated nephropathy.

HIV-associated nephropathy (HIVAN) remains a concern among untreated HIV patients, notably of African descent, as patients can reach end-stage renal disease within 3 years. Two variants (G1 and G2) of the APOL1 gene, common in African populations to protect against African sleeping sickness, have been associated with an increased risk of several glomerular disorders including HIVAN, hypertension-attributed chronic kidney disease, and idiopathic focal segmental glomerulosclerosis and are accordingly named renal risk variants (RRVs). This review examines the mechanisms by which APOL1 RRVs drive glomerular injury in the setting of HIV infection and their potential application to patient management. Innate antiviral mechanisms activated by chronic HIV infection, especially those involving type 1 interferons, are of particular interest as they have been shown to upregulate APOL1 expression. Additionally, the downregulation of miRNA 193a (a repressor of APOL1) is also associated with the upregulation of APOL1. Interestingly, glomerular damage affected by APOL1 RRVs is caused by both loss- and gain-of-function changes in the protein, explicitly characterizing these effects. Their intracellular localization offers a further understanding of the nuances of APOL1 variant effects in promoting renal disease. Finally, although APOL1 variants have been recognized as a critical genetic player in mediating kidney disease, there are significant gaps in their application to patient management for screening, diagnosis, and treatment.

Collapsing Focal Segmental Glomerulosclerosis in Viral Infections.

Collapsing glomerulopathy represents a special variant of the proteinuric kidney disease focal segmental glomerulosclerosis (FSGS). Histologically, the collapsing form of FSGS (cFSGS) is characterized by segmental or global condensation and obliteration of glomerular capillaries, the appearance of hyperplastic and hypertrophic podocytes and severe tubulointerstitial damage. Clinically, cFSGS patients present with acute kidney injury, nephrotic-range proteinuria and are at a high risk of rapid progression to irreversible kidney failure. cFSGS can be attributed to numerous etiologies, namely, viral infections like HIV, cytomegalovirus, Epstein-Barr-Virus, and parvovirus B19 and also drugs and severe ischemia. Risk variants of the APOL1 gene, predominantly found in people of African descent, increase the risk of developing cFSGS. Patients infected with the new Corona-Virus SARS-CoV-2 display an increased rate of acute kidney injury (AKI) in severe cases of COVID-19. Besides hemodynamic instability, cytokine mediated injury and direct viral entry and infection of renal epithelial cells contributing to AKI, there are emerging reports of cFSGS associated with SARS-CoV-2 infection in patients of mainly African ethnicity. The pathogenesis of cFSGS is proposed to be linked with direct viral infection of podocytes, as described for HIV-associated glomerulopathy. Nevertheless, there is growing evidence that the systemic inflammatory cascade, activated in acute viral infections like COVID-19, is a major contributor to the impairment of basic cellular functions in podocytes. This mini review will summarize the current knowledge on cFSGS associated with viral infections with a special focus on the influence of systemic immune responses and potential mechanisms propagating the development of cFSGS.

De novo CMV-associated collapsing focal segmental glomerulosclerosis in a kidney transplant recipient.

Collapsing focal segmental glomerulosclerosis (FSGS) is a variant of FSGS and is associated with severe nephrotic syndrome and acute kidney injury and can occur after kidney transplantation. The exact mechanism of collapsing FSGS after kidney transplantation is unknown, but potential causes include autoimmune diseases, certain malignancies, bisphosphonates, m-TOR inhibitors, interferon-alpha, HIV infection, and other viruses. We describe a case of de novo Cytomegalovirus (CMV)-associated collapsing FSGS in a kidney transplant recipient with a UL97 phosphotransferase mutation that was successfully treated with intravenous ganciclovir, intravenous immunoglobulin, and steroids.

[Collapsing focal segmental glomerulosclerosis induced by cytomegalovirus: A case report]. / Hyalinose segmentaire et focale collapsante secondaire au cytomégalovirus : à propos d'un cas.

