Proteinuria is accompanied by intratubular complement activation and apical membrane deposition of C3dg and C5b-9 in kidney transplant recipients.

Proteinuria predicts accelerated decline in kidney function in kidney transplant recipients (KTRs). We hypothesized that aberrant filtration of complement factors causes intraluminal activation, apical membrane attack on tubular cells, and progressive injury. Biobanked samples from two previous studies in albuminuric KTRs were used. The complement-activation split products C3c, C3dg, and soluble C5b-9-associated C9 neoantigen were analyzed by ELISA in urine and plasma using neoepitope-specific antibodies. Urinary extracellular vesicles (uEVs) were enriched by lectin and immunoaffinity isolation and analyzed by immunoblot analysis. Urine complement excretion increased significantly in KTRs with an albumin-to-creatinine ratio of ≥300 mg/g compared with <30 mg/g. Urine C3dg and C9 neoantigen excretion correlated significantly to changes in albumin excretion from 3 to 12 mo after transplantation. Fractional excretion of C9 neoantigen was significantly higher than for albumin, indicating postfiltration generation. C9 neoantigen was detected in uEVs in six of the nine albuminuric KTRs but was absent in non-albuminuric controls (n = 8). In C9 neoantigen-positive KTRs, lectin affinity enrichment of uEVs from the proximal tubules yielded signal for iC3b, C3dg, C9 neoantigen, and Na+-glucose transporter 2 but only weakly for aquaporin 2. Coisolation of podocyte markers and Tamm-Horsfall protein was minimal. Our findings show that albuminuria is associated with aberrant filtration and intratubular activation of complement with deposition of C3 activation split products and C5b-9-associated C9 neoantigen on uEVs from the proximal tubular apical membrane. Intratubular complement activation may contribute to progressive kidney injury in proteinuric kidney grafts.NEW & NOTEWORTHY The present study proposes a mechanistic coupling between proteinuria and aberrant filtration of complement precursors, intratubular complement activation, and apical membrane attack in kidney transplant recipients. C3dg and C5b-9-associated C9 neoantigen associate with proximal tubular apical membranes as demonstrated in urine extracellular vesicles. The discovery suggests intratubular complement as a mediator between proteinuria and progressive kidney damage. Inhibitors of soluble and/or luminal complement activation with access to the tubular lumen may be beneficial.

Expression of immunoglobulin G in human proximal tubular epithelial cells.

Proximal tubular epithelial cells (PTECs) have innate immune characteristics, and produce proinflammatory factors, chemokines and complement components that drive epithelial­mesenchymal transition (EMT). Our previous studies revealed that human mesangial cells and podocytes were able to synthesize and secrete immunoglobulin (Ig)A and IgG, respectively. The aim of the present study was to evaluate the expression of Igs in PTECs. Firstly, IgG was detected in the cytoplasm, the cell membrane and the lumen of PTECs in the normal renal cortex by immunohistochemistry. Secondly, Igγ gene transcription and V(D)J recombination were detected in single PTECs by nested PCR and Sanger sequencing. Thirdly, Igγ, Igκ and Igλ were clearly detected in an immortalized PTEC line (HK­2) by immunostaining and western blotting, in which RP215 (an antibody that predominantly binds to non­B cell­derived IgG) was used. In addition, Igγ, Igκ and Igλ gene transcripts, conservative V(D)J recombination in the Igγ variable region, recombination activating gene 1/2 and activation­induced cytidine deaminase were all detected in HK­2 cells. These data suggested that PTECs may express IgG in a similar manner to B cells. Furthermore, IgG expression was upregulated by TGF­ß1 and may be involved in EMT.

A Role for Human Renal Tubular Epithelial Cells in Direct Allo-Recognition by CD4+ T-Cells and the Effect of Ischemia-Reperfusion.

