The effect of complement regulatory protein expression on pig endothelial cells to porcine endogenous retrovirus lyses by human sera

INTRODUCTION

Expression of human complement regulatory proteins (CRP) on pig endothelial cells (PEC) has been useful to avoid hyperacute rejection by human sera. On the other hand, porcine endogenous retrovirus (PERV) from PEC transfectants with CRP may acquire resistance to human sera. In this study, we investigated the effects of the transfected CRP on PERV neutralization and/or lysis by human sera.

METHODS

cDNA of membrane cofactor protein (MCP: CD46), decay accelerating factor (DAF: CD55), and CD59 were transfected to PEC lines by lipofection. The expressions of these CRPs were verified by FACS analysis. The PEC lines with human CRPs were then transfected with the LacZ gene and PERV subtype B (PERV-B) to investigate PERV infectivity by LacZ pseudotype assay. Culture supernates of PEC were inoculated to HEK293 cells with or without 10% human sera. The inoculated 293 cells were then histochemically stained to count the LacZ-positive blue foci and calculated the rate of reduction of LacZ-positive cells by serum.

RESULTS

PERV from the PEC with DAF or CD59 showed a resistance to human sera compared with those of control PEC (DAF: 59.6% +/- 5.3%, CD59: 61.1% +/- 3.9% vs control: 31.3% +/- 3.6%; P < .01). However, PEC with MCP did not cause such an effect (28.8% +/- 2.5%).

CONCLUSIONS

While expression of DAF and CD59 on PEC changed its PERV responsiveness to human sera, MCP did not improve it.

Experimental transmission of abnormal prion protein (PrPsc) in the small intestinal epithelial cells of neonatal mice

Using an immunohistochemical method, we attempted to detect the transmission of abnormal prion protein (PrPsc) to the enterocytes of the small intestine of neonatal mice by oral exposure with sheep brain affected by scrapie. Five 1-day-old neonatal mice were exposed by oral inoculation to the homogenized brain of a scrapie-affected sheep. In the small intestine of all mice 1 hour after inoculation, immunoreactivity with antinormal prion protein (PrPc) antibody was seen in the cytoplasm of villus enterocytes. This finding suggests transmission of abnormal PrPsc into the cytoplasm of enterocytes. In control mice treated with normal sheep brain, no PrPc signal was seen in enterocytes of the small intestine. Immunopositivity for neurofilament protein and glial fibrillary acidic protein was seen in the cytoplasm of enterocytes of mice inoculated with scrapie and normal sheep brain. This suggests that the enterocytes of neonatal mice can absorb PrPsc and other macromolecular proteins of the sheep brain affected by scrapie and may be more important than previously thought as a pathway for PrPsc transmission in neonatal animals.

Experimental vertical transmission of Borna disease virus in the mouse

We demonstrated the experimental vertical transmission of Borna disease virus (BDV) in pregnant BALB/c mice. Giessen strain He/80 of BDV was used in the present study. Six six-week-old mice were inoculated intraperitoneally with 10(5) 50% tissue culture infective doses (TCID50), and were bred immediately. Four pregnant mice were sacrificed under anaesthesia on the 10th and 14th days after vaginal plug formation. Nine newborns from two maternal mice were sacrificed under anaesthesia on the 7th day after birth. Positive signals with RT-nested PCR techniques for BDV p24-RNAs were seen in the fetuses, placentas and brains of all newborn mice. No immunopositivities for BDV p40 were found in the fetuses or placentas at 10 days' gestation. BDV p40 immunopositivities were found in neurons of the fetal brains and in decidual cells of the placentas at 14 days' gestation. They were also found in neurons of the brains of newborn mice. At 10 days' gestation, no positive signals for BDV p40 sense or antisense riboprobes were seen in the fetal brains or placentas. Positive signals were found in neurons of the fetal brains and decidual cells of the placentas at 14 days' gestation. Positive signals for BDV p40 sense and antisense riboprobes were found in almost all neurons throughout the brains of nine newborn mice. These results suggest that persistent infection with BDV in newborn mice may be induced by vertical transmission during gestation.

Borna disease virus phosphoprotein binds a neurite outgrowth factor, amphoterin/HMG-1

The Borna disease virus (BDV) p24 phosphoprotein is an abundant protein in BDV-infected cultured cells and animal brains. Therefore, there is a possibility that binding of the p24 protein to cellular factor(s) induces functional alterations of infected neural cells in the brain. To identify a cellular protein(s) that interacts with BDV p24 protein, we performed far-Western blotting with extracts from various cell lines. Using recombinant p24 protein as a probe, we detected a 30-kDa protein in all cell lines examined. Binding between the 30-kDa and BDV p24 proteins was also demonstrated using BDV p24 affinity and ion-exchange chromatography columns. Microsequence analysis of the purified 30-kDa protein revealed that its N terminus showed complete homology with rat amphoterin protein, which is a neurite outgrowth factor abundant in the brain during development. Mammalian two-hybrid and immunoprecipitation analyses also confirmed that amphoterin is a specific target for the p24 protein in vivo. Furthermore, we showed that infection by BDV, as well as purified p24 protein in the medium, significantly decreased cell process outgrowth of cells grown on laminin, indicating the functional inhibition of amphoterin by interaction with the p24 protein. Immunohistochemical analysis revealed decreased levels of amphoterin protein at the leading edges of BDV-infected cells. Moreover, the expression of the receptor for advanced glycation end products, of which the extracellular moiety is a receptor for amphoterin, was not significantly activated in BDV-infected cells during the process of extension, suggesting that the secretion of amphoterin from the cell surface is inhibited by the binding of the p24 protein. These results suggested that BDV infection may cause direct damage in the developing brain by inhibiting the function of amphoterin due to binding by the p24 phosphoprotein.