Focal segmental glomerulosclerosis (FSGS) is a common cause of nephrotic syndrome in child and adult. The collapsing forms are of poor renal prognosis and are usually secondary to viral infections with, first and foremost, the human immunodeficiency virus. Among other viral etiologies, cytomegalovirus (CMV) is an uncommon cause. We report a case of a 32years-old patient with collapsing focal segmental glomerulosclerosis induced by cytomegalovirus with initial acute renal failure and proteinuria at 12.4g/24h. The treatment associated ganciclovir during 7days followed by valganciclovir during 14days and steroids at 1mg/kg/day. Renal function improved and proteinuria decreased with this treatment. Proteinuria increase again 3weeks after valganciclovir discontinuation while CMV Polymerase chain reaction (PCR) was positive. Therefore, valganciclovir has been resumed allowing renal function normalization and decrease in proteinuria to 4g/24h after negative CMVPCR assay after 15weeks. Anti-CMV therapy combined with steroids seems to provide a renal response in case of FSGS induced by CMV even if long-term prognosis stays uncertain.

Infection-Related Focal Segmental Glomerulosclerosis in Children.

Focal segmental glomerulosclerosis (FSGS) is the most common cause of steroid resistant nephrotic syndrome in children. It describes a unique histological picture of glomerular damage resulting from several causes. In the majority of patients the causing agent is still unknown, but in some cases viral association is evident. In adults, the most established FSGS causing virus is the human immune-deficiency virus, which is related to a collapsing variant of FSGS. Nevertheless, other viruses are also suspected for causing a collapsing or noncollapsing variant, for example, hepatitis B virus, parvovirus B19, and Cytomegalovirus. Although the systemic infection mechanism is different for these viruses, there are similarities in the pathomechanism for the induction of FSGS. As the podocyte is the key structure in the pathogenesis of FSGS, a direct infection of these cells or immediate damage through the virus or viral components has to be considered. Although viral infections are a very rare cause for FSGS in children, the treating pediatric nephrologist has to be aware of a possible underlying infection, as this has a relevant impact on therapy and prognosis.

[Collapsing variant of focal segmental glomerulosclerosis by parvovirus B19: case report]. / Glomeruloesclerose segmentar e focal (GESF) colapsante associada ao parvovírus B19: relato de caso.

OBJECTIVE: To describe the clinical and laboratory profile of focal segmental glomerulosclerosis (FSGS) of the collapsing subtype in association with infection by parvovirus B19 (PVB19). CASE REPORT: Female patient, 37 years old, mulatto, developed pharyngalgia and fever with partial improvement after penicillin. After one week we observed reduced urinary output and lower limb edema. Smoker, family and personal history negative for hypertension, diabetes or kidney disease. Patient presented with olyguria, hypertension and edema, also hypochromic microcytic hypoproliferative anemia, nephritic range proteinuria, microscopic hematuria and renal dysfunction. All rheumatologic investigation, HIV and hepatitis serology were negative. Unremarkable renal ultrasound. PCR positive for PVB19 in bone marrow aspirate and blood and renal biopsy conclusive of collapsing FSGS subtype. Spontaneous remission occurred within two weeks of the profile. The blood PVB19 PCR was repeated within a month and resulted negative. This finding demonstrated PVB19 acute infection or viral reactivation in association with collapsing FSGS. CONCLUSION: There is demonstrated the temporal association of PVB19 viremia and collapsing FSGS, due primary infection or viral reactivation. The association of collapsing FSGS and PVB19 is described in the literature, demonstrating virus presence in kidney tissue, but the real relationship of virus in the pathogenesis of this glomerulopathy remains unclear.

Glomeruloesclerose segmentar e focal (GESF) colapsante associada ao parvovírus B19: relato de caso / Collapsing variant of focal segmental glomerulosclerosis by parvovirus B19: case report

