Advances in the treatment of cytomegalovirus

BACKGROUND

Human cytomegalovirus (HCMV) is a threat to immunologically weak patients. HCMV cannot yet be eliminated with a vaccine, despite recent advances.

SOURCES OF DATA

Sources of data are recently published research papers and reviews about HCMV treatments.

AREAS OF AGREEMENT

Current antivirals target the UL54 DNA polymerase and are limited by nephrotoxicity and viral resistance. Promisingly, letermovir targets the HCMV terminase complex and has been recently approved by the FDA and EMA.

AREAS OF CONTROVERSY

Should we screen newborns for HCMV, and use antivirals to treat sensorineural hearing loss after congenital HCMV infection?

GROWING POINTS

Growing points are developing drugs against latently infected cells. In addition to small molecule inhibitors, a chemokine-based fusion toxin protein, F49A-FTP, has shown promise in killing both lytically and latently infected cells.

AREAS TIMELY FOR DEVELOPING RESEARCH

We need to understand what immune responses are required to control HCMV, and how best to raise these immune responses with a vaccine.

LPS promotes a monocyte phenotype permissive for human cytomegalovirus immediate-early gene expression upon infection but not reactivation from latency

Human cytomegalovirus (HCMV) infection of myeloid cells is closely linked with the differentiation status of the cell. Haematopoietic progenitors and CD14+ monocytes are usually non-permissive for lytic gene expression which can lead to the establishment of latent infections. In contrast, differentiation to macrophage or dendritic cell (DC) phenotypes promotes viral reactivation or renders them permissive for lytic infection. The observation that high doses of Lipopolysaccharide (LPS) drove rapid monocyte differentiation in mice led us to investigate the response of human monocytes to HCMV following LPS stimulation in vitro. Here we report that LPS triggers a monocyte phenotype permissiveness for lytic infection directly correlating with LPS concentration. In contrast, addition of LPS directly to latently infected monocytes was not sufficient to trigger viral reactivation which is likely linked with the failure of the monocytes to differentiate to a DC phenotype. Interestingly, we observe that this effect on lytic infection of monocytes is transient, appears to be dependent on COX-2 activation and does not result in a full productive infection. Thus LPS stimulated monocytes are partially permissive lytic gene expression but did not have long term impact on monocyte identity regarding their differentiation and susceptibility for the full lytic cycle of HCMV.

Transient activation of human cytomegalovirus lytic gene expression during latency allows cytotoxic T cell killing of latently infected cells

Human cytomegalovirus (HCMV) latency in the myeloid lineage is maintained by repressive histone modifications around the major immediate early promoter (MIEP), which results in inhibition of the lytic viral life cycle. We now show that pharmacological inhibition of histone deacetylases (HDACs) relieves this repression of the MIEP and induces transient expression of the viral lytic immediate early (IE) antigens but, importantly, not full virus reactivation. In turn, these latently infected cells now become targets for IE-specific cytotoxic T cells (CTLs) which are present at high frequency in all normal healthy HCMV positive carriers but would normally be unable to target latent (lytic antigen-negative) cells. This approach of transiently inducing viral lytic gene expression by HDAC inhibition, in otherwise latently infected cells, offers a window of opportunity to target and purge the latent myeloid cell reservoir by making these normally immunologically undetectable cells visible to pre-existing host immune responses to viral lytic antigens.

Trace metals and degenerative diseases of the skeleton

Aluminum related osteodystrophy is the most important manifestation of trace metal toxicity related to degenerative diseases of the skeleton. Aluminum overload occurs in chronic renal failure patients on hemodialysis treatment and results from transfer from dialysis solutions and from oral intake of aluminum containing phosphate binding gels. Laboratory diagnosis involves serum and bone analysis and bone staining for aluminum. A challenge test with desferrioxamine also aids in the diagnosis. Electrothermal atomic absorption spectrometry is widely used for aluminum detection. Guidelines for toxic concentrations of aluminum have been established.

The diagnostic value of faecal trypsin estimation in chronic pancreatic disease

Faecal trypsin levels have been estimated by a photometric azo-casein method in 242 children and 45 adults. Analysis of the results shows that this is not a specific test of pancreatic dysfunction but that it appears to be a useful screening test for the selection of patients who may have severe pancreatic disease and on whom further specific investigations should be performed.

