BK Virus Nephritis Research Articles

Intracellular trafficking pathway of BK Virus in human renal proximal tubular epithelial cells

Intracellular trafficking of BK Virus (BKV) in human renal proximal tubular epithelial cells (HRPTEC) is critical for BKV nephritis. However, the major trafficking components utilized by BKV remain unknown. Coincubation of HRPTEC with BKV and microtubule disrupting agents prevented BKV infection as detected by immunofluorescence and western blot analysis with antibodies which recognize BKV large T antigen. However, inhibition of a dynein, cellular motor protein, did not interfere with BKV infection in HRPTEC. A colocalization study of BKV with the markers of the endoplasmic reticulum (ER) and the Golgi apparatus (GA), indicated that BKV reached the ER from 6 to 10 h, while bypassing the GA or passing through the GA too transiently to be detected. This study contributes to the understanding of mechanisms of intracellular trafficking used by BKV in the infection of HRPTEC.

Caveolar Endocytosis Is Critical for BK Virus Infection of Human Renal Proximal Tubular Epithelial Cells

In recent years, BK virus (BKV) nephritis after renal transplantation has become a severe problem. The exact mechanisms of BKV cell entry and subsequent intracellular trafficking remain unknown. Since human renal proximal tubular epithelial cells (HRPTEC) represent a main natural target of BKV nephritis, analysis of BKV infection of HRPTEC is necessary to obtain additional insights into BKV biology and to develop novel strategies for the treatment of BKV nephritis. We coincubated HRPTEC with BKV and the cholesterol-depleting agents methyl beta cyclodextrin (MBCD) and nystatin (Nys), drugs inhibiting caveolar endocytosis. The percentage of infected cells (detected by immunofluorescence) and the cellular levels of BKV large T antigen expression (detected by Western blot analysis) were significantly decreased in both MBCD- and Nys-treated HPRTEC compared to the level in HRPTEC incubated with BKV alone. HRPTEC infection by BKV was also tested after small interfering RNA (siRNA)-dependent depletion of either the caveolar structural protein caveolin-1 (Cav-1) or clathrin, the major structural protein of clathrin-coated pits. BKV infection was inhibited in HRPTEC transfected with Cav-1 siRNA but not in HRPTEC transfected with clathrin siRNA. The colocalization of labeled BKV particles with either Cav-1 or clathrin was investigated by using fluorescent microscopy and image cross-correlation spectroscopy. The rate of colocalization of BKV with Cav-1 peaked at 4 h after incubation. Colocalization with clathrin was insignificant at all time points. These results suggest that BKV entered into HRPTEC via caveolae, not clathrin-coated pits, and that BKV is maximally associated with caveolae at 4 h after infection, prior to relocation to a different intracellular compartment.

Prospective Evaluation of BK Virus DNAemia in Renal Transplant Patients and Their Transplant Outcome

Background After renal transplantation, the prevalence of BK virus (BKV) viruria, viremia, and nephritis (BKVAN) has been estimated at 30%, 13%, and 8%, respectively. Patients and Methods The aim of this prospective study was to assess the occurrence of BKV DNAemia during the first year after renal transplantation and to determine the prevalence of BKVAN, in the absence of immunosuppression alteration, following positive BKV DNA. BKV DNAemia was assessed systematically in 104 renal transplant patients on postoperative days 60, 90, 135, 180, 270, and 360. Results Of the 104 patients, 7 (6.7%) presented with at least 1 episode of BKV DNAemia. Those with positive BKV DNAemia had a cumulative steroid dose administered from days 0 to 7 which was higher than those without BKV DNAemia (2.13 ± 0.6 vs 1.6 ± 0.4; P = .024). The first BKV DNAemia occurred at 170 (30–460) days posttransplantation. Of the 7 patients who experienced at least 1 BKV DNAemia, 3 had 1 occurrence, but the other 4 had repeated occurrences. These 4 patients developed overt BKVAN at 1 (2 cases) to 2 weeks (2 cases) after the first occurrence of BKV DNAemia. These 4 patients were withdrawn from mycophenolate mofetil, which was in all cases replaced by leflunomide. With a follow-up ranging from 14 to 24 months after the first episode of BKV DNAemia, patient and graft survivals were both 100%. Current serum creatinine ranges from 97 to 173 μmol/L for those who had only 1 episode of BKV DNAemia, and from 144 to 240 μmol/L for those who had overt BKVAN. Conclusion Although BKV DNAemia is a rare event after renal transplantation, it is often associated with BKVAN, which may be treated successfully by the alleviation of immunosuppression and leflunomide therapies.

