Chemokine receptor (CCR5) expression in human kidneys and in the HIV infected macaque

Collapsing glomerulopathy: unraveling varied pathogeneses

PURPOSE OF REVIEW

Collapsing glomerulopathy presents clinically with nephrotic syndrome and rapid progressive loss of kidney function. Animal models and patient studies have uncovered numerous clinical and genetic conditions associated with collapsing glomerulopathy, as well as putative mechanisms, which will be reviewed here.

RECENT FINDINGS

Collapsing glomerulopathy is classified pathologically as a variant of focal and segmental glomerulosclerosis (FSGS). As such, most research efforts have focused on the causative role of podocyte injury in driving the disease. However, studies have also shown that injury to the glomerular endothelium or interruption of the podocyte-glomerular endothelial cell signaling axis can also cause collapsing glomerulopathy. Furthermore, emerging technologies are now enabling exploration of diverse molecular pathways that can precipitate collapsing glomerulopathy using biopsies from patients with the disease.

SUMMARY

Since its original description in the 1980s, collapsing glomerulopathy has been the subject of intense study, and these efforts have uncovered numerous insights into potential disease mechanisms. Newer technologies will enable profiling of the intra-patient and inter-patient variability in collapsing glomerulopathy mechanisms directly in patient biopsies, which will improve the diagnosis and classification of collapsing glomerulopathy.

Regulatory Noncoding and Predicted Pathogenic Coding Variants of CCR5 Predispose to Severe COVID-19

Genome-wide association studies (GWAS) found locus 3p21.31 associated with severe COVID-19. CCR5 resides at the same locus and, given its known biological role in other infection diseases, we investigated if common noncoding and rare coding variants, affecting CCR5, can predispose to severe COVID-19. We combined single nucleotide polymorphisms (SNPs) that met the suggestive significance level (P ≤ 1 × 10-5) at the 3p21.31 locus in public GWAS datasets (6406 COVID-19 hospitalized patients and 902,088 controls) with gene expression data from 208 lung tissues, Hi-C, and Chip-seq data. Through whole exome sequencing (WES), we explored rare coding variants in 147 severe COVID-19 patients. We identified three SNPs (rs9845542, rs12639314, and rs35951367) associated with severe COVID-19 whose risk alleles correlated with low CCR5 expression in lung tissues. The rs35951367 resided in a CTFC binding site that interacts with CCR5 gene in lung tissues and was confirmed to be associated with severe COVID-19 in two independent datasets. We also identified a rare coding variant (rs34418657) associated with the risk of developing severe COVID-19. Our results suggest a biological role of CCR5 in the progression of COVID-19 as common and rare genetic variants can increase the risk of developing severe COVID-19 by affecting the functions of CCR5.

HIV-associated nephropathy: links, risks and management

Despite the decreased incidence of human immunodeficiency virus (HIV)-associated nephropathy due to the widespread use of combined active antiretroviral therapy, it remains one of the leading causes of end-stage renal disease (ESRD) in HIV-1 seropositive patients. Patients usually present with low CD4 count, high viral load and heavy proteinuria, with the pathologic findings of collapsing focal segmental glomerulosclerosis. Increased susceptibility exists in individuals with African descent, largely due to polymorphism in APOL1 gene. Other clinical risk factors include high viral load and low CD4 count. Advanced kidney disease and nephrotic range proteinuria have been associated with progression to ESRD. Improvement in kidney function has been observed after initiation of combined active antiretroviral therapy. Other treatment options, when clinically indicated, are inhibition of the renin-angiotensin system and corticosteroids. Further routine management approaches for patients with chronic kidney disease should be implemented. In patients with progression to ESRD, kidney transplant should be pursued, provided that viral load control is adequate. Screening for the presence of kidney disease upon detection of HIV-1 seropositivity in high-risk populations is recommended.

Update on current management of chronic kidney disease in patients with HIV infection

The prevalence of HIV-associated chronic kidney disease (CKD) varies geographically and depends on the definition of CKD used, ranging from 4.7% to 38% globally. The incidence, however, has decreased with the use of effective combined antiretroviral therapy (cART). A wide variety of histological patterns are seen in HIV-associated kidney diseases that include glomerular and tubulointerstitial pathology. In resource-rich settings, there has been a plateau in the incidence of end-stage renal disease secondary to HIV-associated nephropathy (HIVAN). However, the prevalence of end-stage renal disease in HIV-positive individuals has risen, mainly due to increased longevity on cART. There is a disparity in the occurrence of HIVAN among HIV-positive individuals such that there is an 18- to 50-fold increased risk of developing kidney disease among HIV-positive individuals of African descent aged between 20 and 64 years and who have a poorer prognosis compared with their European descent counterparts, suggesting that genetic factors play a vital role. Other risk factors include male sex, low CD4 counts, and high viral load. Improvement in renal function has been observed after initiation of cART in patients with HIV-associated CKD. Treatment with an angiotensin-converting enzyme inhibitor/angiotensin receptor blocker is recommended, when clinically indicated in patients with confirmed or suspected HIVAN or clinically significant albuminuria. Other standard management approaches for patients with CKD are recommended. These include addressing other cardiovascular risk factors (appropriate use of statins and aspirin, weight loss, cessation of smoking), avoidance of nephrotoxins, and management of serum bicarbonate and uric acid, anemia, calcium, and phosphate abnormalities. Early diagnosis of kidney disease by screening of HIV-positive individuals for the presence of kidney disease is critical for the optimal management of these patients. Screening for the presence of kidney disease upon detection of HIV infection and annually thereafter in high-risk populations is recommended.

Controversies in the pathogenesis of HIV-associated renal diseases

The two most common HIV-associated renal diseases, HIV-associated nephropathy and HIV immune-complex kidney disease, share the common pathologic finding of hyperplasia within the glomerulus. Podocyte injury is central to the pathogenesis of these diseases; however, the source of the proliferating glomerular epithelial cell remains a topic of debate. Parenchymal injury has been linked to direct infection of renal epithelial cells by HIV-1, although the mechanism of viral entry into this non-lymphoid compartment is unclear. Although transgenic rodent models have provided insight into viral proteins responsible for inducing renal disease, such models have substantial limitations. Rodent HIV-1 models, for instance, cannot replicate all features of immune activation, a process that could have an important role in the pathogenesis of the HIV-associated renal diseases.