Comparison of biochemical with radiological findings in renal osteodystrophy

In a group of 121 adult patients with end-stage chronic renal failure who had been undergoing maintenance haemodialysis for up to 10 years a number of biochemical variables have been measured and related to a set of objective radiological changes in the same patients. The changes in plasma calcium, magnesium, phosphate, total protein, and albumin concentration did not distinguish the patients who were grouped on a radiological basis. Plasma alkaline phosphatase activity increased with the severity of the radiological findings but did not provide a sensitive discriminatory index between the different radiological groups. Plasma hydroxyproline concentration was found to be more sensitive than plasma alkaline phosphatase activity in detecting a radiological abnormality in some of the patients.

Effects of Chlamydia trachomatis infection on the expression of natural killer (NK) cell ligands and susceptibility to NK cell lysis

Natural killer (NK) cells are an important component of the immediate immune response to infections, including infection by intracellular bacteria. We have investigated recognition of Chlamydia trachomatis (CT) by NK cells and show that these cells are activated to produce interferon (IFN)-gamma when peripheral blood mononuclear cells (PBMC) are stimulated with CT organisms. Furthermore, infection of epithelial cell lines with CT renders them susceptible to lysis by human NK cells. Susceptibility was observed 18-24 h following infection and required protein synthesis by the infecting chlamydiae, but not by the host cell; heat or UV inactivated chlamydiae did not induce susceptibility to NK cell lysis. CT infection was also shown to decrease the expression of classical and non-classical major histocompatibility complex (MHC) molecules on infected cells, thus allowing recognition by NK cells when combined with an activating signal. A candidate activating signal is MICA/B, which was shown to be expressed constitutively on epithelial cells.

Latency and reactivation of human cytomegalovirus

The sequence analysis of herpesviruses suggests they have been evolving with their individual vertebrate hosts for millions of years, and their divergence parallels that of the hosts they infect. Given this time they have been learning to live with their individual hosts, it is not surprising that they have become extremely well adapted to doing so without causing much in the way of obvious disease. A key feature of their strategy for persisting in the host is the ability of all herpesviruses to establish latent infection-a state in which no, or only a very limited set of, viral genes are expressed in cells in which viral DNA persists. The alpha herpesviruses (herpes simplex and varicella zoster virus) establish latency in neuronal cells in sensory ganglia: these are long lived non-dividing cells and the alpha herpesviruses persist in these with expression of only the latency associated transcripts-although the function of these RNA transcripts remains incompletely understood. The principal gamma herpesvirus of humans, Epstein Barr virus (EBV), is latent mainly in B lymphocytes: EBV persistence in B cells is associated with expression of a limited set of viral genes encoding functions necessary for the maintenance of the episomal viral DNA as B cells divide.The mechanism by which the principal beta herpesvirus of humans-human cytomegalovirus (HCMV) persists, is also incompletely understood and the subject of this review. Understanding how HCMV persists has clinical relevance in that its transmission to seronegative recipients might be more easily prevented, and the mechanisms by which it produces disease in the neonate and immunocompromised hosts more easily understood, if we knew more about the cells in which the virus is latent and the way in which it reactivates.

Vaccines against persistent DNA virus infections

Persistent viruses present some particular problems for vaccine design. As for acute non-persistent viruses, the prime goal of a vaccine should be to prevent primary infection. Vaccines might also be used to modify the course of established persistent virus infections - so-called postinfective immunisation. This chapter deals with selected persistent DNA viruses, in particular the human herpes viruses.