[The neuropathogenesis of Borna disease virus infection]

Borna disease virus(BDV) is a noncytolytic, neurotropic RNA virus that causes a disease of the central nervous system(CNS) in several vertebrate species, including horses, sheep, cats and ostriches. Epidemiological studies using peripheral blood or brain samples revealed that BDV can infect humans and that it may be related with certain neuropsychiatric disorders. The unique genetic and biological properties of BDV indicate that BDV develops a persistent infection in the CNS. Furthermore, a line of recent evidences suggests that BDV infection causes direct effects on brain functions in the absence of immunopathology-related brain damage. In this review, we discuss about recent data regarding neuropathogenesis of BDV infections in animals and humans.

Borna disease virus nucleoprotein requires both nuclear localization and export activities for viral nucleocytoplasmic shuttling

Nuclear transport of viral nucleic acids is crucial to the life cycle of many viruses. Borna disease virus (BDV) belongs to the order Mononegavirales and replicates its RNA genome in the nucleus. Previous studies have suggested that BDV nucleoprotein (N) and phosphoprotein (P) have important functions in the nuclear import of the viral ribonucleoprotein (RNP) complexes via their nuclear targeting activity. Here, we showed that BDV N has cytoplasmic localization activity, which is mediated by a nuclear export signal (NES) within the sequence. Our analysis using deletion and substitution mutants of N revealed that NES of BDV N consists of a canonical leucine-rich motif and that the nuclear export activity of the protein is mediated through the chromosome region maintenance protein-dependent pathway. Interspecies heterokaryon assay indicated that BDV N shuttles between the nucleus and cytoplasm as a nucleocytoplasmic shuttling protein. Furthermore, interestingly, the NES region overlaps a binding site to the BDV P protein, and nuclear export of a 38-kDa form of BDV N is prevented by coexpression of P. These results suggested that BDV N has two contrary activities, nuclear localization and export activity, and plays a critical role in the nucleocytoplasmic transport of BDV RNP by interaction with other viral proteins.

Neurological diseases and viral dynamics in the brains of neonatally borna disease virus-infected gerbils

Borna disease virus (BDV) is a noncytolytic, neurotropic RNA virus that causes a chronic neurological disease in a wide variety of animal species. To develop a better understanding of the correlation between neurological disorders caused by BDV infection and virus distribution in the brain, we investigated viral dynamics in the central nervous system (CNS) of neonatally BDV-infected gerbils during the late stage of infection. Despite the severe symptoms and aggressive proliferation of BDV in the infected gerbils, no apparent neuroanatomical abnormalities or neuronal cell loss was observed in the infected gerbil brain. Furthermore, no or only minimal infiltration was observed in the infected gerbil brain. By in situ hybridization and real-time PCR analyses, we demonstrated that the predominant area of expression of BDV mRNA, as well as the protein, was shifted in the brain in association with progression of disease. In nondiseased gerbils, the virus replication was predominantly detected in the cerebral cortex and hippocampus of the CNS. On the other hand, diseased animals showed a high level of expression in the lower brain stem and cerebellum, especially in Purkinje cell neurons. These observations suggested that significant replication of the virus in specific areas of the CNS is critical for development of the neurological disorders in BDV-infected neonatal gerbils.

Molecular ratio between borna disease viral-p40 and -p24 proteins in infected cells determined by quantitative antigen capture ELISA

We developed the antigen capture enzyme-linked immunosorbent assay (ELISA) systems for quantification of Borna disease virus (BDV) major antigens, p40 and p24. Using these ELISAs, we quantified the two proteins in various BDV-infected materials, including the cell lysates and culture supernatants as well as the homogenates of experimental animal brains. The ELISAs were also applied to measure the infectious titer of BDV in persistently infected cell lines. Quantitative analysis with these ELISAs allowed us to measure the molecular ratio between the p40 and p24 in infected samples. Interestingly, the ratio of p24 to p40 in persistently infected cells was much higher than that observed in acutely infected cells although the ratios in the supernatants from both cell lines were quite similar. BDV-inoculated gerbil brain cells showed a relatively high ratio of p24 to p40 as compared with acutely infected cells. These observations suggested that the molecular ratio between the proteins strongly depended on the infectious status of BDV in the host cells. The ELISA system developed here could be a convenient method for the quantification of BDV infection and may also be beneficial for understanding viral replication and infectious status in the host cells.

Translation initiation of a bicistronic mRNA of Borna disease virus: a 16-kDa phosphoprotein is initiated at an internal start codon

We examined translational initiation of a bicistronic 0.8-kb mRNA of Borna disease virus (BDV) using a cDNA clone of the mRNA. Upon transfection with the clone, COS-7 cells produced a 16-kDa protein (P'), in addition to the previously identified products of BDV, 24- (P) and 14.5-kDa proteins. The 16-kDa product was detected by anti-P monoclonal antibody and was shown to exist in BDV-infected cell lines as well as in infected animal brain cells. Transient expression analysis of mutated cDNA clones encoding the BDV 0.8-kb mRNA revealed that the 16-kDa protein was initiated at the second AUG codon on the same open reading frame of the P protein. The mutational analysis also demonstrated that the first AUG within the 0.8-kb mRNA is not optimal, although the signal contains a better Kozak's motif. These results demonstrated the presence of three functional AUG codons in the smallest mRNA of BDV and also suggested that a leaky scanning mechanism is involved in translational initiation at AUG codons downstream of the bicistronic mRNA of BDV. Furthermore, the 16-kDa protein was located in the BDV-specific nuclear foci and was found to associate with the other viral proteins in BDV-infected cells, demonstrating an important role of the novel identified BDV protein in viral replication.

Identification of alternative splicing and negative splicing activity of a nonsegmented negative-strand RNA virus, Borna disease virus

Borna disease virus (BDV) is a nonsegmented negative-strand RNA virus that belongs to the Mononegavirales. Unlike other animal viruses of this order, BDV replicates and transcribes in the nucleus of infected cells. Previous studies have shown that BDV uses RNA splicing machinery for its mRNA expression. In the present study, we identified spliced RNAs that use an alternative 3' splice site, SA3, in BDV-infected cell lines as well as infected animal brain cells. Transient transfection analysis of cDNA clones of BDV RNA revealed that although SA3 is a favorable splice site in mammalian cells, utilization of SA3 is negatively regulated in infected cells. This negative splicing activity of the SA3 site is regulated by a putative cis-acting region, the exon splicing suppressor (ESS), within the polymerase exon of BDV. The BDV ESS contains similar motifs to other known ESSs present in viral and cellular genes. Furthermore, our results indicated that a functional polyadenylation signal just upstream of the BDV ESS is also involved in the regulation of alternative splicing of BDV. These observations represent the first documentation of complex RNA splicing in animal RNA viruses and also provide new insight into the mechanism of regulation of alternative splicing in animal viruses.