Direct allorecognition is the earliest and most potent immune response against a kidney allograft. Currently, it is thought that passenger donor professional antigen-presenting cells (APCs) are responsible. Further, many studies support that graft ischemia-reperfusion injury increases the probability of acute rejection. We evaluated the possible role of primary human proximal renal tubular epithelial cells (RPTECs) in direct allorecognition by CD4+ T-cells and the effect of anoxia-reoxygenation. In cell culture, we detected that RPTECs express all the required molecules for CD4+ T-cell activation (HLA-DR, CD80, and ICAM-1). Anoxia-reoxygenation decreased HLA-DR and CD80 but increased ICAM-1. Following this, RPTECs were co-cultured with alloreactive CD4+ T-cells. In T-cells, zeta chain phosphorylation and c-Myc increased, indicating activation of T-cell receptor and co-stimulation signal transduction pathways, respectively. T-cell proliferation assessed with bromodeoxyuridine assay and with the marker Ki-67 increased. Previous culture of RPTECs under anoxia raised all the above parameters in T-cells. FOXP3 remained unaffected in all cases, signifying that proliferating T-cells were not differentiated towards a regulatory phenotype. Our results support that direct allorecognition may be mediated by RPTECs even in the absence of donor-derived professional APCs. Also, ischemia-reperfusion injury of the graft may enhance the above capacity of RPTECs, increasing the possibility of acute rejection.

Role and expression of non-classical human leukocyte antigen-G in renal transplanted allografts.

BACKGROUND: The non-classical class I molecule human leukocyte antigen-G (HLA-G) has great potential to modulate the immune response. However, the mechanism underlying HLA-G induction remains unknown. Therefore, this study aimed to determine the factors that induce HLA-G expression on proximal tubular epithelial cells (pTECs) in renal transplanted allografts in vivo and in vitro. METHODS: This study included 40 adult Japanese patients with renal allografts (35 and five patients with kidneys from living and deceased donors, respectively) who survived for at least 1 year. We evaluated HLA-G1/5 expression using an immunofluorescence method and investigated the induction of HLA-G expression in primary cultured human pTECs by cytokines and immunosuppressants. RESULTS: The HLA-G expression was identified in the perinuclear region or on the basement membrane of pTECs of renal biopsy tissue in 12 (30%) of 40 patients at 2-4 weeks and at 1 year following transplantation. A reduction of 30% in the estimated glomerular filtration rate was lower in the HLA-G-positive group than that of the negative group (p = 0.016). Cox proportional hazard models also demonstrated that HLA-G1/5 expression on pTECs was an independent predictor of improved renal allograft function (hazard ratio, 0.189; 95% CI 0.041-0.850, p = 0.030). Interferon-beta was the most powerful inducer of HLA-G expression in vitro, whereas the immunosuppressants everolimus, tacrolimus, cyclosporin, and dexamethasone did not induce any expression. CONCLUSION: Unlike immunosuppressants, acquired HLA-G expression might confer long-term renal preservation effects in renal transplanted allografts.

Role of collectin-11 in innate defence against uropathogenic Escherichia coli infection.

Classical collectins (surfactant protein A and D) play a significant role in innate immunity and host defence in uropathogenic Escherichia coli (UPEC)-induced urinary tract infection (UTI). However, the functions of collectin-11 (CL-11) with respect to UPEC and UTI remain largely unexplored. This study aimed to investigate the effect of CL-11 on UPEC and its role in UTI. We further examined its modulatory effect on inflammatory reactions in proximal tubular epithelial cells (PTECs). The present study provides evidence for the effect of CL-11 on the growth, agglutination, binding, epithelial adhesion and invasion of UPEC. We found increased basal levels of phosphorylated p38 MAPK and human cytokine homologue (keratinocyte-derived chemokine) expression in CL-11 knockdown PTECs. Furthermore, signal regulatory protein α blockade reversed the increased basal levels of inflammation associated with CL-11 knockdown in PTECs. Additionally, CL-11 knockdown effectively inhibited UPEC-induced p38 MAPK phosphorylation and cytokine production in PTECs. These were further inhibited by CD91 blockade. We conclude that CL-11 functions as a mediator of innate immunity via direct antibacterial roles as well as dual modulatory roles in UPEC-induced inflammatory responses during UTI. Thus, the study findings suggest a possible function for CL-11 in defence against UTI.