Thrombotic microangiopathy and other glomerular disorders in the HIV-infected patient

SUMMARY

Various forms of kidney disease have been related directly to human immunodeficiency virus (HIV) viral infection, including HIV-associated nephropathy (HIVAN), immune complex diseases, and thrombotic microangiopathy (TMA). HIVAN and HIV immune complex glomerulonephritides are the most common HIV-specific nephropathies. HIV-associated TMA, although far less common, remains an important consideration. The diagnosis of TMA in HIV, which has a poorly understood pathogenesis, can be suggested by thrombocytopenia, microangiopathic hemolytic anemia, and acute renal failure, but only definitively diagnosed by kidney biopsy. Not surprisingly, the incidence and prevalence of the HIV-specific entities have declined with the advent of highly active antiretroviral therapy. With this decline, however, other glomerular diseases are of increasing importance in this high-risk population. The differential diagnosis of glomerular disease in an HIV-positive patient is therefore broad. Glomerular diseases seen in this population include classic focal segmental glomerulosclerosis, IgA nephropathy, postinfectious glomerulonephritis, hepatitis B- and C-related glomerulonephritides, and membranous nephropathy. In addition, as the HIV-infected population ages, diabetic and hypertensive nephropathies are likely to become more prevalent. With overlapping presentations of these entities, definitive diagnosis often is difficult, necessitating kidney biopsy. As a consequence of establishing an accurate diagnosis, improved patient outcome can best be accomplished through disease-specific intervention.

Pathogenesis of HIV-associated nephropathy

Human immunodeficiency virus-associated nephropathy (HIVAN) is a leading cause of end-stage renal disease in the HIV-1-seropositive population. HIVAN, which is characterized by heavy proteinuria and a rapid decline in renal function, is caused by infection and subsequent expression of viral genes in renal epithelial cells, although the exact mechanism of viral entry into these cells is unknown. The infected renal epithelium is a distinct compartment that supports the evolution of viral strains that may diverge from those found in the patient's blood. Research using animal models and in vitro studies has shown that vpr and nef are the HIV-1 genes most responsible for inducing the characteristic clinical and histopathologic syndrome of HIVAN. Dysregulation of several host factors, including mediators of inflammation, apoptosis, proliferation, transcription, and cell-cell interactions, are also critical factors in determining whether infection of the renal epithelium will lead to HIVAN. Additional research is required to delineate the mechanisms of HIVAN pathogenesis further so that more effective interventions can be implemented to prevent and treat this disease.

Infection and glomerulonephritis

Glomerular injury, occurring either as primary glomerular disease or as part of a systemic disease process, is usually a result of immune-mediated mechanisms. The morphologic reaction pattern has a diverse spectrum of appearance, ranging from normal by light microscopy in minimal change disease to crescentic forms of glomerulonephritis, with conspicuous disruption of the normal glomerular morphology. The mechanisms of glomerular immune deposit formation include trapping of circulating antigen-antibody complexes and the in situ formation of immune complexes within the glomerulus. While the majority of postinfectious immune-complex-mediated glomerulonephritides are believed to result from the deposition of circulating antigen-antibody complexes, preformed outside of the kidney and secondarily deposited in the kidney, the notion of forming in situ antigen-antibody complexes to either planted antigens or to integral structural components of the glomerulus, through "cross-reacting" autoimmune reactions, is gaining popularity in a variety of forms of glomerulonephritides. Patients with HIV infection may develop a spectrum of renal pathology, the glomerular manifestations of which include both antigen-antibody complex and nonimmune-complex-mediated pathogenetic mechanisms. Similarly, patients with Streptococcal infections, Hepatitis B virus, or Hepatitis C virus infection may develop a spectrum of glomerulonephritides, which are predominantly immune-complex-mediated. Therapy for glomerular diseases due to HIV, hepatitis B, or C virus infections remains a challenge.

DEC-205-mediated internalization of HIV-1 results in the establishment of silent infection in renal tubular cells

HIV-1 infection of renal cells has been proposed to play a role in HIV-1-associated nephropathy. Renal biopsy data further suggest that renal tubular cells may serve as reservoir for HIV-1. The mechanism by which HIV-1 enters these cells has not been identified. Renal tubular cells do not express any of the known HIV-1 receptors, and our results confirmed lack of the expression of CD4, CCR5, CXCR4, DC-SIGN, or mannose receptors in tubular cells. The aim of this study, therefore, was to determine the mechanism that enables viral entry into renal tubular cells. An in vitro model was used to study the HIV-1 infection of human kidney tubular (HK2) cells and to identify the receptor that enables the virus to enter these cells. Results of these studies demonstrate that the C-type lectin DEC-205 acts as an HIV-1 receptor in HK2 cells. Interaction of HIV-1 with DEC-205 results in the internalization of the virus and establishment of a nonproductive infection. HIV-1-specific strong-stop DNA is detected in the infected HK2 cells for at least 7 d, and the virus can be transmitted in trans to sensitive target cells. HIV-1 entry is blocked by pretreatment with specific anti-DEC-205 antibody. Moreover, expression of DEC-205 in cells that lack the DEC-205 receptors renders them susceptible to HIV-1 infection. These findings suggest that DEC-205 acts as an HIV-1 receptor that mediates internalization of the virus into renal tubular cells, from which the virus can be rescued and disseminated by encountering immune cells.

The CC chemokine receptor 5 is important in control of parasite replication and acute cardiac inflammation following infection with Trypanosoma cruzi

Infection of susceptible mice with the Colombiana strain of Trypanosoma cruzi results in an orchestrated expression of chemokines and chemokine receptors within the heart that coincides with parasite burden and cellular infiltration. CC chemokine receptor 5 (CCR5) is prominently expressed during both acute and chronic disease, suggesting a role in regulating leukocyte trafficking and accumulation within the heart following T. cruzi infection. To better understand the functional role of CCR5 and its ligands with regard to both host defense and/or disease, CCR5(-/-) mice were infected with T. cruzi, and the disease severity was evaluated. Infected CCR5(-/-) mice develop significantly higher levels of parasitemia (P < or = 0.05) and cardiac parasitism (P < or = 0.01) during acute infection that correlated with reduced survival. Further, we show that CCR5 is essential for directing the migration of macrophages and T cells to the heart early in acute infection with T. cruzi. In addition, data are provided demonstrating that CCR5 does not play an essential role in maintaining inflammation in the heart during chronic infection. Collectively, these studies clearly demonstrate that CCR5 contributes to the control of parasite replication and the development of a protective immune response during acute infection but does not ultimately participate in maintaining a chronic inflammatory response within the heart.