Pathogenesis of BK virus infection after renal transplantation

BK virus (BKV) was first detected in a renal transplant recipient in 1971 [1]. Increasing incidence of this infection in renal transplant recipients as BKV nephritis (BKVN) poses a threat to graft ...

BK virus infection after renal transplantation

Purpose of review Increasing prevalence of BK virus nephritis after renal transplantation has prompted review of important publications on this topic. Recent findings Nephritis from the BK virus occurs specifically in renal transplant recipients, but not after other solid organ transplantation. A mouse renal transplant model of polyoma nephritis unveils the role of alloimmune activity in the development of BK virus nephritis. BK virus nephritis occurs approximately 1 year after transplantation, as opposed to acute rejection, which occurs early after transplantation. No identifiable donor, recipient, or transplant variables correlate with this disease. Recipients who receive a kidney from a seropositive kidney donor and the lack of HLA C7 in either donor or recipient may play a role in BK virus infection. Mycophenolate mofetil and tacrolimus combination therapy is associated with a slightly higher chance of infection. Recovery from BK virus nephritis is associated with increase in BK virus-specific humoral and cellular immunity, which suggests that they are relevant factors in the pathogenesis of this disease. Summary Nephritis from BK virus infection occurs through seropositive donors. Lack of HLA C7 in donor and recipient and BK virus-specific humoral and cellular immune deficiencies may precipitate infection.

BK virus nephritis: Risk factors, timing, and outcome in renal transplant recipients

BK virus nephritis (BKVN) has emerged as an important cause of renal transplant failure. Quantified analysis of its timing and clinical course is generally lacking. We have thus quantified the timing, risk factors, evolution of renal function, and transplant graft outcome in renal transplant recipients with BKVN from our center. A total of 41 cases of BKVN were diagnosed in 1001 renal and renal/pancreas transplant recipients. There were 2 groups: group I (N= 16), with diagnosis based on renal biopsy alone from January 1996 to August 2001, and group II (N= 25), with diagnosis based on quantitative blood BKV-PCR and biopsy from September 2001 to December 2003. The demographics, the clinical course, immunosuppressive therapy, renal function, and graft outcome were quantified. Donor, recipient, and transplant risk variables were studied using a univariate analysis. Actuarial graft survival was calculated. An immunosuppressive scale created to evaluate the degree of immunosuppression in these patients and its reduction after the diagnosis of BKVN. The median time from transplant to BKVN diagnosis was 318 days (range 48-1356). The actuarial graft survival in patients with BKVN at 6 months, 1, 3, and 5 years was 97%, 90%, 58%, and 47%. The corresponding values for those without BKVN were 94%, 92%, 83%, and 76%, respectively, P < 0.001. Graft loss occurred in 46% of patients. The rate of decline of renal function in group II (N= 25) patients in the 4 months preceding BKVN was rapid (4.8 mL/min/month) and this declined to 0.7 mL/min/month at 3 months' post-BKVN diagnosis, P= 0.004. In those who recovered, the time to stabilization of renal function was a median of 112 days. The immunosuppressive scale score was 7 units at the time of diagnosis of BKVN and decreased to 3.5 units at 3 months' post-BKVN. Reduction in the dose of calcineurin inhibitors but not the overall reduction in dose of immunosuppression correlated with recovery of renal function in these patients. BKVN is a relatively late complication of renal transplantation. Despite reduction in immunosuppression, graft loss occurred in 46% of patients. There was a steep decline in renal function in months preceding the diagnosis of BKVN, and reduction in calcineurin inhibitor dose, but not overall immunosuppression, correlated with stabilization of renal function.

HLA Mismatching Increases the Risk of BK Virus Nephropathy in Renal Transplant Recipients

BK virus (BKV)nephropathy is a serious complication in kidney transplant recipients that may lead to irreversible graft failure. We have analyzed the degree of donor/recipient HLA compatibility and HLA antigen association in 40 kidney transplant patients with BKV nephropathy in comparison with a control group of 404 unaffected transplant recipients who were on tacrolimus-based immunosuppression with no induction. HLA compatibility was assessed by determining the number of HLA-A, -B, -DR-mismatched antigens. BK virus nephropathy was diagnosed histologically and confirmed by immunochemistry. Univariate and multiple logistic regression statistical analyses have shown a significant association between BKV nephropathy and HLA mismatching. This analysis showed also that BKV nephritis is associated with a greater number of rejection episodes and a higher incidence of steroid-resistant rejection requiring antilymphocyte treatment. There was no association between BKV nephropathy and any specific HLA allele. We propose that HLA mismatching promotes the development of BKV nephropathy through rejection-related inflammatory processes and heavy immunosuppression which cause virus reactivation and injury of the tubular epithelium.