Objetivo: Descrever quadro clínico-laboratorial de glomeruloesclerose segmentar e focal (GESF) subtipo colapsante em associação com infecção por parvovírus B19 (PVB19). Relato do caso: Paciente feminino, 37 anos, parda, iniciou quadro de faringoalgia e febre aferida com melhora parcial após penicilina. Com uma semana, observou redução de débito urinário e edema de membros inferiores. Tabagista, com histórico familiar e pessoal negativos para hipertensão, diabetes ou nefropatias. À admissão, apresentava-se com oliguria, hipertensão e edema, associados à anemia microcítica e hipocrômica hipoproliferativa, proteinúria nefrótica, hematúria microscópica e alteração da função renal. A investigação reumatológica e sorologias para hepatites e HIV foram negativas. Ultrassonografia de rins e vias urinárias sem alterações. PCR foi positivo para PVB19 em aspirado de medula óssea e sangue. A biópsia renal conclusiva de GESF subtipo colapsante. Ocorreu remissão espontânea com duas semanas do quadro. Em retorno ambulatorial, o PCR em sangue periférico foi negativo para PVB19, sugerindo associação de GESF colapsante a fase aguda ou reativação da infecção viral. Conclusão : Este relato registra a associação temporal entre GESF colapsante e viremia pelo PVB19, seja por infecção aguda ou reativação de infecção latente. A associação GESF colapsante e PVB19 é descrita na literatura, com demonstração da presença do vírus em tecido renal, porém, a real relação do vírus na patogênese dessa glomerulopatia permanece indefinida. .

Objective: To describe the clinical and laboratory profile of focal segmental glomerulosclerosis (FSGS) of the collapsing subtype in association with infection by parvovirus B19 (PVB19). Case report: Female patient, 37 years old, mulatto, developed pharyngalgia and fever with partial improvement after penicillin. After one week we observed reduced urinary output and lower limb edema. Smoker, family and personal history negative for hypertension, diabetes or kidney disease. Patient presented with olyguria, hypertension and edema, also hypochromic microcytic hypoproliferative anemia, nephritic range proteinuria, microscopic hematuria and renal dysfunction. All rheumatologic investigation, HIV and hepatitis serology were negative. Unremarkable renal ultrasound. PCR positive for PVB19 in bone marrow aspirate and blood and renal biopsy conclusive of collapsing FSGS subtype. Spontaneous remission occurred within two weeks of the profile. The blood PVB19 PCR was repeated within a month and resulted negative. This finding demonstrated PVB19 acute infection or viral reactivation in association with collapsing FSGS. Conclusion: There is demonstrated the temporal association of PVB19 viremia and collapsing FSGS, due primary infection or viral reactivation. The association of collapsing FSGS and PVB19 is described in the literature, demonstrating virus presence in kidney tissue, but the real relationship of virus in the pathogenesis of this glomerulopathy remains unclear. .

Krüppel-like factor 6 regulates mitochondrial function in the kidney.

Maintenance of mitochondrial structure and function is critical for preventing podocyte apoptosis and eventual glomerulosclerosis in the kidney; however, the transcription factors that regulate mitochondrial function in podocyte injury remain to be identified. Here, we identified Krüppel-like factor 6 (KLF6), a zinc finger domain transcription factor, as an essential regulator of mitochondrial function in podocyte apoptosis. We observed that podocyte-specific deletion of Klf6 increased the susceptibility of a resistant mouse strain to adriamycin-induced (ADR-induced) focal segmental glomerulosclerosis (FSGS). KLF6 expression was induced early in response to ADR in mice and cultured human podocytes, and prevented mitochondrial dysfunction and activation of intrinsic apoptotic pathways in these podocytes. Promoter analysis and chromatin immunoprecipitation studies revealed that putative KLF6 transcriptional binding sites are present in the promoter of the mitochondrial cytochrome c oxidase assembly gene (SCO2), which is critical for preventing cytochrome c release and activation of the intrinsic apoptotic pathway. Additionally, KLF6 expression was reduced in podocytes from HIV-1 transgenic mice as well as in renal biopsies from patients with HIV-associated nephropathy (HIVAN) and FSGS. Together, these findings indicate that KLF6-dependent regulation of the cytochrome c oxidase assembly gene is critical for maintaining mitochondrial function and preventing podocyte apoptosis.

Hepatitis C virus associated glomerulopathies.