Functional heterogeneity and high frequencies of cytomegalovirus-specific CD8(+) T lymphocytes in healthy seropositive donors

Human cytomegalovirus (HCMV) infection is largely asymptomatic in the immunocompetent host, but remains a major cause of morbidity in immunosuppressed individuals. Using the recently described technique of staining antigen-specific CD8(+) T cells with peptide-HLA tetrameric complexes, we have demonstrated high levels of antigen-specific cells specific for HCMV peptides and show that this may exceed 4% of CD8(+) T cells in immunocompetent donors. Moreover, by staining with tetramers in combination with antibodies to cell surface markers and intracellular cytokines, we demonstrate functional heterogeneity of HCMV-specific populations. A substantial proportion of these are effector cytotoxic T lymphocytes, as demonstrated by their ability to lyse peptide-pulsed targets in "fresh" killing assays. These data suggest that the immune response to HCMV is periodically boosted by a low level of HCMV replication and that sustained immunological surveillance contributes to the maintenance of host-pathogen homeostasis. These observations should improve our understanding of the immunobiology of persistent viral infection.

Large clonal expansions of human virus-specific memory cytotoxic T lymphocytes within the CD57+ CD28- CD8+ T-cell population

The proportion of human peripheral blood CD8+ T cells that are CD57+ CD28- is low at birth but increases with age and in individuals infected with human cytomegalovirus (HCMV) or human immunodeficiency virus (HIV). These CD57+ CD28- CD8+ T cells contain large oligoclonal T-cell expansions whose antigen specificity is unknown. We identified clonal expansions of virus-specific memory cytotoxic T-lymphocyte precursors (CTLp) in both healthy carriers of HCMV and in asymptomatic HIV-infected subjects. In each subject, from the T-cell receptor (TCR) beta-chain hypervariable sequence of each immunodominant CTL clone, we designed complementary oligonucleotide probes to quantify the size and phenotypic segregation of individual virus-specific CTL clones in highly purified populations of peripheral blood CD8+ T cells. We found large clonal expansions of virus-specific CTL clonotypes in CD57+ CD28- CD8+ T cells. Using limiting dilution analysis, we found functional peptide-specific CTLp at high frequency in CD57+ CD28- cells. Thus, memory CTL specific for persistent viruses account for many oligoclonal expansions within CD57+ CD28- CD8+ T cells.

Human virus-specific CD8+ CTL clones revert from CD45ROhigh to CD45RAhigh in vivo: CD45RAhighCD8+ T cells comprise both naive and memory cells

It has been generally believed that human CD8+ memory cells are principally found within the CD45ROhigh population. There are high frequencies of CD8+ memory CTL specific for the human CMV tegument phosphoprotein pp65 in PBMC of long-term virus carriers; the large population of memory CTL specific for a given pp65 peptide contains individual CTL clones that have greatly expanded. In this study, we found high frequencies of pp65 peptide-specific memory CTL precursors in the CD45ROhighCD45RA- population, but also appreciable frequencies in the CD45RAhigh subpopulation. Because the majority of CD8+ T cells in PBMC are CD45RAhigh, more of the total pp65-specific memory CTL pool is within the CD45RAhigh than in the CD45ROhigh compartment. Using clonotypic oligonucleotide probes to quantify the size of individual pp65-specific CTL clones in vivo, we found the CD45RAhigh population contributed 6- to 10-fold more than the CD45ROhigh population to the total virus-specific clone size in CD8+ cells. During primary CMV infection, an individual virus-specific CTL clone was initially CD45ROhigh, but after resolution of infection this clone was detected in both the CD45ROhigh and the CD45RAhigh populations. We conclude that CD45RA+ human CD8+ T cells do not solely comprise naive cells, but contain a very significant proportion of memory cells, which can revert from the CD45ROhigh to CD45RAhigh phenotype in vivo.

Human CD28-CD8+ T cells contain greatly expanded functional virus-specific memory CTL clones

At birth, almost all human peripheral blood CD8+ T cells express the costimulatory molecule CD28. With increasing age, the proportion of CD8+ T cells that lack CD28 increases. Because the Ag specificity of CD28-CD8+ T cells has not previously been defined, we studied the contribution of CD28-CD8+ T cells to the memory CD8+ CTL response against two human persistent viruses, human CMV (HCMV) and HIV. From PBMC of healthy virus carriers we generated multiple independent CTL clones specific for defined viral peptides and sequenced their TCR beta-chains. We designed clonotypic oligonucleotides complementary to each beta-chain hypervariable sequence and quantified the size of individual immunodominant CTL clones in PBMC. Some individual CTL clones were very large, comprising up to 3.1% of all CD8+ T cells in PBMC, and were generally maintained at a stable level for months. Individual virus-specific CTL clones were consistently more abundant in purified CD28- cells than in the CD8+ population as a whole. Because CD28-CD8+ cells as a population have been reported to proliferate poorly in response to mitogen, we studied the function of these virus-specific CD28- CTL clones by quantifying the frequency of peptide-specific CTL precursors using limiting dilution analysis. CD28-CD8+ T cells contained high frequencies of functional memory CTL precursors specific for peptides of HCMV or HIV, generally higher than in the CD8+ T cell population as a whole. We conclude that in asymptomatic HCMV and HIV infection, human CD28-CD8+ T cells contain high frequencies of functional virus-specific memory CTL clones.