Antibodies to Borna disease virus in infected adult rats: an early appearance of anti-p10 antibody and recognition of novel virus-specific proteins in infected animal brain cells

The time course for appearance of antibodies to Borna disease virus (BDV) major antigens, p40, p24, p18 and p10 were investigated in BDV-inoculated adult rats by Western blotting. Anti-p10 antibodies were detected in sera as early as anti-p40 and -p24 antibodies at four or five weeks after inoculation. Furthermore, in addition to these major antigens of BDV, the rat serum could detect additional 80-, 58-, 43-, 20-, and 16-kDa proteins in BDV-infected cultured cells and/or animal brain cells by Western blot analysis. Of these proteins, the 20- and 16-kDa proteins were shown to be related to p24 protein by their reactivity with anti-p24 monoclonal antibody. Interestingly, the 58- and 24-kDa were found only in BDV-infected animal brain cells but not in cultured cells. The results in this study could provide a useful information on the mechanism for the viral replication and pathogenesis.

Isolation of Borna disease virus from human brain tissue

Serological and molecular epidemiological studies indicate that Borna disease virus (BDV) can infect humans and is possibly associated with certain neuropsychiatric disorders. We examined brain tissue collected at autopsy from four schizophrenic patients and two healthy controls for the presence of BDV markers in 12 different brain regions. BDV RNA and antigen was detected in four brain regions of a BDV-seropositive schizophrenic patient (P2) with a very recent (2 years) onset of disease. BDV markers exhibited a regionally localized distribution. BDV RNA was found in newborn Mongolian gerbils intracranially inoculated with homogenates from BDV-positive brain regions of P2. Human oligodendroglia (OL) cells inoculated with brain homogenates from BDV-positive gerbils allowed propagation and isolation of BDVHuP2br, a human brain-derived BDV. Virus isolation was also possible by transfection of Vero cells with ribonucleoprotein complexes prepared from BDV-positive human and gerbil brain tissues. BDVHuP2br was genetically closely related to but distinct from previously reported human- and animal-derived BDV sequences.

[Henoch-Schönlein purpura nephritis (HSPN) in children: comparison of the incidence and severity between two 12-year groups]

From 1971 to 1982, we treated 286 patients of HSP in Kitasato University Hospital. In these 286 patients, 137 developed purpura nephritis (47.9%). During the second 12-year period (from 1985 to 1996), we treated 34 HSPN patients among 189 HSP patients (18.0%). The clinico-pathological evaluations and comparisons in 30 cases from 1971 to 1982 and in 11 cases from 1985 to 1996 were performed, using the ISKDC grading. The numbers of patients of HSP and the incidence of HSPN both decreased in the more recent 12-year group. Furthermore, the severity of the renal histopathological findings decreased in the more recent group as well.

Structures of endogenous nonecotropic murine leukemia virus (MLV) long terminal repeats in wild mice: implication for evolution of MLVs

To develop a better understanding of the interaction between retroviruses and their hosts, we have investigated the polymorphism in endogenous murine leukemia proviruses (MLVs). We used genomic libraries of wild mouse DNAs and PCR to analyze genetic variation in the proviruses found in wild mouse species, including Mus musculus (M. m. castaneus, M. m. musculus, M. m. molossinus, and M. m. domesticus), Mus spretus, and Mus spicelegus, as well as some inbred laboratory strains. In this analysis, we detected several unique forms of sequence organization in the U3 regions of the long terminal repeats of these proviruses. The distribution of the proviruses with unique U3 structures demonstrated that xenotropic MLV-related proviruses were present only in M. musculus subspecies, while polytropic MLV-related proviruses were found in both M. musculus and M. spretus. Furthermore, one unique provirus from M. spicelegus was found to be equidistant from ecotropic provirus and nonecotropic provirus by phylogenetic analysis. This provirus, termed HEMV, was thus likely to be related to the common ancestor of these MLVs. Moreover, an ancestral type of polytropic MLV-related provirus was detected in M. spretus species. Despite their "ancestral" phylogenetic position, proviruses of these types are not widespread in mice, implying more-recent spread by infection rather than inheritance. These results imply that recent evolution of these proviruses involved alternating periods of replication as virus and residence in the germ line.

Epitopes and nuclear localization analyses of canine distemper virus nucleocapsid protein by expression of its deletion mutants

A series of nucleocapsid protein (NP)-deleted genes of the Onderstepoort strain was constructed in order to locate antigenic regions of the NP of canine distemper virus. The expression of proteins from 5'-deleted NP genes was examined in COS-7 cells by indirect immunofluorescence assay using three monoclonal antibodies (MAbs), c-5, f-5 and h-6, and a rabbit serum against NP. These MAbs reacted with two regions of NP. Amino acid residues from 1 to 80, and 337-358, were necessary and sufficient for formation of the epitopes identified by MAbs f-5 and h-6, and c-5, respectively. The proteins translated from intact or 3'-deleted genes were found to be localized in the nuclei of COS-7 cells, whereas the proteins from the 5'-deleted genes were mainly detected in the cytoplasm. These results suggested that 80 amino acid residues at the N-terminus are required for transportation of NP into the nucleus.