Single-cell RNA sequencing confirms IgG transcription and limited diversity of VHDJH rearrangements in proximal tubular epithelial cells.

Increasing evidence has confirmed that immunoglobulins (Igs) can be expressed in non-B cells. Our previous work demonstrated that mesangial cells and podocytes express IgA and IgG, respectively. The aim of this work was to reveal whether proximal tubular epithelial cells (PTECs) express Igs. High-throughput single-cell RNA sequencing (scRNA-seq) detected Igs in a small number of PTECs, and then we combined nested PCR with Sanger sequencing to detect the transcripts and characterize the repertoires of Igs in PTECs. We sorted PTECs from the normal renal cortex of two patients with renal cancer by FACS and further confirmed their identify by LRP2 gene expression. Only the transcripts of the IgG heavy chain were successfully amplified in 91/111 single PTECs. We cloned and sequenced 469 VHDJH transcripts from 91 single PTECs and found that PTEC-derived IgG exhibited classic VHDJH rearrangements with nucleotide additions at the junctions and somatic hypermutations. Compared with B cell-derived IgG, PTEC-derived IgG displayed less diversity of VHDJH rearrangements, predominant VH1-24/DH2-15/JH4 sequences, biased VH1 usage, centralized VH gene segment location at the 3' end of the genome and non-Gaussian distribution of the CDR3 length. These results demonstrate that PTECs can express a distinct IgG repertoire that may have implications for their role in the renal tubular epithelial-mesenchymal transition.

Complete remission of nephrotic syndrome in a young woman with anti-LRP2 nephropathy after immunosuppressive therapy.

BACKGROUND: Anti-low density lipoprotein receptor-related protein 2 (LRP2) nephropathy/anti-brush border antibody (ABBA) disease is a disorder characterized by acute tubulointerstitial injury associated with circulating antibodies to kidney proximal tubular brush border protein LRP2/megalin. Patients are typically elderly and present with acute kidney injury and subnephrotic proteinuria. They progress to end-stage renal disease with poor response to immunosuppressive therapies. CASE PRESENTATION: We report a case of a 29-year-old Chinese woman, who presented with nephrotic syndrome with normal kidney function. Kidney biopsy showed no obvious tubular injury or interstitial inflammation. Positive immunoglobulin G (IgG) staining was revealed along the brush border of proximal tubular cells. Anti-LRP2 antibody was identified in serum, consistent with a diagnosis of anti-LRP2 nephropathy. The patient achieved complete remission after receiving prednisone and cyclophosphamide. CONCLUSIONS: Anti-LRP2 nephropathy can also present as nephrotic syndrome in young patients and complete remission from nephrotic syndrome may be achieved after immunosuppressive therapy.

Light chain proximal tubulopathy with cast nephropathy in monoclonal gammopathy of renal significance.

Kidney tubular disorders due to monoclonal immunoglobulin light chains are common manifestations of B-cell neoplasm. Cast nephropathy (CN) is the most frequent type of these disorders and may present with acute kidney injury (AKI) due to the presence of excess light chains in the distal tubules. Light chain proximal tubulopathy (LCPT) is an uncommon form of renal disease and may present as Fanconi syndrome due to proximal tubular cell damage by intracellular deposition of light chains. The concomitant disorder of both CN and LCPT is rare given the inherent differences in the biochemical properties of the immunoglobulin light chains of each disorder. We report a 64-year-old man who presented with AKI and Fanconi syndrome who was discovered to have both CN and LCPT due to the underlying disorder of monoclonal gammopathy of renal significance and who has responded favourably with conventional chemotherapy. We also review the existing literature on this interesting subject.

Clinicopathological characteristics of light chain proximal tubulopathy in Korean patients and the diagnostic usefulness of immunohistochemical staining for immunoglobulin light chain.