Hepatitis C virus (HCV) infection is a systemic disorder which is often associated with a number of extrahepatic manifestations including glomerulopathies. Patients with HCV infection were found to have a higher risk of end-stage renal disease. HCV positivity has also been linked to lower graft and patient survivals after kidney transplantation. Various histological types of renal diseases are reported in association with HCV infection including membranoproliferative glomerulonephritis (MPGN), membranous nephropathy, focal segmental glomerulosclerosis, fibrillary glomerulonephritis, immunotactoid glomerulopathy, IgA nephropathy, renal thrombotic microangiopathy, vasculitic renal involvement and interstitial nephritis. The most common type of HCV associated glomerulopathy is type I MPGN associated with type II mixed cryoglobulinemia. Clinically, typical renal manifestations in HCV-infected patients include proteinuria, microscopic hematuria, hypertension, acute nephritis and nephrotic syndrome. Three approaches may be suggested for the treatment of HCV-associated glomerulopathies and cryoglobulinemic renal disease: (1) antiviral therapy to prevent the further direct damage of HCV on kidneys and synthesis of immune-complexes; (2) B-cell depletion therapy to prevent formation of immune-complexes and cryoglobulins; and (3) nonspecific immunosuppressive therapy targeting inflammatory cells to prevent the synthesis of immune-complexes and to treat cryoglobulin associated vasculitis. In patients with moderate proteinuria and stable renal functions, anti-HCV therapy is advised to be started as pegylated interferon-α plus ribavirin. However in patients with nephrotic-range proteinuria and/or progressive kidney injury and other serious extra-renal manifestations, immunosuppressive therapy with cyclophosphamide, rituximab, steroid pulses and plasmapheresis should be administrated.

Modulation of renin angiotensin system predominantly alters sclerotic phenotype of glomeruli in HIVAN.

HIV-associated nephropathy (HIVAN) is a common complication of HIV-1 infection in patients with African ancestry in general and with APOL1 gene risk variants in particular. Although collapsing glomerulopathy is considered a hallmark of HIVAN, significant numbers of glomeruli in patients with HIVAN also display other variants of focal segmental glomerulosclerosis (FSGS). We propose that collapsed glomeruli as well as glomeruli with other variants of FSGS are manifestations of HIVAN and their prevalence depends on associated host factors. We explored the role of the renin-angiotensin system (RAS) in the manifestation of any specific glomerular phenotype in HIVAN. To evaluate the role of the RAS we have used a genetically engineered mouse model of HIVAN (Tg26) with two and four copies of angiotensinogen (Agt) gene (Tg26/Agt2 and Tg26/Agt4). In Tg26/Agt2, 1 out of 6 glomeruli exhibited sclerosed phenotype, whereas 1 out of 25 glomeruli displayed collapsed phenotype; on the other hand, in Tg26/Agt4, 1 out of 3 glomeruli exhibited sclerotic phenotype and only 1 out of 7 glomeruli showed collapsed phenotype. To inhibit the effect of RAS, Tg26/Agt2 were administered captopril, aliskiren, aliskiren plus captopril or aliskiren plus telmisartan by miniosmotic pumps for 4 weeks. In all experimental groups there was a significant reduction in percentage of sclerosed glomeruli and only minimal reduction in collapsed glomeruli compared to normal saline receiving Tg26/Agt2. These findings suggest that the manifestation of the sclerosed phenotype in HIVAN is predominantly dependent on activation of the RAS.

Long-term response to peginterferon in hepatitis C virus-associated nephrotic syndrome from focal segmental glomerulosclerosis.

Hepatitis C virus (HCV) infection is a global public health problem. Chronic HCV infection is an important cause of chronic liver disease. Since the first reported association between HCV and membranoproliferative glomerulonephritis (MPGN) in 1993, HCV has been described with other types of glomerular diseases, although less frequently. Focal segmental glomerulosclerosis (FSGS) is one such glomerular disease that has been rarely reported in association with HCV. Antiviral therapy with interferon and ribavirin has been shown to be beneficial in HCV-associated MPGN. The optimal therapy of HCV-associated FSGS is not currently known. To our knowledge, long-term response to pegylated interferon monotherapy in treatment of HCV-associated FSGS has not been reported. We report an adult patient with HCV-associated FSGS who presented with nephrotic syndrome and renal failure. Treatment with pegylated interferon alfa-2a monotherapy resulted in sustained virological response with a clinical remission of nephrotic syndrome and stabilization of renal function. Patient continued to remain in clinical remission of nephrotic syndrome with stable renal function, 5 years after treatment. We also briefly review the literature on HCV-associated glomerular diseases, particularly HCV-associated FSGS.