The memory cytotoxic T-lymphocyte (CTL) response to human cytomegalovirus infection contains individual peptide-specific CTL clones that have undergone extensive expansion in vivo

Human cytomegalovirus (HCMV)-specific CD8(+) cytotoxic T lymphocytes (CTL) appear to play an important role in the control of virus replication and in protection against HCMV-related disease. We have previously reported high frequencies of memory CTL precursors (CTLp) specific to the HCMV tegument protein pp65 in the peripheral blood of healthy virus carriers. In some individuals, the CTL response to this protein is focused on only a single epitope, whereas in other virus carriers CTL recognized multiple epitopes which we identified by using synthetic peptides. We have analyzed the clonal composition of the memory CTL response to four of these pp65 epitopes by sequencing the T-cell receptors (TCR) of multiple independently derived epitope-specific CTL clones, which were derived by formal single-cell cloning or from clonal CTL microcultures. In all cases, we have observed a high degree of clonal focusing: the majority of CTL clones specific to a defined pp65 peptide from any one virus carrier use only one or two different TCRs at the level of the nucleotide sequence. Among virus carriers who have the same major histocompatibility complex (MHC) class I allele, we observed that CTL from different donors that recognize the same peptide-MHC complex often used the same Vbeta segment, although other TCR gene segments and CDR3 length were not in general conserved. We have also examined the clonal composition of CTL specific to pp65 peptides in asymptomatic human immunodeficiency virus-infected individuals. We have observed a similarly focused peptide-specific CTL response. Thus, the large population of circulating HCMV peptide-specific memory CTLp in virus carriers in fact contains individual CTL clones that have undergone extensive clonal expansion in vivo.

Reversal by desferrioxamine of tau protein aggregates following two days of treatment in aluminum-induced neurofibrillary degeneration in rabbit: implications for clinical trials in Alzheimer's disease

A clinical trial in patients with Alzheimer's disease has indicated that frequent intramuscular (i.m.) treatment with desferrioxamine (DFO) slows progression of the disease. Confirmatory trials have not been carried out, partly because of the rigors of twice daily intramuscular injections over a period of 2 years, even though the initial report gave promising results. The aim of the present study was to determine an optimal DFO treatment protocol in an animal model exhibiting Alzheimer's-like intraneuronal protein aggregates, previously shown to be partially reversed by such treatment. New Zealand white rabbits were injected intracisternally with either aluminum (Al) maltolate or with saline on day 0. Intramuscular injections of DFO were given to selected rabbits for 2 days prior to sacrifice on days 4, 6 or 8. Bielschowsky's silver impregnation demonstrated widespread neurofibrillary degeneration (NFD) in neuronal cell bodies and neurites of brain and spinal cord from Al-treated rabbits. Monoclonal antibodies Tau-2, AT8, PHF-1 and Alz-50, all of which characteristically stain neurofibrillary tangles associated with Alzheimer's disease, strongly labeled the Al-induced NFD. The number of positive neurons and staining intensities were much less in rabbits treated with Al and subsequently with DFO, than in animals only given Al. Control rabbit receiving intracisternal saline were negative for NFD. The results of quantitative immunohistochemistry using image analysis confirmed that immunostaining densities with all tau mAbs were higher in Al-treated than in Al-DFO-treated or in saline-treated controls. Furthermore, it appears that hyperphosphorylation of tau does not make this protein resistant to degradation once Al has been removed by DFO treatment. The effectiveness of only two days of DFO treatment in reversing Al-induced neurofibrillary degeneration suggests that further clinical trials of DFO for treatment of Alzheimer's disease should be attempted using much less frequent administration of DFO than in the initial study (Crapper McLachlan et al., 1991).