BACKGROUND: Light chain proximal tubulopathy (LCPT) is a rare paraproteinemic renal disease that has been mostly reported in Western patients. LCPT is characterized by the accumulation of immunoglobulin (Ig)-light chain (LC) in the proximal tubule. Immunohistochemical staining for Ig-LC has not been investigated in the context of LCPT. We reported the clinicopathological characteristics and Ig-LC immunoexpression of patients with LCPT for the first time in Korea. METHODS: We reviewed the clinicopathological findings of 5 Korean patients diagnosed with LCPT between 2016 and 2018. In addition, immunohistochemical staining for κ-LC and λ-LC was conducted on paraffin-embedded tissues. RESULTS: The median age was 63 years, and the male-to-female ratio was 3:2. The primary renal manifestations were either azotemia or tubular proteinuria. All patients were diagnosed with multiple myeloma with monoclonal κ-LC (#1-2) or λ-LC (#3-5) in the serum and urine. Kidney biopsies revealed diverse and subtle alterations of the proximal tubule, including crystallization, vacuolization, and/or swelling. Electron microscopy revealed crystals in patients #1-2 and non-crystalline particles within numerous/large/dysmorphic lysosomes in patients #3-5. Ig-LC restriction was demonstrated in the proximal tubule as κ-type in patients #1-2 and as λ-type in patients #3-5 by immunohistochemistry and immunofluorescence. Immunohistochemical staining showed diffuse positivity to κ- and λ-LC, although immunofluorescent staining for κ-LC was focal and weak. LCPT has diverse clinicopathological characteristics and subtle morphological alterations, which necessitate ancillary tests for diagnosis. CONCLUSIONS: We introduced immunohistochemical staining for Ig-LC as a useful tool for the diagnosis of LCPT, especially in the case of κ-type crystals.

TCR+CD4-CD8- (double negative) T cells protect from cisplatin-induced renal epithelial cell apoptosis and acute kidney injury.

Acute kidney injury (AKI) due to cisplatin is a significant problem that limits its use as an effective chemotherapeutic agent. T cell receptor+CD4-CD8- double negative (DN) T cells constitute the major T cell population in the human and mouse kidney, express programmed cell death protein (PD)-1, and protect from ischemic AKI. However, the pathophysiological roles of DN T cells in cisplatin-induced AKI is unknown. In this study, wild-type mice were treated with cisplatin (30 mg/kg) or vehicle, and the effects on kidney DN T cell numbers and function were measured. In vitro experiments evaluated effects of kidney DN T cells on cisplatin-induced apoptosis and PD ligand 1 (PD-L1) in renal epithelial cells. Adoptive transfer experiments assessed the therapeutic potential of DN T cells during cisplatin-induced AKI. Our results show that kidney DN T cell population increased at 24 h and declined by 72 h after cisplatin treatment. Cisplatin treatment increased kidney DN T cell proliferation, apoptosis, CD69, and IL-10 expression, whereas CD62L, CD44, IL-17A, interferon-γ, and TNF-α were downregulated. Cisplatin treatment decreased both PD-1 and natural killer 1.1 subsets of kidney DN T cells with a pronounced effect on the PD-1 subset. In vitro kidney DN T cell coculture decreased cisplatin-induced apoptosis in kidney proximal tubular epithelial cells, increased Bcl-2, and decreased cleaved caspase 3 expression. Cisplatin-induced expression of PD ligand 1 was reduced in proximal tubular epithelial cells cocultured with DN T cells. Adoptive transfer of DN T cells attenuated kidney dysfunction and structural damage from cisplatin-induced AKI. These results demonstrate that kidney DN T cells respond rapidly and play a protective role during cisplatin-induced AKI.

Impact of aging on transition of acute kidney injury to chronic kidney disease.