Stabilization of hepatitis C associated collapsing focal segmental glomerulosclerosis with interferon alpha-2a and ribavirin.

Hepatitis C virus (HCV) infection is associated with a variety of glomerular diseases, most notably cryoglobulin associated membranoproliferative glomerulonephritis Type I. Focal segmental glomerulosclerosis has only rarely been reported in association with HCV. More striking are multiple reports of de novo collapsing focal segmental glomerulosclerosis (cFSGS) developing during administration of interferon for treatment of HCV. Herein is presented a case of HCV associated cFSGS stabilized with combination therapy of interferon α-2a and ribavirin in a patient with advanced kidney disease.

Acute kidney injury in a girl with ulcerative colitis and cytomegalovirus-induced focal segmental glomerular sclerosis.

BACKGROUND: Mesalamine or 5-aminosalicylic acid (5-ASA) has proven efficacy in treating patients with ulcerative colitis (UC). Although mesalamine is considered safe, it has been associated with acute interstitial nephritis and renal failure. METHODS: Herein we present a case of a child with UC who developed acute renal failure on mesalamine therapy. RESULTS: A 15-year-old African-American girl with well-controlled UC presented to the Johns Hopkins Hospital with a four-day history of high fever, malaise, generalized body aches, and productive non-bloody cough. Over the next three days, she developed acute renal failure with fluid retention, and elevated serum creatinine and blood urea nitrogen. A kidney biopsy showed drug induced acute interstitial nephritis and focal segmental glomerulosclerosis with viral inclusion bodies likely secondary to cytomegalovirus. CONCLUSION: When treating UC patients with a history of underlying renal disease, it is advised to carefully monitor renal function while on mesalamine therapy.

[Glomerular diseases in HIV-infected patients: clinical and morphological evaluation].

AIM: To evaluate the clinical and morphological variants of kidney abnormalities in HIV-infected patients. SUBJECTS AND METHODS: Thirty HIV-infected patients (60% men and 40% women) aged 26 to 54 years (mean age 31.6 +/- 4.7 years) who had undergone diagnostic needle renal biopsy were examined. The indication for the biopsy was nephrotic syndrome (NS) (isolated or concurrent acute nephritic syndrome) and/or decreased renal function. The morphological study of biopsy specimens included light microscopy and immunofluorescence assay. RESULTS: In the examined HIV-infected patients, the histological variants of kidney abnormalities presented with immune complex glomerulonephritis (ICGN) in 26 cases and with focal segmental glomerulosclerosis (FSGS) in 4 cases. The clinical manifestations of ICGN were as follows: NS (61.5%), acute nephritic syndrome (in more than one third of the patients) concurrent with hematuria, as well as mainly grades 2-3 arterial hypertension (AH) (12/14) and renal dysfunction. Immune complex glomerulopathies were marked by polymorphism in the renal morphological pattern with fluorescence during immunofluorescence microscopy in most cases of virtually all classes of immunoglobulins (IgA, IgM, IgG) and complement system fragments (C3, C1q). FSGS was clinically characterized by NS concurrent with AH, hematuria. The morphological subtypes of FSGS were exhibited by apical, perihilar, and nonspecific variants in 1, 1, and 2 cases, respectively. By the time the signs of renal dysfunction appeared, the HIV-infected patients with glomerulopathy were found to have a high viral load (HIV RNA >100 000 copies/ml) and low CD4 lymphocyte levels (< or = 200 in 1 microl). CONCLUSION: In our study, the morphological pattern of chronic glomerulonephritis showed a preponderance of immune complex nephropathies with the clinical manifestations of acute nephritic syndrome and/or NS concurrent with hematuria. High viremia and depressed immune system may be risk factors for nephropathy.

HIV-associated nephropathy: experimental models.