Neurofibrillary lesions in experimental aluminum-induced encephalopathy and Alzheimer's disease share immunoreactivity for amyloid precursor protein, A beta, alpha 1-antichymotrypsin and ubiquitin-protein conjugates

Neurofibrillary tangles of Alzheimer's disease contain predominantly tau protein and to a lesser degree amyloid precursor protein (APP), A beta protein, alpha 1-antichymotrypsin (ACT) and ubiquitin. Previously we have demonstrated the presence of phosphorylated tau and neurofilament proteins in neurofibrillary degeneration (NFD) induced by aluminum (Al) maltolate in rabbits [Savory et al., Brain Res. 669 (1995) 325-329; Savory et al., Brain Res. 707 (1996) 272-281]. Using the same animal system we have now detected APP, A beta, ACT and ubiquitin-like immunoreactivities in NFD-bearing neurons, often colocalizing in the NFD. Diffuse cytoplasmic staining for APP, A beta and ubiquitin was also present in neurons without NFD from Al maltolate-treated rabbits. This study provides additional support for immunochemical similarities between Al-induced NFD in rabbits and the neurofibrillary tangles in human subjects with Alzheimer's disease.

The human cytotoxic T-lymphocyte (CTL) response to cytomegalovirus is dominated by structural protein pp65: frequency, specificity, and T-cell receptor usage of pp65-specific CTL

Cytotoxic T lymphocytes (CTL) appear to play an important role in the control of human cytomegalovirus (HCMV) in the normal virus carrier: previous studies have identified peripheral blood CD8+ CTL specific for the HCMV major immediate-early gene product (IE1) and more recently, by bulk culture and cloning techniques, have identified CTL specific for a structural gene product, the lower matrix protein pp65. In order to determine the relative contributions of CTL which recognize the HCMV proteins IE1, pp65, and glycoprotein B (gB) to the total HCMV-specific CTL response, we have used a limiting-dilution analysis system to quantify HCMV-specific CTL precursors with different specificities, allowing the antigenic specificity of multiple short-term CTL clones to be assessed, in a group of six healthy seropositive donors. All donors showed high frequencies of HCMV-specific major histocompatibility complex-restricted CTL precursors. There was a very high frequency of CTL specific for pp65 (lower matrix protein); IE1-specific CTL were also detectable at lower frequencies in three of five donors, while CTL directed to gB were undetectable. A pp65 gene deletion mutant of HCMV was then used to estimate the contribution of pp65-specific CTL to the total HCMV-specific CTL response; this showed that between 70 and 90% of all CTL recognizing HCMV-infected cells were pp65 specific. Analysis of the peptide specificity of pp65-specific CTL showed that some donors have a highly focused response recognizing a single peptide; the T-cell receptor Vbeta gene usage in these two donors was shown to be remarkably restricted, with over half of the responding CD8+ T cells utilizing a single Vbeta gene rearrangement. Other subjects recognized multiple pp65 peptides: nine new pp65 CTL peptide epitopes were defined, and for five of these the HLA-presenting allele has been identified. All four of the HLA A2 donors tested in this study recognized the same peptide. This apparent domination of the CTL response to HCMV during persistent infection by a single structural protein, irrespective of major histocompatibility complex haplotype, is not clearly described for other persistent virus infections, and the mechanism requires further investigation.