Acute kidney injury (AKI) increases the risk of end stage renal disease among the elderly, but the precise underlying mechanism is unknown. We investigated the effects of aging on AKI-to-chronic kidney disease (CKD) transition, focusing on renal inflammation. Aged and young C57BL/6 mice were subjected to bilateral ischemia-reperfusion injury (IRI). Baseline proinflammatory cytokine levels of kidneys were elevated in aged mice. After IRI, aged mice also showed persistent M1 dominant inflammation, with increased proinflammatory cytokines during the recovery phase. Persistent M1 inflammation was associated with blunted activation of CSF-1/IRF4 signal for M1/M2 polarization, but in vitro macrophage polarization with cytokine stimulation was not different between young and aged mononuclear cells. The tubular expressions of cell cycle arrest markers increased in aged mice during recovery phase, and in vitro transwell experiments showed that mononuclear cells or M1 macrophages co-cultured with arrested proximal tubular cells at G1 phase significantly impaired M2 polarization, suggesting that prolonged G1 arrest might be involved in persistent M1 inflammation in aged mice. Finally, M1 dominant inflammation in aged mice resulted in fibrosis progression. Our data show that impaired M2 polarization partially driven by senescent tubule cells with cell-cycle arrest may lead to an accelerated progression to CKD in the elderly.

Tubular Injury and Dendritic Cell Activation Are Integral Components of Light Chain-Associated Acute Tubulointerstitial Nephritis.

CONTEXT.­: Light chain-associated acute tubulointerstitial nephritis (LC-ATIN) is a variant of light chain proximal tubulopathy (LCPT). It is characterized by interstitial inflammation with tubulitis and deposition of monoclonal light chains in the tubulointerstitium. LC-ATIN is a rather poorly recognized pattern of LCPT and not much is known about this entity. OBJECTIVE.­: To determine the clinicopathologic features of patients with LC-ATIN and investigate the proximal tubular injury and mechanism of interstitial inflammation in LC-ATIN. DESIGN.­: A total of 38 cases of LC-ATIN were identified from the archives of 5043 renal biopsy specimens. In all cases, routine light microscopic examination, immunofluorescence, and electron microscopic examination were performed. In selected cases, immunofluorescent staining of dendritic cells and immunohistochemical staining for 4 tubular injury markers-KIM-1, p53, bcl-2, and Ki-67-were performed. RESULTS.­: A characteristic finding in LC-ATIN cases was immunofluorescence staining of monoclonal light chains along tubular basement membranes in linear fashion and inside proximal tubular cells with a granular pattern. No monoclonal light chains were present in glomerular or vascular compartments confirmed with immunofluorescence, electron microscopy, and ultrastructural gold labeling. Ten of 15 LC-ATIN cases (67%) were concurrently positive for the 4 tubular injury markers. Dendritic cells were identified within the tubulointerstitium in the renal biopsy specimens, interacting with surrounding tubules with light-chain deposits and inflammatory cells. CONCLUSIONS.­: Significant proximal tubular injury occurs associated with LC-ATIN, and the monoclonal light chains accumulated in proximal tubular cells contribute to the injury. Dendritic cells are involved in the pathogenesis of interstitial inflammation in LC-ATIN.

FKN Facilitates HK-2 Cell EMT and Tubulointerstitial Lesions via the Wnt/ß-Catenin Pathway in a Murine Model of Lupus Nephritis.