Since 1984 reports of renal involvement in AIDS patients have been presented in the literature. Different forms of renal disease were noted in the AIDS population including those related to systemic and local renal infections, tubulointerstitial disease, renal involvement by neoplasm and glomerular disease including collapsing glomerulopathy (CG). HIV-associated nephropathy (HIVAN) has been demonstrated to be more severe in the black population. HIVAN is the most common cause of renal failure in HIV-1-seropositive patients. The term HIVAN is reserved for the typical histopathological form of focal and segmental glomerulosclerosis (FSGS) characterized by the findings of coexistent glomerular and severe tubulointerstitial disease. In both humans and the murine model, glomerular lesions include FSGS, glomerular collapse and podocyte hyperplasia. The tubulointerstitial damage as well as the glomerular collapse can also be seen in non-HIV primary collapsing GN, raising the question of common mechanisms to HIV and other non-identified viral agents related to the development of the disease. Although controversial, increasing evidence supports a direct effect of the virus on renal cells either as a result of exposure to viral proteins or direct renal parenchyma infection. The use of a HIV-1 transgenic mouse model has demonstrated a direct etiologic link between HIV-1 expression in kidney and the development of HIVAN with unique viral-host interactions, which depend at the same time on stimulating features of the virus and the individual nature of the host response. The infection of renal cells by HIV-1 could be detected by reverse transcription-polymerase chain reaction (RT-PCR) of gag RNA at a low level. Some studies using an HIV-1 transgenic mouse model have demonstrated that expression of HIV- 1 in the kidney is required for the development of HIVAN. The final common pathway in the development of HIV-associated nephropathy is likely to involve alterations in the patterns of gene expression of renal parenchyma cells by cytokines and growth factors, leading to interstitial fibrosis and enhanced glomerular matrix synthesis. The nature of the host response to viral infection is critical to the development of nephropathy.HLA-linked responses particular to a subset of blacks may explain some of the epidemiologic features of HIVAN. There may also be biological heterogeneity in the strains of HIV-1 that could account for a particular renotropic strain. HIV strains from different parts of the world may vary by as much as 15% at the level of nucleotide sequence. The infectivity of human immunodeficiency virus (HIV-1) in human glomerular cells has been evaluated by exposing homogeneous cultures of human glomerular capillary endothelial, mesangial and epithelial cells to HIV in vitro. The mechanism of access of HIV into glomerular endothelial and mesangial cells is unknown up to now; HIV is generally infectious for cells expressing the CD4 antigen in their cell membrane. Other modes of HIV entry into cells independent of the CD4 receptor are possible through mechanisms involving Fc-receptors or coinfection with other enveloped viruses such as HTLV-l. Our understanding of the pathogenesis of HIVAN has been aided by the development of a transgenic model. The curious fact that only 3 of 8 founded transgenic lines developed nephropathy emphasizes that the expression of viral gene products per se is not sufficient to produce nephropathy. Human renal epithelium does not express CD4 receptors and in vitro attempts to infect glomerular epithelial cells using laboratory strains of HIV-1 have proven fruitless. The striking morphologic and phenotypic similarities between HIVAN and collapsing idiopathic FSGS raise the question whether the altered podocyte gene expression in collapsing idiopathic FSGS may also be due to a viral infection. This hypothesis is further supported by de novo occurrence of collapsing idiopathic FSGS in immunosuppressed renal transplantation patients and by epidemiologic data. In conclusion, there are likely to be common mechanisms in the pathogenesis for collapsing idiopathic glomerulosclerosis and HIVAN. A primary injury of the podocyte leading to dysregulation of the cellular phenotype appears to mediate the glomerular tuft collapse in both conditions. Primary collapsing glomerulopathy recurs post-transplantation, raising the possibility of circulating factors implicated in the pathogenesis of visceral epithelial cell damage in steroid-resistant minimal change disease or recurrent FSGS. Recurrence of CG can occur hours after transplantation, suggesting that the plasma of CG patients contains one or more factors capable of inducing proteinuria due to the damage of the podocyte that results in the increase in glomerular permeability. In a rat model of CG developed by our group, the injection of serum from CG patients resulted in proteinuria, glomerular tuft retraction and podocyte damage at the ultrastructural level (visceral epithelial cell foot-process effacement). No ultrastructural or light microscopy abnormalities were seen in rats injected with serum from non-collapsing FSGS or healthy subjects. Based on the experience of our group, circulating factors play a dominant role in the pathogenesis of idiopathic CG.