Elevation of CXCR3-Binding Chemokines in Urine Indicates Acute Renal-Allograft Dysfunction

A noninvasive urinary test that diagnoses acute renal allograft dysfunction would benefit renal transplant patients. We aimed to develop a rapid urinary diagnostic test by detecting chemokines. Seventy-three patients with renal allograft dysfunction prompting biopsy and 26 patients with stable graft function were recruited. Urinary levels of CXCR3-binding chemokines, monokine induced by IFN-γ (Mig/CXCL9), IFN-γ-induced protein of 10 kDa (IP-10/CXCL10), and IFN-inducible T-cell chemoattractant (I-TAC/CXCL11), were determined by a particle-based triplex assay. IP-10, Mig and I-TAC were significantly elevated in renal graft recipients with acute rejection, acute tubular injury and BK virus nephritis. Using 100 pg/mL as the threshold level, both IP-10 and Mig had diagnostic value (sensitivity 86.4%; specificity 91.3%) in differentiating acute graft dysfunction from other clinical conditions. In terms of monitoring the response to antirejection therapy, this urinary test is more sensitive and predictive than serum creatinine. These results indicate that this rapid test is clinically useful.

Noninvasive diagnosis of BK virus nephritis by measurement of messenger RNA for BK virus VP1 in urine.

Polyoma virus type BK (BKV) nephritis has emerged as an important cause of renal allograft dysfunction and graft failure. Its diagnosis is contingent on the invasive procedure of allograft biopsy. A noninvasive diagnostic test for BKV nephritis could improve clinical outcome. We obtained 25 urine specimens from 8 renal allograft recipients with biopsy-confirmed BKV nephritis, 31 samples from 28 recipients in whom BKV nephritis was excluded by allograft biopsy, and 74 specimens from 34 patients with stable allograft function. RNA was isolated from the urinary cells and reverse transcribed to complementary DNA. We designed gene-specific oligonucleotide primers and probes for the measurement of messenger RNA (mRNA) encoding BKV VP1 protein and a constitutively expressed 18S ribosomal RNA (rRNA) by real-time quantitative polymerase chain reaction. We explored the hypothesis that BKV VP1 mRNA levels predict BKV nephritis. The levels of BKV VP1 mRNA but not the levels of 18S rRNA predicted BKV nephritis. Analysis involving the receiver operating characteristic curve demonstrated that BKV nephritis can be predicted with a sensitivity of 93.8% and a specificity of 93.9% with the use of a cutoff value of 6.5 x 10 BKV VP1 mRNA copy number per nanogram of total RNA ( <0.00001). In the receiver operating characteristic curve analysis, the calculated area under the curve was 0.949 (95% confidence interval, 0.912 to 0.987, <0.00001) for BKV VP1 mRNA levels and 0.562 (95% confidence interval, 0.417 to 0.708, >0.2) for 18S rRNA. Measurement of BKV VP1 mRNA in urinary cells offers a noninvasive and accurate means of diagnosing BKV nephritis.

BK virus regulatory region rearrangements in brain and cerebrospinal fluid from a leukemia patient with tubulointerstitial nephritis and meningoencephalitis

BK virus (BKV) was recovered by polymerase chain reaction (PCR) from brain, kidney, lung, urine, and cerebrospinal fluid (CSF) of a fatal case of BKV tubulointerstitial nephritis with dissemination to lung and brain. Viral regulatory regions in PCR-amplified urine and the lung samples were identical to the archetypal structure, WWT. In the brain and CSF, a rearranged sequence predominated, however. A 94-bp deletion preceded a 71-bp tandem duplication because the same 94-bp segment was deleted from both copies. PCR-amplified regulatory region products were cloned and sequenced to define further the extent of the rearranged structures. Two kidney clones were archetypal, whereas two others were rearranged differently from the brain and from each other. In contrast to the brain clones, the kidney rearrangements seemed to involve deletion after duplication. Three of four brain clones sequenced were identical to the rearrangement found to dominate in the PCR product. A fourth clone showed two short deletions without any duplication. The four CSF clones all showed rearrangements identical to that which was amplified by PCR from CSF and brain. This represents the first molecular analysis of a BKV strain obtained from a central nervous system infection, and it reveals regulatory region rearrangements reminiscent of those described in JC virus from brains with progressive multifocal leukoencephalopathy. We suggest that the presence in the CSF of BKV with a dominant rearranged regulatory region may be useful in the diagnosis of BKV meningoencephalitis secondary to BKV nephritis. © 2002 by the National Kidney Foundation, Inc.