Structure and distribution of endogenous nonecotropic murine leukemia viruses in wild mice

Virtually all of our present understanding of endogenous murine leukemia viruses (MLVs) is based on studies with inbred mice. To develop a better understanding of the interaction between endogenous retroviruses and their hosts, we have carried out a systematic investigation of endogenous nonecotropic MLVs in wild mice. Species studied included four major subspecies of Mus musculus (M. m. castaneus, M. m. musculus, M. m. molossinus, and M. m. domesticus) as well as four common inbred laboratory strains (AKR/J, HRS/J, C3H/HeJ, and C57BL/6J). We determined the detailed distribution of nonecotropic proviruses in the mice by using both env- and long terminal repeat (LTR)-derived oligonucleotide probes specific for the three different groups of endogenous MLVs. The analysis indicated that proviruses that react with all of the specific probes are present in most wild mouse DNAs tested, in numbers varying from 1 or 2 to more than 50. Although in common inbred laboratory strains the linkage of group-specific sequences in env and the LTR of the proviruses is strict, proviruses which combine env and the LTR sequences from different groups were commonly observed in the wild-mouse subspecies. The "recombinant" nonecotropic proviruses in the mouse genomes were amplified by PCR, and their genetic and recombinant natures were determined. These proviruses showed extended genetic variation and provide a valuable probe for study of the evolutionary relationship between MLVs and the murine hosts.

Characterization of an integrase mutant of feline immunodeficiency virus

The role of the integrase region of feline immunodeficiency virus (FIV) in viral replication was examined using an integrase mutant clone of FIV which carries a frameshift mutation in the region. Upon transfection, although the integrase mutant was able to release virus-like particles into the supernatant from the transfected cells, the virions produced by the mutant contained unprocessed gag precursor protein and undetectable levels of reverse transcriptase activity. Furthermore, the mutant virions were unable to direct the synthesis of viral DNA after infection in target cells. To understand this phenotype of the integrase mutant in more detail, we constructed a gag-pol expression plasmid from an FIV molecular clone and assayed roles of the integrase region on virus particle formation following transfection. When an inframe deletion was introduced into the protease region of the expression plasmid, the mutant was able to efficiently release gag- and gag-pol precursor proteins into the supernatant from the transfected cells. An expression plasmid with mutations in both the protease and integrase regions, however, failed to release the gag-pol precursor protein from the cells. These results suggested an essential role for the integrase region for efficient incorporation of the gag-pol precursor into the virions.

Replication of feline syncytial virus in feline T-lymphoblastoid cells and induction of apoptosis in the cells

Feline syncytial virus (FSV) was isolated from feline peripheral blood mononuclear cells of FSV-seropositive cats. When the susceptibility of feline T-lymphocytes to FSV was examined using three strains of FSV, FSV antigens were detected in the FSV-infected T-lymphoblastoid cells. Further, a diversity of biological properties, including replication kinetics and syncytia formation, was noted among the strains, and condensation of chromatin and the fragmentation of cellular DNA were observed in the infected cells. From these data, we conclude that FSV is lymphotropic and can induce apoptosis in the lymphocytes.

Expression of the nucleocapsid protein gene of the canine distemper virus

We constructed a cDNA clone of canine distemper virus (CDV) encoding an entire nucleoprotein (NP) gene, by means of the reverse transcription-polymerase chain reaction (RT-PCR). The cloned NP gene was inserted into the eucaryotic expression vector, pRVSV. After transfection of the plasmid into Vero cells, we examined the expression of CDV-specific NP antigen by means of indirect immunofluorescence assay (IFA) and Western blotting, using various antibodies against NP of CDV and an antiserum against NP of measles virus. The CDV-NP specific antigen was detected in the nuclei of the cells transfected with pRV-ON, by means of IFA with antibodies specific to the NP.

[Membranous nephropathy in Japanese children]

Since 1973, 15 patients, consisting of 8 boys and 7 girls, were diagnosed as having membranous nephropathy (MN). The average age at detection was 8.2 years (2-14 years). The presenting symptom was edema in 1, pyrexia in 1 and upper respiratory infection in 1 case, in the all other cases, abnormal urinalysis was detected by the school or chance urinalysis. Surface antigen of hepatitis B virus (HBs) was positive in 6 patients and negative in 9. Anti-nuclear antibody (ANA) was positive in 3 and negative in 11. In one patient, ANA was not tested. One patient who was negative for ANA was diagnosed as having SLE 4 years later. At the last follow-up, 10 patients continued to have urinary abnormalities. Among these was one case positive for HBs antigen who went into end-stage renal failure. In the other 14 patients, the serum creatinine level was below 1.4 mg/dl. All patients showed a normal mesangium or mild mesangial proliferation. The patient diagnosed as having SLE. 4 years later showed mesangial deposits at the first renal biopsy. In our experience, most patients with MN were detected by the school or chance urinalysis and six of the these had positive HBs antigen. Lupus nephritis must be ruled out in making a diagnosis of idiopathic MN.

Roles of the auxiliary genes and AP-1 binding site in the long terminal repeat of feline immunodeficiency virus in the early stage of infection in cats

To examine the roles of auxiliary genes and the AP-1 binding site in the long terminal repeat of feline immunodeficiency virus (FIV) in vivo, three mutant viruses, which are defective in the vif gene ([delta]vif), ORF-A gene (deltaORF-A), and AP-1 binding site (deltaAP-1), and wild-type virus as a positive control were separately inoculated into three specific-pathogen-free cats. These cats were assessed by measuring the number of proviral DNA copies in peripheral blood mononuclear cells (PBMCs), the CD4/CD8 ratio and antibody responses to FIV for 16 weeks and then examining histological changes at necropsy. Although viral DNAs were detected in PBMCs from all 12 cats to various degrees until 16 weeks postinoculation, no virus was recovered from PBMCs of cats infected with (delta)vif virus during the observation period. However, a very weak antibody response was induced in one cat infected with the (delta)vif virus. In contrast, despite the successful recovery of virus from both groups of cats infected with deltaORF-A and deltaAP-1 virus, antibody responses and decrease in the CD4/CD8 ratio in the groups were milder than those in cats infected with wild-type virus. Furthermore, the numbers of proviral DNA copies in PBMCs from the two groups were not able to reach the level in cats infected with wild-type virus during the observation period. From these results, we conclude that these mutant viruses are still infectious for cats but failed in efficient viral replication and suggest that these auxiliary genes and enhancer element are important or essential to full viral replication kinetics and presumably to full pathogenicity during the early stage of infection in vivo.