Fusion of HIV-1 envelope-expressing cells to human glomerular endothelial cells through an CXCR4-mediated mechanism

A central question in the pathogenesis of HIV-associated thrombotic microangiopathic (HIV-TMA) lesions is whether the HIV-1 envelope glycoprotein (HIV-1 Env) can interact directly with human glomerular endothelial cells (HGECs) through specific HIV-1 co-receptors. The goal of this study was to determine whether cultured primary HGECs express significant levels of the major HIV-1 co-receptors CD4, CXCR4, and/or CCR5 to allow fusion interactions with HIV-1. The expression of CD4, CXCR-4 and CCR-5 was assessed in cultured HGECs by reverse transcriptase-polymerase chain reaction (RT-PCR) and flow cytometry using specific antibodies. The HIV-1 Env-mediated membrane fusion of target glomerular cells was evaluated by a fluorescent dye transfer-based cell-cell fusion microscopic method. HGECs express CXCR4 mRNA and protein as determined by RT-PCR and immunostaining with phycoerythrin-conjugated anti-CXCR4 Mab 12G5. CD4 and CCR5 were not detected in HGECs, either by RT-PCR or by surface immunostaining with specific antibodies. Incubation of HGECs with cells expressing a CD4-independent envelope strain (HIV-1IIIB-8x) and the CD4-dependent envelope strain (HIV-1IIIB) resulted in transfer of fluorescent dyes of approximately 20% after 8-16 h incubation at 37 degrees C. Incubation in the presence of inhibitors (C34, which blocks six-helix bundle formation, and AMD3100, which interacts with CXCR4) reduced dye transfer by 60%-80%, confirming that the dye transfer was specific with respect to gp120-gp41-mediated fusion. Cultured primary HGECs express CXCR4 but not CD4 or CCR5. The ability of HGECs to promote fusion by a CD4-independent HIV-1 envelope glycoprotein suggests that these cells may become a potential direct target of certain HIV-1 isolates.

A 20-year history of childhood HIV-associated nephropathy

In 1984, physicians in New York and Miami reported HIV-infected adult patients with heavy proteinuria and rapid progression to end-stage renal disease. These patients showed large edematous kidneys with a combination of focal segmental glomerulosclerosis (FSGS) and tubulointerstitial lesions. This renal syndrome, named HIV-associated nephropathy (HIVAN), was found predominantly in African Americans. Subsequent studies confirmed the presence of HIVAN in children, who frequently develop nephrotic syndrome in association with FSGS and/or mesangial hyperplasia with microcystic tubular dilatation. Since then, substantial progress has been made in our understanding of the etiology and pathogenesis of HIVAN. This article reviews 20 years of research into the pathogenesis of HIVAN and discusses how these concepts could be applied to the treatment of children with HIVAN. HIV-1 infection plays a direct role in the pathogenesis of childhood HIVAN, at least partially by affecting the growth and differentiation of glomerular and tubular epithelial cells and enhancing the renal recruitment of infiltrating mononuclear cells and cytokines. An up-regulation of renal heparan sulfate proteoglycans seems to play a relevant role in this process, by increasing the recruitment of heparin-binding growth factors (i.e., FGF-2), chemokines, HIV-infected cells, and viral proteins (i.e., gp120, Tat). These changes enhance the infectivity of HIV-1 in the kidney and induce injury and proliferation of intrinsic renal cells. Highly active anti-retroviral therapy (HAART) appears to be the most promising treatment to prevent the progression of childhood HIVAN. Hopefully, in the near future, better education, prevention, and treatment programs will lead to the eradication of this fatal childhood disease.

Focal glomerulosclerosis in proviral and c-fms transgenic mice links Vpr expression to HIV-associated nephropathy

Clinical and morphologic features of human immunodeficiency virus (HIV)-associated nephropathy (HIVAN), such as proteinuria, sclerosing glomerulopathy, tubular degeneration, and interstitial disease, have been modeled in mice bearing an HIV proviral transgene rendered noninfectious through a deletion in gag/pol. Exploring the genetic basis of HIVAN, HIV transgenic mice bearing mutations in either or both of the accessory genes nef and vpr were created. Proteinuria and focal glomerulosclerosis (FGS) only developed in mice with an intact vpr gene. Transgenic mice bearing a simplified proviral DNA (encoding only Tat and Vpr) developed renal disease characterized by FGS in which Vpr protein was localized to glomerular and tubular epithelia by immunohistochemistry. The dual transgenic progeny of HIV[Tat/Vpr] mice bred to HIV[DeltaVpr] proviral transgenic mice displayed a more severe nephropathy with no apparent increase in Vpr expression, implying that multiple viral genes contribute to HIVAN. However, the unique contribution of macrophage-specific Vpr expression in the development of glomerular disease was underscored by the induction of FGS in multiple murine lines bearing a c-fms/vpr transgene.

Chemokines and chemokine receptors in renal pathology

PURPOSE OF REVIEW

Chemokines are members of the largest group of chemotactic cytokines, and were the first shown to be able to engage specific subpopulations of inflammatory cells. Accordingly, our expanding knowledge in chemokine biology has enlarged our understanding of inflammatory cell interactions, lymphopoesis, specificity of cell recruitment, and a variety of human diseases. This review covers recent developments on chemokines in renal diseases.

RECENT FINDINGS

Intrinsic renal cells are capable of chemokine expression in vitro and in vivo, and the involved induction pathways are becoming increasingly defined. Differential chemokine expression during the time course of disease, followed by an infiltration of cells expressing the corresponding receptors has been described in animal models. Therapeutic efficacy of chemokine blockade has been demonstrated in a variety of disease models, including progressive interstitial fibrosis. Chemokine receptors are differentially expressed and localized to specific parenchymal compartments in human renal diseases, as revealed by studies of renal biopsies, and some functional roles of specific chemokine/receptor interactions can be deduced through the correlation of patterns of expression, genetic variations and disease courses.