Quantitative image analysis of temporal changes in tau and neurofilament proteins during the course of acute experimental neurofibrillary degeneration; non-phosphorylated epitopes precede phosphorylation

Perturbation of the neuronal cytoskeleton represents an integral feature of neurofibrillary tangles which are characteristic neuropathological findings seen in Alzheimer's disease. Microtubule associated protein tau (tau) is considered to be the major component of these lesions although neurofilament proteins also are present. The present study explores the formation of intraneuronal tau and neurofilament protein aggregates using intracisternal administration of aluminum maltolate to rabbits. The time course of the formation of these aggregates and subsequent phosphorylation have been investigated by immunohistochemical methods using a panel of monoclonal antibodies, with quantitation of the staining by image analysis. Neurofilament proteins begin to aggregate by day 1 following aluminum maltolate injection on day 0. Increases in non-phosphorylated neurofilament proteins are observed first, with phosphorylated epitopes being recognized by day 3. Tau follows a similar pattern in that non-phosphorylated epitopes appear to precede phosphorylation. The monoclonal antibody Alz-50 which recognizes a phosphorylation-independent epitope of tau in Alzheimer's disease paired helical filaments, demonstrates positivity in the aluminum maltolate-treated rabbits by day 3. Other tau monoclonal antibodies which recognize phosphorylated tau in paired helical filaments (AT8 and PHF-1) show positive immunostaining on days 6-8. These results indicate that intraneuronal aggregation of cytoskeletal proteins can be initiated by factors other than phosphorylation. However, phosphorylation occurring as a secondary event probably contributes to stabilization of the aggregates.

Passage of Japanese encephalitis virus in HeLa cells results in attenuation of virulence in mice

Of four wild-type strains (Nakayama-original, SA14, 826309 and Beijing-1) of Japanese encephalitis (JE) virus that were passaged six times in HeLa cells (HeLa p6), two (Nakayama-original and 826309) became attenuated for mice. In the case of strain Nakayama-original, the virulence for mice was markedly reduced and attenuation was retained on passage in primary chicken embryo fibroblast, LLC-MK2 and C6/36 cells. The binding of non-HeLa-passaged Nakayama virus to mouse brain membrane receptor preparations could be differentiated from binding by Nakayama HeLa p6 virus, suggesting that the envelope (E) protein is involved in the attenuated phenotype. Both of the attenuated viruses can be distinguished from the virulent non-HeLa-passaged parental viruses by examination with E protein reactive vaccine and wild-type-specific monoclonal antibodies (MAbs). The vaccine-specific MAb V23, which is only reactive with the SA14 series of live vaccine viruses, recognized the HeLa cell-attenuated Nakayama-original and 826309 viruses, whereas two wild-type-specific MAbs (MAbs K13 and K39) lost reactivity. Comparison of the nucleotide sequences of the structural protein genes of the 826309 and Nakayama-original virulent parent and attenuated HeLa p6 viruses revealed that the viruses differed by 37 and 46 nucleotides coding for eight and nine amino acid mutations, respectively. However, other than one amino acid in the E protein, the membrane and E protein amino acid sequences of the two attenuated HeLa p6 viruses were identical.

Hyperaluminemia associated with liver transplantation and acute renal failure

Iatrogenic aluminium toxicity is reported in a patient who underwent an orthotopic liver transplant and who had concomitant renal failure requiring hemodialysis. Following transplantation the patient developed a metabolic encephalopathy with only mildly elevated blood ammonia concentrations. During the period following transplantation the patient received massive infusions of albumin and was on oral feeding (vivonexten), both of which contained aluminium, as did the dialysis fluid. Hyperaluminemia and profoundly elevated liver tissue aluminium concentrations were observed. Treatment with desferrioxamine, a trivalent ion chelator, decreased the plasma aluminium concentrations with an improvement in the patient's mental status.

Tau immunoreactivity associated with aluminum maltolate-induced neurofibrillary degeneration in rabbits

Intracisternal administration of aluminum maltolate to rabbits produces a marked argyrophilic neurofibrillary degeneration (NFD) which is also immunoreactive for both phosphorylated and non-phosphorylated microtubule associated protein tau. Using tissue fixation in PBF, the monoclonal antibodies Tau-2 and AT8 stain the NFD. Dephosphorylation markedly reduces the positivity of AT8. Using PLP-fixed tissue, monoclonal antibody Tau-1 also immunostains aluminum-induced NFD.