Persistence of high virus neutralizing antibody titers in cats experimentally infected with feline immunodeficiency virus

The development of virus neutralizing (VN) antibody is one of the most effective host defense mechanisms against virus infection. In the present study, we developed a new VN assay against feline immunodeficiency virus (FIV) using a feline T-lymphoblastoid cell line, MYA-1 cells, based on inhibition of viral reverse transcriptase production. This assay is applicable to strains of FIV which can not infect CRFK cells. By using the assay, we examined long-term responses of VN antibody in cats experimentally infected with FIV. VN antibody titers increased progressively during first 30 weeks post inoculation and remained at high titers thereafter for 7 years of observation periods.

Genetic diversity of Argentine isolates of feline immunodeficiency virus

We report the nucleotide sequence and genetic diversity of part of the envelope (env) gene of four strains of feline immunodeficiency virus (FIV) isolated from Argentine domestic cats. The DNA encoding the V3 to V5 regions of the env gene of the FIV isolates were amplified by PCR, cloned and sequenced. Phylogenetic analysis revealed that the Argentine isolates did not cluster into a single group; one isolate clustered with subtype B FIV isolated in the USA and Japan, whereas the others formed a new cluster of FIV which might represent a prototype sequence for subtype E.

Feline immunodeficiency virus can infect a human cell line (MOLT-4) but establishes a state of latency in the cells

Infectivity of feline immunodeficiency virus (FIV) in feline and human lymphoblastoid cell lines was examined using homogeneous populations of FIV derived from infectious molecular clones of strains TMZ and Petaluma, and two recombinant chimeric clones carrying gag, pol, vif and ORF-A from the heterologous virus. FIV from the clones with the env region of the Petaluma strain was shown to infect and establish provirus in a human lymphoid cell line (MOLT-4), although the FIV-infected cells did not produce any infectious viruses. By treatment of the infected MOLT-4 cells with a phorbol ester, infectious virus was rescued. To examine which stage of the life-cycle of FIV is blocked in these cells, we analysed transcription of FIV-14 in the cells by RT-PCR. FIV-specific RNA expression could not be detected. These results strongly suggest that latency of the virus in MOLT-4 cells is due to a failure in transcription.

[Extracorporeal shock wave lithotripsy in an 8-month-old infant]

An 8-month-old boy who presented with pyrexia and vomiting was referred to the pediatric clinic of Kitasato University Hospital. He was found to have hematuria, proteinuria and pyuria. Abdominal X-ray film showed calcification suggesting renal staghorn calculus in the bilateral kidneys. At 10-months and 11-months, we succeeded in treating him with extracorporeal shock wave lithotripsy (ESWL) without complications.

Regulatory properties of the integrated long terminal repeat of the feline immunodeficiency virus

To examine the regulatory properties of feline immunodeficiency virus (FIV) long terminal repeat (LTR) integrated into host chromatin, Crandell feline kidney cells were stably transfected with the FIV LTR that directs the bacterial chloramphenicol acetyltransferase (CAT) gene. Using these cells, we examined the effects of treatment with several chemical agents, infection with feline viruses, or transfection with effector plasmids expressing FIV gene products on FIV LTR-directed gene expression. Among them, treatment with the phorbol ester (a strong activator of protein kinase C), forskolin (an inducer of cyclic-AMP), 5-azacytidine (a DNA methylation antagonist), or infection with feline herpesvirus type 1 (FHV-1), resulted in induction of CAT activity in the cells. These results suggest that the integrated FIV LTR is stimulated by cellular transcriptional factors induced by phorbol ester, forskolin and FHV-1, and is also inactivated by DNA methylation. Furthermore, this permanent cell line can be used as a screening system of activators of the FIV LTR.

Hepatitis B virus-associated nephropathy: 17 year progression from onset to end-stage renal failure

Hepatitis B virus-associated nephropathy (HB nephropathy) was first described in 1971. There have been few reports on the long-term prognosis in children with HB nephropathy. A case is reported here of a child who presented with symptoms of acute glomerulonephritis at 12 years of age and progressed to end-stage renal failure 17 years after the clinical onset, in spite of the seroconversion of HB virus by formation of HBe antibody.

Detection of feline immunodeficiency virus transcripts by quantitative reverse transcription-polymerase chain reaction

We developed a quantitative reverse transcription-polymerase chain reaction (RT-PCR) procedure to estimate replication status of feline immunodeficiency virus (FIV) in peripheral blood mononuclear cells (PBMCs) of cats. Primers used for the RT-PCR were designed to detect only multiple spliced transcripts of FIV and allowed us to detect the specific transcripts with high specificity. By using limiting-cell-dilution RT-PCR, we demonstrated that the specific transcripts were quantitatively detected in a single infected cell in a background of 1 x 10(6) uninfected cells without Southern blot hybridization. Furthermore, the transcripts were observed efficiently in all PBMCs of the chronically FIV-infected cats when examined by this RT-PCR technique. There results demonstrated that this RT-PCR method is applicable for specific detection of the FIV-specific transcripts in the PBMCs and for estimation of the viral replication status in vivo.

Temporal patterns of feline immunodeficiency virus transcripts in peripheral blood cells during the latent stage of infection

We have investigated the in vivo state of feline immunodeficiency virus (FIV) transcription in peripheral blood mononuclear cells (PBMC) of chronically FIV-infected, asymptomatic cats. FIV was detected in a high percentage of PBMC but not in the plasma of these cats. By quantitative reverse transcription-PCR (RT-PCR) analysis. FIV transcriptional status in the PBMC was characterized by extremely low or undetectable levels of unspliced or singly spliced mRNAs and predominantly multiply spliced mRNAs. Upon stimulation in vitro, however, the larger mRNA species and infectious virus production were rapidly induced in the PBMC. Furthermore, we demonstrated that viral production was induced in association with differential increases in the levels of each multiply spliced mRNA coding for FIV regulatory proteins. From these results, we suggest that replication of FIV is blocked at an early stage of gene expression in vivo, as described in asymptomatic human immunodeficiency virus (HIV) -infected patients, and that FIV infection in cats may be a useful model for clinical latency of HIV infection in man. Moreover, we propose that the replication of FIV in vivo may be controlled by the differential expression of each multiply spliced mRNA.