SUMMARY

Chemokines play an important role in renal inflammation. Although the treatment of patients with renal diseases using chemokine receptor blocking agents has not yet reached clinical practice, a recent body of data indicates that human renal disease might be amenable to such approaches.

Post-transplant renal tubulitis: the recruitment, differentiation and persistence of intra-epithelial T cells

Tubulitis is used by the Banff protocol as a major criterion to grade acute renal allograft rejection. This review integrates results from in vitro and in vivo studies to develop a chronological model to explain the development and functions of tubular inflammation during the rejection process. Proteoglycan-immobilized chemokines are the primary motivators for the vectorial recruitment of specific immune cell populations from the blood, through the endothelium and interstitial tissues to the renal tubules. After penetration of the basement membrane, T cells encounter TGF-beta that can induce expression of the alphaEbeta7 integrin on proliferating cells. This allows adhesion to E-cadherin on the baso-lateral surfaces of tubular epithelial cells and provides an explanation for the epithelial-specific cytotoxicity observed during acute rejection. Tubular epithelium is also a rich source of IL-15 that can stimulate IL-15 receptor-expressing intratubular CD8+ T cells. This anti-apoptotic microenvironment may explain the long-term persistence of cycling T cells within intact tubules after episodes of acute rejection. These memory-like T cells may have local immunoregulatory properties, including the production of additional TGF-beta, but could also modify normal tubular homeostasis resulting in epithelial to mesenchymal transdifferentiation, tubulointerstitial fibrosis and, ultimately, graft failure.

The challenge of viral reservoirs in HIV-1 infection

A viral reservoir is a cell type or anatomical site in association with which a replication-competent form of the virus accumulates and persists with more stable kinetic properties than the main pool of actively replicating virus. This article reviews several cell types and anatomical sites proposed as potential reservoirs for HIV-1. It is now clear that HIV-1 persists in a small reservoir of latently infected resting memory CD4(+) T cells, which shows minimal decay even in patients on highly active antiretroviral therapy (HAART). The persistence of virus in this reservoir is consistent with the biology of these cells and the long-term persistence of immunologic memory. The viral replication that continues in patients on suppressive HAART may also contribute to the stability of this reservoir. There may be other reservoirs, but the latent reservoir in resting CD4(+) T cells appears to be sufficient to guarantee lifetime persistence of HIV-1 in the majority of patients on current HAART regimens, and unless new approaches are developed, eradication will not be possible. The clinical implications of this and other HIV-1 reservoirs are discussed.

Systemic and intestinal immune responses to HIV-2287 infection in Macaca nemestrina

Nonhuman primate models of human AIDS have been used successfully to evaluate candidate vaccines and infection intervention therapies. Successes of pathogenicity studies in primate models have been limited because of the varied infection outcomes and characteristic low number of study animals. The acutely pathogenic HIV-2(287)--Macaca nemestrina model has shown promise both in antiviral drug evaluation and in pathogenicity studies. Here we describe virus replication, spread, and host responses during the first 28 days of HIV-2(287) infection. Focusing on 18 macaques from a larger 27-macaque study, we report changing virus loads, CD4(+) cell depletions, and antibody responses both systemically and in the mucosa of the small intestine. After intravenous inoculation, blood and intestinal tissue were collected from pairs of macaques at 12 hr and 1, 2, 4, 6, 10, 14, 21, and 28 days postinfection. Specimens were examined for evidence of infection by quantitative cultures, in situ hybridization, lymphocyte subset monitoring, and antibody production. The data were presented serially as though all samples were collected from a single macaque. The highest blood virus loads were detected between days 10 and 14 and subsequently decreased through day 28. This coincided with a significant increase in ileum mucosa virus loads on day 10, which became undetectable by day 28. The lowest levels of CD4(+) cells were observed on days 21 and 28 in blood and ileum mucosa. CD4(+):CD8(+) cell ratios in blood and ileum dropped dramatically after day 10 to lowest levels by day 28. Intestinal virus loads were inversely correlated with CD4(+) cell and virus-specific antibody levels in the ileum after day 6. These results underscore the suitability of this model for pathogenicity studies as well as the importance of the intestinal lymphoid tissues as an initial site of virus replication and cell destruction during the acute, asymptomatic stage of AIDS development.

CCR1-specific non-peptide antagonist: efficacy in a rabbit allograft rejection model

The classic signs of acute cellular rejection during organ transplantation include the infiltration of mononuclear cells into the interstitium. This recruitment of leukocytes into the transplanted tissue is promoted by chemokines like RANTES. Since RANTES is a potent agonist for the CC chemokine receptor CCR1, we examined whether the CCR1 antagonist BX 471 was efficacious in a rabbit kidney transplant rejection model. BX 471 was able to compete with high affinity with the CCR1 ligands MIP-1alpha and RANTES for binding to HEK 293 cells expressing rabbit CCR1. BX 471 was a competitive antagonist of rabbit CCR1 in Ca(2+) flux studies. Two separate studies in which animals were subcutaneously implanted with slow release pellets of BX 471 demonstrated that animals implanted with BX 471 had increased survival compared with untreated controls or animals implanted with placebo. The mean survival time for the placebo group was 12.33+/-1.7 days. The animals in the BX 471 treated group had mean survival times of 16.9+/-2.1 and 16.0+/-1.7 days, respectively, for the two studies. Analysis of the combined data by Student t-test gave a P value of 0.03 that is significant at the 0.05 level. In addition, there was a marked reduction in the urea and creatinine levels in the BX 471 treated animals compared with the control and placebo groups in both studies. Finally, pathologic analysis of the kidneys in the rabbit renal transplantation model from animals in the different groups showed that BX 471 was similar to cyclosporin in its ability to prevent extensive infarction of transplanted kidneys. Based on the data from these studies, BX 471 shows clear efficacy at the single dose tested compared with animals treated with placebo.