Fractalkine (FKN), also known as chemokine (C-X3-C motif) ligand 1, constitutes an intriguing chemokine with a documented role in the development of numerous inflammatory diseases including autoimmune disease. Specifically, it has been reported that FKN is involved in the disease progression of lupus nephritis (LN). The epithelial-mesenchymal transition (EMT) plays a significant role in the formation of tubulointerstitial lesions (TIL), which are increasingly recognized as a hallmark of tissue fibrogenesis after injury. However, the correlation between FKN and EMT or TIL in LN has not been determined. To investigate the potential role of FKN in EMT and TIL, MRL lymphoproliferation (MRL/lpr) strain mice were treated with an anti-FKN antibody, recombinant-FKN chemokine domain, or isotype antibody. Our results revealed that treatment with the anti-FKN antibody improved EMT, TIL, and renal function in MRL/lpr mice, along with inhibiting activation of the Wnt/ß-catenin signaling pathway. In contrast, administration of the recombinant-FKN chemokine domain had the opposite effect. Furthermore, to further explore the roles of FKN in EMT, we assessed the levels of EMT markers in FKN-depleted or overexpressing human proximal tubule epithelial HK-2 cells. Our results provide the first evidence that the E-cadherin level was upregulated, whereas α-SMA and vimentin expression was downregulated in FKN-depleted HK-2 cells. In contrast, overexpression of FKN in HK-2 cells enhanced EMT. In addition, inhibition of the Wnt/ß-catenin pathway by XAV939 negated the effect of FKN overexpression, whereas activation of the Wnt/ß-catenin pathway by Ang II impaired the effect of the FKN knockout on EMT in HK-2 cells. Together, our data indicate that FKN plays essential roles in the EMT progression and development of TIL in MRL/lpr mice, most likely through activation of the Wnt/ß-catenin signaling pathway.

Interaction between galectin-3 and cystinosin uncovers a pathogenic role of inflammation in kidney involvement of cystinosis.

Inflammation is involved in the pathogenesis of many disorders. However, the underlying mechanisms are often unknown. Here, we test whether cystinosin, the protein involved in cystinosis, is a critical regulator of galectin-3, a member of the ß-galactosidase binding protein family, during inflammation. Cystinosis is a lysosomal storage disorder and, despite ubiquitous expression of cystinosin, the kidney is the primary organ impacted by the disease. Cystinosin was found to enhance lysosomal localization and degradation of galectin-3. In Ctns-/- mice, a mouse model of cystinosis, galectin-3 is overexpressed in the kidney. The absence of galectin-3 in cystinotic mice ameliorates pathologic renal function and structure and decreases macrophage/monocyte infiltration in the kidney of the Ctns-/-Gal3-/- mice compared to Ctns-/- mice. These data strongly suggest that galectin-3 mediates inflammation involved in kidney disease progression in cystinosis. Furthermore, galectin-3 was found to interact with the pro-inflammatory cytokine Monocyte Chemoattractant Protein-1, which stimulates the recruitment of monocytes/macrophages, and proved to be significantly increased in the serum of Ctns-/- mice and also patients with cystinosis. Thus, our findings highlight a new role for cystinosin and galectin-3 interaction in inflammation and provide an additional mechanistic explanation for the kidney disease of cystinosis. This may lead to the identification of new drug targets to delay cystinosis progression.

Renal proximal tubular epithelial cells exert immunomodulatory function by driving inflammatory CD4+ T cell responses.

In immune-mediated glomerular diseases like crescentic glomerulonephritis (cGN), inflammatory CD4+ T cells accumulate within the tubulointerstitial compartment in close contact to proximal and distal tubular epithelial cells and drive renal inflammation and tissue damage. However, whether renal epithelial cell populations play a role in the pathogenesis of cGN by modulating CD4+ T cell responses is less clear. In the present study, we aimed to investigate the potential of renal epithelial cells to function as antigen-presenting cells, thereby stimulating CD4+ T cell responses. Using a FACS-based protocol that allowed comparative analysis of cortical epithelial cell populations, we showed that particularly proximal tubular epithelial cells (PTECs) express molecules linked with antigen-presenting cell function, including major histocompatibility complex class II (MHCII), CD74, CD80, and CD86 in homeostasis and nephrotoxic nephritis, a murine model of cGN. Protein expression was visualized at the PTEC single cell level by imaging flow cytometry. Interestingly, we found inflammation-dependent regulation of epithelium-expressed CD74, CD80, and CD86, whereas MHCII expression was not altered. Antigen-specific stimulation of CD4+ T cells by PTECs in vitro supported CD4+ T cell survival and induced CD4+ T cell activation, proliferation, and inflammatory cytokine production. In patients with antineutrophil cytoplasmic antibody-associated glomerulonephritis, MHCII and CD74 were expressed by both proximal and distal tubules, whereas CD86 was predominantly expressed by proximal tubules. Thus, particularly PTECs have the potential to induce an inflammatory phenotype in CD4+ T cells in vitro, which might also play a role in the pathology of immune-mediated kidney disease.