Quantification of feline immunodeficiency virus (FIV) proviral DNA in peripheral blood mononuclear cells of cats infected with Japanese strains of FIV

The polymerase chain reaction (PCR) method was applied for measurement of the proviral DNA copy number of feline immunodeficiency virus (FIV) in peripheral blood mononuclear cells (PBMC) of cats experimentally and naturally infected with FIV. In experimentally infected cats except one cat infected with the Petaluma strain, FIV-specific DNAs were efficiently amplified with the PCR method under the conditions used in this study. In the naturally FIV-infected cats, the specific DNAs were also amplified. We established a quantitative method for measurement of proviral DNA copy number in PBMC from cats infected with TM2-type of FIV strains, and found that the number was variable among the six cats examined, ranging from 10(4.0) to 10(5.7) copies per 10(5) PBMCs. This method can be applicable to cats naturally infected with FIV of TM2-type. Proviral DNA quantitation developed here could be useful as an additional parameter to evaluate the relationships among the proviral load, immune response and development of the clinical symptoms, and to monitor efficacy of antiviral therapy in vivo.

The C/EBP site in the feline immunodeficiency virus (FIV) long terminal repeat (LTR) is necessary for its efficient replication and is also involved in the inhibition of FIV LTR-directed gene expression by pseudorabies virus ICP4

We investigated effects of site-specific mutation of the putative C/EBP binding site in the feline immunodeficiency virus (FIV) long terminal repeat (LTR) on the basal promoter activity in Crandell feline kidney (CRFK) cells and on replication efficiency in CRFK cells and a T-lymphoblastoid cell line, MYA-1 cells. Mutation of the C/EBP site reduced the basal promoter activity in CRFK cells and prevented efficient FIV replication in both CRFK and MYA-1 cells. Gel-mobility-shift assay using nuclear extracts from CRFK and MYA-1 cells revealed that the nuclear factor(s) actually binds to the C/EBP site, but there was a clear difference in the binding patterns to the C/EBP site between CRFK and MYA-1 cell nuclear proteins. Furthermore, we demonstrated that the C/EBP site is necessary for inhibition of FIV LTR-directed gene expression by pseudorabies virus (PRV) ICP4. The C/EBP site is sufficient to confer inhibitory effect by PRV ICP4 on heterologous promoters. These data suggest that the C/EBP site in the FIV LTR is important for the positive regulation of FIV gene expression and replication and is also required for the negative regulation of FIV gene expression by PRV ICP4.

Establishment of carrier-state infection of a feline renal cell line with feline syncytial virus

Although feline syncytial virus (FSV) is normally highly cytopathogenic in Crandell feline kidney cells, a non-cytopathic persistent infection was established in the cells after cocultivation of the initially infected cells with uninfected cells 4 times. More than 90% of the persistently infected cells were positive for FSV antigen, and electron microscopy showed that the culture produced morphologically normal FSV. Virus from the carrier culture was infectious, however, the titer of the virus from the culture was lower than that from the cytocidally infected CRFK cells.

Seroepidemiological survey of feline retrovirus infections in cats in Taiwan in 1993 and 1994

In order to investigate the prevalence of infections with three feline retroviruses feline immunodeficiency virus (FIV), feline leukemia virus (FeLV) and feline syncytial virus (FSV) in Taiwan, we collected a total of 75 blood samples from cats from veterinary hospitals, a breeding cattery and a homeless shelter in 1993 and 1994. We examined the presences of anti-FIV and FSV antibodies and FeLV-p27 antigen in these samples by the indirect immunofluorescence and/or enzyme-linked immunosorbent assays. All of the serum samples positive for FIV were obtained from homeless cats and the overall FIV positive rate was 4%. The overall positive rates of FSV and FeLV were 28% and 1.3%, respectively. From these results, together with previous seroepidemiological surveys by others, it was revealed that the prevalence of FIV and FeLV infections appeared to be lower in Taiwan than in the United States or Japan. In contrast, the prevalence of FSV infection in Taiwan was as high as that in Japan.

Phylogenetic analysis of the long terminal repeat of feline immunodeficiency viruses from Japan, Argentina and Australia

The nucleotide sequences of the long terminal repeat of five Japanese, five Argentine and three Australian isolates of feline immunodeficiency virus (FIV) were determined and compared with those of isolates previously described. The results revealed that the Japanese isolates were found to cluster with nucleotide sequence similarity of 95.6%-99.4%. The Australian isolates also clustered with nucleotide sequence similarity of 97.2%-99.4%. The Argentine isolates formed two groups; the LP9 isolate is closely related to the Japanese isolates, whereas the LP1, LP3, LP20 and LP24 isolates are distant from both the Japanese and Australian isolates. From these results, FIV can be divided into three groups, namely: (I) the Californian, Australian and British isolates; (II) the Japanese isolates and one Argentine LP9 isolate; (III) the other Argentine isolates.

The molecular cloning and sequence of an open reading frame encoding for non-structural proteins of feline calicivirus F4 strain isolated in Japan

The nucleotide sequence of the 5'-end of feline calicivirus (FCV) Japanese F4 strain genome was determined. This region had 5311 bases and contained a large open reading frame (ORF1) encoding the non-structural proteins. The nucleotide sequence of the ORF1 region was highly conserved as compared with that of FCV F9 strain. When the deduced amino acid sequence of the ORF1 was compared with those of FCV F9 and CFI strains, the sequence was also highly conserved (88.9% and 88.8%, respectively). Functional motifs of the non-structural proteins were common to these strains. There were 2C polypeptide-, 3C cysteine protease- and 3D RNA-dependent RNA polymerase-like regions. The N-terminal region of 2C-like region continued upstream from the region identified by Neill [Virus Res. 17: 145-160]. Furthermore, the presence of 2B-like region was suggested in the upper stream of the 2C-like region, although the function of the region is unknown. When Kyte and Dolittle hydrophobicity profiles of the predicted amino acid sequences of the ORF1s of FCV F4 and F9 were computed and compared, both the profiles had striking similarities. In the region between residues 950-1000, there was a high rate of basic amino acid residues, suggesting that the polypeptide in this region of FCV may have a nucleic acid-binding function.