Depletion of CCR5-expressing cells with bispecific antibodies and chemokine toxins: a new strategy in the treatment of chronic inflammatory diseases and HIV

The chemokine receptor CCR5 is expressed on the majority of T cells and monocytes in the inflammatory infiltrate of diseases such as rheumatoid arthritis, renal diseases, and multiple sclerosis. In contrast, little expression of CCR5 is found on peripheral blood leukocytes. A specific depletion of CCR5(+) cells could therefore be a useful strategy to reduce the cellular infiltrate in chronic inflammations. Moreover, CCR5 is the major coreceptor for M-tropic HIV-1 strains. Depletion of CCR5(+) leukocytes may help to eliminate cells latently infected with HIV-1. We designed two constructs that specifically destroy chemokine receptor-positive cells. The first construct, a bispecific Ab, binds simultaneously to CCR5 and CD3. Thereby it redirects CD3(+) T cells against CCR5(+) target cells. The Ab specifically depletes CCR5(+) T cells and monocytes, but is inactive against cells that do not express CCR5. Furthermore, ex vivo the bispecific Ab eliminated >95% of CCR5(+) monocytes and T cells from the synovial fluid of patients with arthritis. Also, we designed a fusion protein of the chemokine RANTES and a truncated version of Pseudomonas. exotoxin A. The fusion protein binds to CCR5 and down-modulates the receptor from the cell surface. The chemokine toxin completely destroyed CCR5(+) Chinese hamster ovary cells at a concentration of 10 nM, whereas no cytotoxic effect was detectable against CCR5(-) Chinese hamster ovary cells. Both constructs efficiently deplete CCR5-positive cells, appear as useful agents in the treatment of chronic inflammatory diseases, and may help to eradicate HIV-1 by increasing the turnover of latently infected cells.

Expression of the chemokine monocyte chemoattractant protein-1 and its receptor chemokine receptor 2 in human crescentic glomerulonephritis

Crescents are morphologic manifestations of severe glomerular injury. Several chemokines and their receptors have been demonstrated to be involved in animal models of crescentic glomerulonephritis (cGN) and are potential targets for therapeutic interventions. Therefore, the expression of monocyte chemoattractant protein-1 (MCP-1), its receptor chemokine receptor 2B (CCR2B), and CCR5 in human cGN was studied. MCP-1 and CCR2B mRNA expression was evaluated, by in situ hybridization, in serial sections of 23 renal biopsies from patients with cGN. T cells, macrophages, and CCR5-expressing cells were examined by immunohistochemical analysis. MCP-1 mRNA was expressed by cells in crescents, parietal epithelium, and tubular epithelium, as well as by infiltrating leukocytes in the tubulointerstitium. The expression of CCR2B mRNA was observed in cells in glomeruli and crescents and in infiltrating leukocytes in the tubulointerstitium. CCR2B mRNA expression could not be clearly localized to intrinsic renal cells; evidence that most of the CCR2B-expressing cells were leukocytes is provided. CD3-positive T cells formed the major part of the interstitial cell infiltrates but were rare within the glomerular tufts. CD68-positive macrophages constituted a major population of infiltrating cells in crescents and contributed significantly to the interstitial infiltrates. The number of glomerular macrophages was associated with the number of MCP-1- and CCR2B-positive glomerular cells. Expression of CCR2B was significantly correlated with interstitial CD3-positive T cells. CCR5 expression was restricted to infiltrating leukocytes and was correlated quantitatively and by localization with interstitial CD3-positive T cells and CD68-positive macrophages. These first morphologic data on the distribution of CCR2-positive cells in human cGN suggest differential effects of chemokines and their receptors on the distribution of infiltrating leukocytes in different compartments of the kidney.

Renal epithelium is a previously unrecognized site of HIV-1 infection

The striking emergence of an epidemic of HIV-related renal disease in patients with end-stage renal disease provided the rationale for the exploration of whether HIV-1 directly infects renal parenchymal cells. Renal glomerular and tubular epithelial cells contain HIV-1 mRNA and DNA, indicating infection by HIV-1. In addition, circularized viral DNA, a marker of recent nuclear import of full-length, reverse-transcribed RNA, was detected in the biopsies, suggesting active replication in renal tissue. Infiltrating infected leukocytes harbored more viral mRNA than renal epithelium. Identification of this novel reservoir suggests that effectively targeting the kidney with antiretrovirals may be critical for patients who are seropositive with renal disease. Thus, renal epithelium constitutes a unique and previously unrecognized cell target for HIV-1 infection.

Macrophages infiltrating the tissue in chronic pancreatitis express the chemokine receptor CCR5

BACKGROUND

The immunologic mechanisms involved in the development of chronic pancreatitis (CP) are poorly understood. Chronically inflamed tissues contain increased numbers of mononuclear cells expressing the CC chemokine receptor 5 (CCR5), which is also a coreceptor for HIV entry of macrophagetropic strains. However, whether this receptor is involved in the inflammatory process in CP is not known. In the current study, we analyzed the expression of CCR5 in CP. The detection of chemokine receptors on inflammatory cells would strongly suggest their involvement in the pathogenesis of CP (i.e., attraction and activation of these cells). To further evaluate this, we consecutively analyzed the expression of 2 ligands of CCR5: RANTES and MIP-alpha.

METHODS

Pancreatic tissue samples of 22 patients with CP and of 7 healthy pancreas were evaluated. CCR5, RANTES, and MIP-1alpha were analyzed by Northern blot analysis. Consecutive tissue sections were stained for CCR5, CD3, and CD68 to define the leukocyte subtype expressing CCR5 in CP.

RESULTS

By Northern blot analysis, CCR5, RANTES, and MIP-1alpha messenger RNA (mRNA) levels were 12.9-fold, 13.3-fold and 9.2-fold higher in CP specimens compared with healthy controls, respectively (P<.01). Immunostaining for CCR5 revealed a 30-fold increase of CCR5-positive cells in CP tissue compared with the healthy pancreas. Staining of consecutive tissue sections revealed that the majority of CCR5-positive cells were also CD68-positive (macrophages).

CONCLUSIONS

Our data indicate that a remarkable portion of CCR5-positive cells in CP are macrophages. CCR5 is most likely involved in the attraction and activation of these macrophages, since the CCR5 ligands RANTES and MIP-1alpha are concomitantly upregulated.