Lambda Light Chain Non-crystalline Proximal Tubulopathy with IgD Lambda Myeloma.

Light Chain Proximal Tubulopathy (LCPT) is a rare form of paraprotein-related kidney disease in which monoclonal free light chains damage the proximal renal tubular epithelial cells. We herein report the case of a 78-year-old woman who presented with anemia and kidney dysfunction. Serum and urine protein electrophoresis analyses revealed a monoclonal IgD and λ free light chains. Proximal tubular injury and the accumulation of λ light chains were found by kidney biopsy. Electron microscopy revealed no organized structure suggestive of crystals. LCPT was caused by IgD lambda myeloma and bortezomib and dexamethasone therapy led to very good partial response (VGPR) without a worsening of the kidney function.

Activated natural killer T cells in mice induce acute kidney injury with hematuria through possibly common mechanisms shared by human CD56+ T cells.

Although activation of mouse natural killer T (NKT) cells by α-galactosylceramide (α-GalCer) causes failure of multiple organs, including the kidneys, the precise mechanisms underlying kidney injury remain unclear. Here, we showed that α-GalCer-activated mouse NKT cells injured both kidney vascular endothelial cells and tubular epithelial cells in vitro, causing acute kidney injury (AKI) with hematuria in middle-aged mice. The perforin-mediated pathway was mainly involved in glomerular endothelial cell injury, whereas the TNF-α/Fas ligand pathway played an important role in the injury of tubular epithelial cells. Kidney injury in young mice was mild but could be significantly exacerbated if NKT cells were strongly activated by NK cell depletion alone or in combination with IL-12 pretreatment. When stimulated by a combination of IL-2 and IL-12, human CD56+ T cells, a functional counterpart of mouse NKT cells, also damaged both glomerular endothelial cells and tubular epithelial cells, with the former being affected in a perforin-dependent manner. These data suggest that both mouse NKT cells and human CD56+ T cells are integral to the processes that mediate AKI. Targeting CD56+ T cells may, therefore, be a promising approach to treat AKI.

Human plasmacytoid dendritic cells acquire phagocytic capacity by TLR9 ligation in the presence of soluble factors produced by renal epithelial cells.

Plasmacytoid dendritic cells (pDCs) are antigen presenting cells specialized in viral recognition through Toll-like receptor (TLR)7 and TLR9, and produce vast amounts of interferon alpha upon ligation of these TLRs. We had previously demonstrated a strong influx of pDCs in the tubulointerstitium of renal biopsies at the time of acute rejection. However, the role of human pDCs in mediating acute or chronic allograft rejection remains elusive. pDCs are thought to have a limited capacity to ingest apoptotic cells, critical for inducing CD4+ T cell activation via indirect antigen presentation and subsequent activation of antibody producing B cells. Here we tested whether the function of pDCs is affected by their presence within the graft. Maturation and interferon alpha production by pDCs was enhanced when cells were activated in the presence of viable HK2 renal epithelial cells. Importantly, soluble factors produced by cytomegalovirus-infected (primary) epithelial or endothelial cells enhanced pDC activation and induced their capacity to phagocytose apoptotic cells. Phagocytosis was not induced by free virus or soluble factors from non-infected cells. Activated pDCs showed an enhanced CD4+ and CD8+ T cell allostimulatory capacity as well as a potent indirect alloantigen presentation. Granulocyte Macrophage-Colony Stimulating Factor is one of the soluble factors produced by renal epithelial cells that, combined with TLR9 ligation, induced this functional capacity. Thus, pDCs present in the rejecting allograft can contribute to alloimmunity and potentially act as important orchestrators in the manifestation of acute and chronic rejection.