Comparative functional analysis of the various lentivirus long terminal repeats in human colon carcinoma cell line (SW480 cells) and feline renal cell line (CRFK cells)

Basal promoter activities of various lentiviral long terminal repeats (LTRs) in a human colon carcinoma cell line (SW480 cells) and a feline renal cell line (CRFK cells) were examined by the chloramphenicol acetyltransferase (CAT) assay using the LTR-CAT reporter plasmids. In SW480 cells, the basal promoter activities induced by LTRs of visna virus, caprine arthritis-encephalitis virus (CAEV), and simian immunodeficiency virus (SIVAGM) were moderate, and those induced by LTRs of human immunodeficiency virus (HIV) type 1 (HIV-1) and HIV type 2 (HIV-2) were low. However, the activity induced by the LTR of feline immunodeficiency virus (FIV) was extremely low. In CRFK cells, the basal promoter activities induced by LTRs of visna virus, CAEV and SIVAGM were relatively high, and those induced by LTRs of HIV-1, HIV-2 and FIV were moderate. From these data, although the structure of the LTR of FIV is reported to be similar to that of visna virus and CAEV, the function of the LTR of FIV is rather quite different from that of the LTR of these viruses.

Inhibition of feline immunodeficiency virus gene expression and replication by alphaherpesvirus ICP4 homologues

We investigated the effects of pseudorabies virus (PRV), herpes simplex virus type 1 (HSV-1), and equine herpesvirus type 1 (EHV-1) ICP4 homologues on feline immunodeficiency virus (FIV) long terminal repeat (LTR)-directed gene expression. This was done by using the transient expression chloramphenicol acetyltransferase (CAT) assay in Crandell feline kidney (CRFK) and Felis catus whole fetus 4 cells transfected with a chimeric FIV LTR-CAT reporter construct in combination with effector plasmids expressing the PRV, HSV-1 or EHV-1 ICP4 homologue. The experiments demonstrated that the ICP4 homologues could significantly inhibit FIV LTR-directed gene expression. Moreover, the ICP4 homologues also exhibited a marked inhibitory effect on FIV replication in CRFK cells cotransfected with an infectious molecular clone of FIV.

The genome of feline immunodeficiency virus

Feline immunodeficiency virus (FIV) is a member of the genus Lentivirus of the family Retroviridae. FIV can infect T lymphocytes and monocytes/macrophages in vitro and in vivo, and causes an acquired immunodeficiency syndrome-like disease in cats. Several isolates of FIV from geographically distant countries have been molecularly cloned. There is considerable heterogeneity especially in Env gene among the FIV isolates and they can be divided into two or more subgroups. Like other lentiviruses, FIV has a complex genome structure. Gag gene encodes matrix, capsid and nucleocapsid proteins, and Pol gene encodes protease, reverse transcriptase, dUTPase and integrase. The dUTPase is not present in the primate lentiviruses but present in the non-primate lentiviruses. Env gene encodes surface and transmembrane envelope glycoproteins. In addition to the structural and enzymatic proteins, at least three more genes (Vif, ORF A, Rev) are present in FIV. Vif is related to the infectivity of the cell-free viruses. Rev functions in the stability and transport of incompletely spliced viral RNAs from the nucleus to cytoplasm and is indispensable for virus replication. Although the Tat protein of the primate lentiviruses is essential for virus replication, ORF A (putative Tat gene) of FIV is not essential for virus replication in established feline T lymphoblastoid cell lines. However, the ORF A gene product is related to the efficient replication of the virus in primary peripheral blood lymphocytes. In the long terminal repeat (LTR) of FIV, there are many putative binding sites for enhancer/promoter proteins. Among these binding sites, the putative AP-1 site is important for basal promoter activity of the LTR and responsible for the T cell activation signal through protein kinase C, however the site is not required for the virus replication in established feline T lymphoblastoid cell lines. Comparative study of the molecular biology of lentiviruses revealed that the genome structure, splicing pattern and functional enhancer protein-binding sites of FIV are more similar to those of the ruminant lentiviruses than those of the primate lentiviruses.

Comparison of biological properties of feline immunodeficiency virus isolates using recombinant chimeric viruses

The biological properties of homogeneous populations of feline immunodeficiency viruses derived from infectious, molecular clones of the TM1, TM2 and Petaluma strains were compared. Differences in infectivity for Crandell feline kidney (CRFK) cells, and in syncytium formation and replication kinetics in a feline T lymphoblastoid cell line (MYA-1 cells) were observed. To investigate the basis of these differences between the TM2 and Petaluma strains, we first compared the basal promoter activity of the long terminal repeat which is a highly divergent region, but no significant difference in activities was found in CRFK cells. We then constructed two recombinant chimeric clones which carry gag, pol, vif, and ORF A from the heterologous virus. From analyses using the chimeric clones, it was revealed that efficient virus growth in CRFK cells and MYA-1 cells was regulated by the gag, pol, vif and ORF A regions, whereas viral determinants of infectivity for CRFK cells, and syncytium formation and cytopathogenicity in MYA-1 cells, were located in the env region.

Comparison of the Rev transactivation of feline immunodeficiency virus in feline and non-feline cell lines

The Rev protein of feline immunodeficiency virus (FIV) differentially transactivates the expression of viral structural proteins by allowing the accumulation of unspliced and singly spliced viral mRNA in cytoplasm via the Rev response element (RRE) at the end of env. To investigate the role of rev gene of FIV for the virus life cycle and cell tropism, we constructed the Rev expression plasmids, and functional activity of the Rev was assayed by using chloramphenicol acetyltransferase (CAT) assay system in feline and non-feline cell lines. Although the FIV Rev protein showed high transactivity to result in enhanced CAT production in a feline cell line, the productions of the CAT in non-feline cell lines were significantly lower than that in the feline cell line. These results indicate that specific cellular factor(s) present in feline cell line is required for the FIV Rev full-action and also suggest that the Rev action plays one of the important roles in determining the FIV cell tropism.