Chemokines and their receptors in allograft rejection

Despite current recognition of over 40 chemokines and more than 18 chemokine receptors, understanding of their role in transplant immunobiology and transplant rejection is extremely limited and fragmentary. Recent literature has demonstrated the presence of chemokines and their receptors in transplants and some studies demonstrate important functional roles.

Infection of mesangial cells with HIV and SIV: identification of GPR1 as a coreceptor

BACKGROUND

Mesangial cells are an important component of the glomerulus. Dysfunction of mesangial cells is thought to be involved in the development of human immunodeficiency virus type 1 (HIV-1)-associated nephropathy (HIVAN). HIVAN is a structural renal failure frequently observed in patients with acquired immune deficiency syndrome. However, the susceptibility of mesangial cells to HIV-1 is disputable. More than ten G protein-coupled receptors, including chemokine receptors, have been shown to act as HIV-1 coreceptors that determine the susceptibilities of cells to HIV-1 strains with specific cell tropisms.

METHODS

We examined the susceptibility of mesangial cells to various HIV-1, HIV type 2 (HIV-2) and simian immunodeficiency virus (SIV) strains. Expression of CD4 and HIV/SIV coreceptors was examined by Western blotting and polymerase chain reaction.

RESULTS

Mesangial cells were found to be susceptible to HIV-1 variant and mutants that infect brain-derived cells, but highly resistant to T-tropic (X4), M-tropic (R5) or dual-tropic (X4R5) HIV-1 strains. In addition, mesangial cells were also susceptible to HIV-2 and SIV strains that infect the brain-derived cells. Among HIV/SIV coreceptors we tested, the expression of GPR1 mRNA was detected in mesangial cells. Expression of CD4 mRNA and protein was also detected in them. Mesangial cells and GPR1-transduced CD4-positive cells showed similar susceptibilities to the HIV-1 variant and mutants and HIV-2 and SIV strains.

CONCLUSIONS

CD4 and GPR1 mRNAs were detected in mesangial cells. Mesangial cells were susceptible to HIV/SIV strains that use GPR1 as a coreceptor. Our findings suggest that an orphan G protein-coupled receptor, GPR1, is a coreceptor expressed in mesangial cells. It remains to be investigated whether the interaction of mesangial cells with specific HIV-1 strains through GPR1 plays a role in the development of HIVAN.

Expression of chemokines and their receptors in nephrotoxic serum nephritis

BACKGROUND

Chemokines play a major role in leukocyte infiltration in inflammatory kidney diseases. The specificity of the chemokine action is determined by the restricted expression of the corresponding receptors on leukocytes. We therefore simultaneously studied the expression of CC-chemokine and CC-chemokine receptor 1-5 (CCR 1-5) mRNA in an accelerated model of nephrotoxic nephritis in CD-1 mice.

METHODS

Kidneys were harvested at day 0, 2 and 7. Induction of nephritis was confirmed by assessment of albuminuria by ELISA and by histological evaluation. RNA was prepared from cortex and isolated glomeruli. RNase protection assays were performed to study the expression of chemokines, RNase protection assays as well as quantitative RT-PCR assays to study the expression of chemokine receptors.

RESULTS

In the cortex of nephritic kidneys mRNA for MCP-1 was increased 5-fold on day 2 and increased 4-fold on day 7 as compared to controls. mRNA for RANTES was increased 5-fold on day 7 and mRNA for IP-10 6-fold on day 7. The increase of mRNA for the chemokine receptors CCR1 and 5 was between 2-fold and 3-fold determined by RNase protection assay and for CCR1, 2 and 5 between 2- and 4-fold as determined by RT-PCR. In isolated glomeruli we found by RT-PCR an increase of CCR1, CCR2 and CCR5 of between 3 and 12-fold.

CONCLUSION

These results show that chemokines and their specific chemokine receptors are increased in parallel in this model of glomerulonephritis, consistent with the potential role of the chemokine system in leukocyte recruitment to the immune injured kidney.

Distinct expression of CCR1 and CCR5 in glomerular and interstitial lesions of human glomerular diseases

We investigated the presence of CCR1- and CCR5-positive cells immunohistochemically in the kidneys of 38 patients with several renal diseases, including 13 crescentic glomerulonephritis patients. In addition, we determined cell phenotypes of CCR1- and CCR5-positive cells using a dual immunostaining technique. Urinary levels of their ligands, for CCR1 and CCR5; macrophage inflammatory protein (MIP)-1alpha, MIP-1beta and regulated upon activation in normal T cells expressed and secreted (RANTES) were evaluated by enzyme-linked immunosorbent assay. CCR1- and CCR5-positive cells were detected in both glomeruli and interstitium of the diseased kidneys. Using a dual immunostaining technique, these positive cells were CD68-positive macrophages (MPhi) and CD3-positive T cells. The number of CCR1-positive cells in glomeruli was correlated with urinary levels of MIP-1alpha. The number of CCR1-positive cells in the interstitium was correlated with both urinary MIP-1alpha and RANTES levels. CCR1-positive cells in the interstitium remained after glucocorticoid therapy, most of which were MPhi, and were correlated with the intensity of interstitial fibrosis and tubular atrophy. Glomerular CCR5-positive cells were well correlated with extracapillary lesions and urinary MIP-1alpha levels, while interstitial CCR5-positive cells, mainly CD3-positive T cells, were correlated with interstitial lesions and urinary RANTES levels. Renal CCR5-positive cells were dramatically decreased during convalescence induced by glucocorticoids. These results suggest that chemokine receptor signaling may be pivotal for human renal diseases through the recruitment and activation of MPhi and T cells; CCR5-positive cells may participate in glomerular lesions including extracapillary lesions via MIP-1alpha and in interstitial lesions via RANTES. CCR1 may be involved in interstitial lesions in resolving phase after glucocorticoid therapy.