Effects of insertion of multiple AP-1 binding sites into the U3 region of the long terminal repeat of feline immunodeficiency virus

An oligonucleotide containing multiple AP-1 binding sites was introduced into the regulatory sequence in the long terminal repeat (LTR) of feline immunodeficiency virus (FIV). Chloramphenicol acetyltransferase assay revealed that basal promoter activity of the mutated LTR was higher than that of the wild-type LTR in Crandell feline kidney (CRFK) cells. The mutated LTR was introduced into an infectious molecular clone of FIV and the clone was transfected into CRFK cells. The virus production of the mutant in the cells was as high as that of the wild-type when determined by the reverse transcriptase activity assay. The growth of the mutant virus obtained from the transfected CRFK cells was examined in feline T lymphoblastoid cell lines (MYA-1 and FeL-039 cells) and primary feline peripheral blood mononuclear cells (fPBMCs). The growth was delayed when compared with that of the wild-type virus in all the cells used. Upon examination by polymerase chain reaction, the length of the LTR of the mutant virus was shortened in both MYA-1 cells and fPBMCs. Sequence analysis revealed that the insertion was completely deleted 39 days after infection in the MYA-1 cells.

Feline immunodeficiency virus gene expression: analysis of the RNA splicing pattern and the monocistronic rev mRNA

The transcription pattern of the feline immunodeficiency virus (FIV) genome in a feline CD4+ cell line was examined. In addition to the genomic RNA (9.2 kb), at least five FIV-specific transcripts [5.2, 4.4 (doublet), 1.7 and 1.4 kb] were detected by using subgenomic restriction enzyme fragments of an FIV molecular clone or FIV-specific oligonucleotides as probes. Among these transcripts, the 9.2, 5.2 and 4.4 (doublet) kb mRNAs were not expressed in the cytoplasm of cells transfected with a rev- mutant. To determine the location of splice junctions in the FIV genome, we used PCR to amplify and clone cDNAs corresponding to the viral mRNAs from infected cells. The region between pol and env was found to contain at least two splice donor and three splice acceptor sites. Two splice acceptor sites were detected in the 3' region of env. By hybridization analysis and sequencing of cDNA clones, it was revealed that the medium sized mRNAs are derived from a single splice event, with different splice acceptor sites, and that the two smaller transcripts are doubly or triply spliced mRNAs. Our results demonstrate a complex pattern of alternative splicing of FIV mRNAs. Furthermore, we identified monocistronic rev mRNA species that employ a unique splice acceptor site.

Antigenic analysis of feline calicivirus capsid precursor protein and its deleted polypeptides produced in a mammalian cDNA expression system

An entire open reading frame in a cDNA encoding the capsid protein gene of feline calicivirus (FCV) was subcloned into a mammalian expression vector. After transfection of the constructed plasmid (pMCV-II) into COS-7 cells, the expressed protein was detected by indirect immunofluorescence assay (IFA) using a panel of monoclonal antibodies (MAbs) to the capsid protein of FCV. All of the MAbs reacted with the transfected COS-7 cells in IFA. The 76 kDa capsid precursor protein was demonstrated in an immunoblot analysis, indicating that the translated precursor protein was not processed into the matured capsid protein in this expression system. Two in-frame deleted and a frameshift mutated cDNAs were generated by using restriction sites within the capsid protein coding sequence in pMCV-II to analyze the antigenic sites of the protein. The results of IFA using the MAbs and COS-7 cells transfected with the deleted or mutated cDNAs suggested that three neutralizing epitopes had a conformational nature and that the other four linear epitopes were related to 74 amino acid residues between positions 381 and 454 in the protein, in which high variation was known to be present among three strains of FCV.

The feline immunodeficiency virus ORF-A gene facilitates efficient viral replication in established T-cell lines and peripheral blood lymphocytes

Frameshift mutants corresponding to all of the identified open reading frames of feline immunodeficiency virus, including the ORF-A gene, which has an unknown function, were constructed in vitro. Upon transfection into cells, no significant difference between the phenotypes of ORF-A mutant clones and those of wild-type clones was demonstrated. Although only ORF-A mutant virus among all mutant viruses from transfected cells showed infectivity in established T-cell lines, the replication and propagation of the ORF-A mutant virus were efficiently reduced compared with those of the wild-type virus. Moreover, the loss of the function of the ORF-A gene resulted in a severe defect in productive infection in primary peripheral blood lymphocytes both in the amount of reverse transcriptase activity produced and in core protein expression. These findings demonstrate that the ORF-A gene of feline immunodeficiency virus is required for efficient viral replication and suggest that the ORF-A gene is likely to be important for natural infection.

Localization of the viral antigen of feline immunodeficiency virus in the lymph nodes of cats at the early stage of infection

Immunohistochemical examinations of localization of feline immunodeficiency virus (FIV) Gag protein were performed on lymph nodes of cats experimentally inoculated with three different strains of FIV (infectious molecular clone of TM 1, Petaluma, and KYO-1 strains), using rabbit anti-FIV Gag serum. The FIV Gag antigens were observed in many follicular dendritic cells (FDCs) and sparsely in small lymphocytes of paracortical area in the lymph nodes of cats inoculated with Petaluma and KYO-1 strains. However, the antigens were present only in small lymphocytes, and not in FDCs of a cat inoculated with infectious molecular clone of the TM1 strain. The cell type differences in expression of the viral antigen in vivo might reflect on the cell tropisms of the FIV strains in vitro. By double immunohistochemical staining with rabbit anti-FIV Gag serum and monoclonal antibodies which recognize feline CD4, feline CD8 or feline pan-T molecules, the FIV Gag-positive lymphocytes were characterized as feline CD4-positive T cells. Since the distributions of FIV Gag antigens were mainly in the FDCs, the FDCs may play an important role as a major reservoir and may be a primary target of FIV at early stages of infection.