Chemokine receptor CCR5 and CXCR4 expression in HIV-associated kidney disease

The chemokine receptors CCR5 and CXCR4 have been identified as essential coreceptors for entry of HIV-1 strains into susceptible cells. Direct infection of renal parenchymal cells has been implicated in the pathogenesis of HIV-associated renal disease, although data are conflicting. The localization of CCR5 and CXCR4 in kidneys with HIV-associated renal disease is unknown. Formalin-fixed, paraffin-embedded renal biopsies from patients with HIV-associated nephropathy (HIVAN) (n = 13), HIV-associated immune complex glomerulonephritis (n = 3), HIV-associated thrombotic microangiopathy (n = 1), and HIV-negative patients with collapsing glomerulopathy (n = 8) were analyzed in this study. Cellular sites of expression of CCR5 and CXCR4 were identified by immunohistochemistry and by in situ hybridization. The presence of HIV-1 was detected by immunohistochemistry and by in situ hybridization. Expression of both chemokine receptors CCR5 and CXCR4 was undetectable in intrinsic glomerular, tubular, and renovascular cells in all analyzed cases. In the presence of tubulointerstitial inflammation, CCR5 and CXCR4 expression was localized to infiltrating mononuclear leukocytes. HIV-1 protein was undetectable by immunohistochemistry in all cases of HIV-associated renal disease. HIV-1 RNA was identified in one case of HIVAN but was restricted to infiltrating leukocytes. HIV-1 RNA was not detected in intrinsic renal cells in all analyzed cases. Identifying the cellular expression of HIV-coreceptors CCR5 and CXCR4 may help to clarify which tissues are permissive for direct HIV infection. These data do not support a role of productive HIV-1 infection of renal parenchymal cells in the pathogenesis of HIV-associated renal disease.

Chemokine blockade as a therapy for renal disease

Chemokines have been verified as inflammatory mediators of experimental nephritis by using anti-chemokine antibodies, chemokine receptor antagonists or targeted chemokine gene disruption. In human disease, chemokines are expressed in the kidney in association with inflammatory infiltrates. Chemokine blockade is thus a potentially novel approach to therapy of inflammatory renal disease. Several anti-chemokine strategies are under development. Effective use of anti-chemokine therapy for renal disease will require a precise understanding of the unique roles that individual chemokines have in renal pathology, and the genetic factors that regulate chemokine expression.

Rapid shift from virally infected cells to germinal center-retained virus after HIV-2 infection of macaques

Lymphoid tissues are the primary target during the initial virus dissemination that occurs in HIV-1-infected individuals. Recent advances in antiretroviral therapy and techniques to monitor virus load in humans have demonstrated that the early stages of viral infection and host response are major determinants of the outcome of individual infections. Relatively little is known about immunopathogenic events occurring during the acute phase of HIV infection. We analyzed viral dissemination within lymphoid tissues by in situ hybridization and by combined immunohistochemistry/in situ hybridization during the acute infection phase (12 hours to 28 days) in pig-tailed macaques (Macaca nemestrina), challenged intravenously with a virulent strain of HIV-2, HIV-2(287). Two stages in viral dissemination were clearly evident within the first 28 days after HIV-2(287) infection. First, a massive increase in individual HIV-2-infected cells, mostly CD3+ T lymphocytes and a smaller percentage of macrophages and interdigitating dendritic cells, was identified within lymph nodes which peaked on the 10th day after HIV-2 infection. A shift of HIV-2 distribution was demonstrable between day 10 and day 14 after HIV-2 infection. Coincident with a marked reduction in individual HIV-2 RNA+ cells by day 14 postinfection, there was a dramatic increase in germinal center-associated HIV-2 RNA. High concentrations of HIV-2 RNA persisted in germinal centers in all animals by days 21 and 28 postinfection. Thus, HIV-2 appears to go through an initial, highly disseminated cellular phase followed by localization in the follicular dendritic cell network with relatively few infected cells. In this nonhuman primate model of HIV-associated immunopathogenesis, using a virus derived from a human pathogen, we identified a significant shift in the pattern of HIV-2 localization within a narrow time frame (day 10 to day 14). This shift in virus localization and behavior indicates that there may be a discrete but remarkably narrow window for therapeutic interventions that interrupt this stage in the natural course of HIV infection. Reproducibility and the accelerated time course of disease development make this model an excellent candidate for such intervention studies.

The nephropathies of HIV infection: pathogenesis and treatment

Several different renal syndromes have been reported in patients with HIV infection. Patient characteristics and a syndrome approach may help the clinician formulate a tentative diagnosis, but a renal biopsy is necessary to make a firm diagnosis in patients with chronic renal disease in the setting of HIV infection. The pathogenesis of the HIV nephropathies can teach us much about the pathophysiology of common renal problems such as IgA nephropathy, immune complex glomerulonephritis, focal segmental glomerulosclerosis, and diabetic renal disease. HIV-associated renal disease may be the result of the interaction of the expression of specific HIV genes in patients with distinct genetic susceptibilities to disease in particular environments. New treatment approaches have provided hope for patients with classic HIV-associated nephropathy.

Renal allograft rejection: beta-chemokine involvement in the development of tubulitis

BACKGROUND

Tubulitis is a defining feature of renal allograft rejection. Graft dysfunction may result from damage inflicted on tubular epithelial cells by intratubular cytotoxic T lymphocytes. Graft cells are known to produce chemokines during acute rejection, but it is not known whether changes in expression of specific chemokines can influence the composition of the intratubular lymphocyte population. We examined expression of individual chemokines in biopsy sections showing different pathological rejection grades.

METHODS

Sections from Banff-graded transplant biopsies were examined for the presence of beta-chemokines (MCP-1, MIP-1alpha, MIP-1beta, and RANTES) by immunofluorescence and semiquantitative confocal laser scanning microscopy.

RESULTS

Beta-chemokines were expressed predominantly at the basolateral surface of tubular epithelial cells. Expression of MCP-1 and MIP-1beta was significantly higher in sections showing grade 2 rather than grade 1 acute rejection. RANTES and MIP-1alpha showed no significant variation in level of expression between rejection grades.

CONCLUSIONS

Beta-chemokines are expressed by tubular epithelial cells during acute rejection. Consistent expression of RANTES and MIP-1alpha suggests a general role in recruiting T lymphocytes. However, MCP-1 and MIP-1beta may play a more subtle role in recruitment of specific T-cell subsets, such as Th1 cells, during acute cellular rejection.

Targeting of the chemokine receptor CCR1 suppresses development of acute and chronic cardiac allograft rejection

Although mononuclear cell infiltration is a hallmark of cellular rejection of a vascularized allograft, efforts to inhibit rejection by blocking leukocyte-endothelial cell adhesion have proved largely unsuccessful, perhaps in part because of persistent generation of chemokines within rejecting grafts. We now provide, to our knowledge, the first evidence that in vivo blockade of specific chemokine receptors is of therapeutic significance in organ transplantation. Inbred mice with a targeted deletion of the chemokine receptor CCR1 showed significant prolongation of allograft survival in 4 models. First, cardiac allografts across a class II mismatch were rejected by CCR1(+/+) recipients but were accepted permanently by CCR1(-/-) recipients. Second, CCR1(-/-) mice rejected completely class I- and class II-mismatched BALB/c cardiac allografts more slowly than control mice. Third, levels of cyclosporin A that had marginal effects in CCR1(+/+) mice resulted in permanent allograft acceptance in CCR1(-/-) recipients. These latter allografts showed no sign of chronic rejection 50-200 days after transplantation, and transfer of CD4(+) splenic T cells from these mice to naive allograft recipients significantly prolonged allograft survival, whereas cells from CCR1(+/+) mice conferred no such benefit. Finally, both CCR1(+/+) and CCR1(-/-) allograft recipients, when treated with a mAb to CD4, showed permanent engraftment, but these allografts showed florid chronic rejection in the former strain and were normal in CCR1(-/-) mice. We conclude that therapies to block CCR1/ligand interactions may prove useful in preventing acute and chronic rejection clinically.

Chemokines, chemokine receptors, and renal disease: from basic science to pathophysiologic and therapeutic studies

Leukocyte trafficking from peripheral blood into affected tissues is an essential component of the inflammatory reaction to virtually all forms of injury and is an important factor in the development of many kidney diseases. Advances in the past few years have highlighted the central role of a family of chemotactic cytokines called chemokines in this process. Chemokines help to control the selective migration and activation of inflammatory cells into injured renal tissue. Chemokines and their receptors are expressed by intrinsic renal cells as well as by infiltrating cells during renal inflammation. This study summarizes the in vitro and in vivo data on chemokines and chemokine receptors in renal diseases with a special focus on potential therapeutic effects on inflammatory processes.

Thrombotic microangiopathy in the HIV-2-infected macaque

Thrombotic microangiopathy (TMA) has been increasingly reported in human immunodeficiency virus (HIV)-infected humans over the past decade. The pathogenesis is unknown. We prospectively analyzed the renal pathology and function of 27 pigtailed macaques (Macaca nemestrina), infected intravenously with a virulent HIV-2 strain, HIV-2(287), in addition to that of four uninfected control macaques. Necropsies were performed between 12 hours and 28 days after infection. HIV-2 antigen was detectable in peripheral blood mononuclear cell (PBMC) cocultures in all animals after 10 days of HIV-2 infection; a rapid decline in CD4(+) PBMC (<350/microliter) was seen in five of six animals 21 days and 28 days after infection. No macaque developed features of clinical AIDS. Typical lesions of human HIV-associated nephropathy were undetectable. Six of the 27 HIV-2-infected macaques demonstrated both histological TMA lesions (thrombi in glomerular capillary loops and small arteries, mesangiolysis) and ultrastructural lesions (mesangiolysis, subendothelial lucency, platelet thrombi in glomerular capillary lumina). Extrarenal thrombi were detected in the gastrointestinal and adrenal microvasculature of macaques that had developed renal TMA. None of the control animals demonstrated features of renal TMA at necropsy. In a retrospective analysis of kidneys obtained from 39 additional macaques infected with HIV-2(287), seven cases demonstrated TMA. In situ hybridization showed no detectable HIV-2 RNA in kidney sections of 65/66 HIV-2-infected macaques, including all 13 TMA cases. Expression of the chemokine receptor CXCR4, the putative coreceptor for HIV-2(287), was absent in intrinsic renal cells in all HIV-2-infected macaques. The HIV-2-infected macaque may be a useful model of human HIV-associated TMA. Our data do not support a role of direct HIV-2 infection of intrinsic renal cells as an underlying mechanism.

Expression of the C-C chemokine receptor 5 in human kidney diseases

BACKGROUND

Chemokines are proteins that contribute to the migration of leukocytes to sites of tissue injury. CCR5 is a receptor for the C-C chemokine RANTES, which is expressed in inflammatory kidney diseases and transplant rejection.

METHODS

In order to study the distribution of CCR5, we developed a series of monoclonal antibodies against human CCR5. These antibodies were then evaluated by flow cytometry, Western blot, and immunohistochemistry on formalin-fixed, paraffin-embedded tonsils. Eighty biopsies from patients with membranous glomerulonephritis (N = 9), IgA nephropathy (N = 10), lupus nephritis (N = 10), membranoproliferative glomerulonephritis (N = 10), acute interstitial nephritis (N = 13), chronic interstitial nephritis (N = 10), acute transplant rejection (N = 9), and chronic transplant rejection (N = 9) were stained for CCR5 and CD3 expression in parallel sections.

RESULTS

One monoclonal antibody (MC-5) showed a single protein band of approximately 38 kD corresponding to CCR5 in Western blot. By indirect immunohistochemistry, a cell membrane signal was detected exclusively on mononuclear inflammatory cells. All control stainings with an isotype-matched mouse IgG2a were negative. CCR5-positive cells were identified in areas of interstitial infiltration in biopsies of chronic glomerulonephritis, interstitial nephritis, and transplant rejection. The staining of CCR5 showed the same distribution as CD3-positive T cells. In patients with impaired renal function, a significantly higher number of CCR5-positive cells were found as compared with patients with normal renal function. In contrast to the prominence of CCR5-positive cells in the interstitial infiltrate, the number of CCR5-positive cells within the glomeruli was low, even in cases with proliferative glomerulonephritis. No CCR5 expression could be detected on intrinsic cells of glomerular, tubular, or vascular structures.

CONCLUSIONS

The pattern of CCR5 and CD3 cell infiltration suggests that CCR5-positive T cells may play a role in interstitial processes leading to fibrosis. Further studies are required to define the pathophysiological relevance of these cells in progressive renal diseases.