Comparison of nucleotide and deduced amino acid sequence of the 5' non-coding region and structural protein genes of the wild-type Japanese encephalitis virus strain SA14 and its attenuated vaccine derivatives

Nucleotide sequences of the 5' non-coding region and the structural protein genes of the live, attenuated Japanese encephalitis vaccine virus strains SA14-2-8 and SA14-5-3 and the wild-type parental strain SA14/USA were determined. SA14-2-8 differed from SA14/USA by 13 nucleotides and eight amino acids whereas SA14-5-3 differed from SA14/USA by 15 nucleotides and eight amino acids. A comparison of the 5' non-coding region and amino acid sequences of the structural proteins of these two attenuated vaccine strains and of vaccine strains SA14-14-2/PHK and SA14-14-2/PDK with three sequences of their wild-type parent SA14 virus was performed. This revealed only two common amino acid substitutions at positions 138 and 176 in the envelope (E) protein. The substitution at E138 was predicted to cause a change in the secondary structure of the E protein. These two amino acid substitutions in the E protein may contribute to attenuation of the Japanese encephalitis vaccine viruses.

Partial reversal of aluminium-induced neurofibrillary degeneration by desferrioxamine in adult male rabbits

Desferrioxamine, a chelating agent with a high affinity for aluminium, has been reported to slow the clinical progression of dementia associated with Alzheimer's disease [4]. We report here the effects of desferrioxamine treatment on aluminium-induced neurofibrillary degeneration in rabbits. Adult male New Zealand white rabbits received a single injection of aluminium-maltolate into the lateral cerebral ventricle. Three days later, one group of rabbits was treated with intramuscular injections of desferrioxamine twice daily; a second group received saline instead of desferrioxamine. Both groups were sacrificed 4 or 5 days following initiation of desferrioxamine or saline treatment. Minimal neurofibrillary degeneration was found in two of six desferrioxamine-treated rabbits, while all six rabbits treated with saline showed extensive neurofibrillary degeneration, particularly in the ventral horn of the lower spinal cord. Quantitation of the neurofibrillary degeneration in ventral horn neurons of lumbar cord revealed 30% to be affected in saline-treated animals compared to zero-affected neurons following desferrioxamine treatment. When sacrificed just 3 days after aluminium treatment, 50% of the rabbits already revealed neurofibrillary degeneration, corresponding to the time-point when desferrioxamine treatment was begun in the above animals; on quantitation, 7.5% of ventral lumbar cord neurons were involved. These findings indicate a partial reversal of aluminium-induced neurodegeneration by desferrioxamine. Delaying desferrioxamine treatment to 6 days after aluminium administration prevented any reversal of the aluminium effect; all animals had abundant neurofibrillary degeneration as well as a striking basophilic spicular deposit of calcium and argyrophilic material in the leptomeninges, lateral ventricles and brain parenchyma adjacent to these areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum neurotoxicity in experimental animals

Neurotoxic effects of aluminum (Al) were recognized > 100 years ago, but have only recently been studied in detail. By far, the most dramatic effect of Al is that of producing intraneuronal perikaryal neurofilamentous aggregates, which consist of phosphorylated neurofilaments. Several species have been used to demonstrate this effect, rabbit being most common; the effect also is seen in in vitro systems. Besides its role in producing neurofibrillary pathology, Al appears to modify the blood-brain barrier and exert cholinergic and noradrenergic effects. Possible mechanisms of Al neurotoxicity could be related to cell damage via free radical production, impairment of glucose metabolism, and effects on signal transduction.

Immunogenicity of wild-type and vaccine strains of Japanese encephalitis virus and the effect of haplotype restriction on murine immune responses

The Chinese live attenuated Japanese encephalitis (JE) virus vaccine clone SA14-14-2 produced in primary hamster kidney (PHK) cells has been adapted to primary dog kidney cells (PDK) for use as a live attenuated human vaccine. In this study we have compared the immunogenicity in mice of SA14-14-2 (PDK) and SA14-14-2 (PHK); also included was the wild-type parent to the vaccine clones, SA14, and another wild-type JE virus strain Nakayama (original). It was found that Balb/c (H-2d) mice given a single dose of 10(3) or 10(6) p.f.u. of live SA14-14-2 (PHK) virus elicited a superior neutralizing (N) antibody response as compared to the same dosages of live SA14-14-2 (PDK) virus. However, if the vaccine clones were inactivated and administered in a two-dose regime the N antibody response elicited was similar for the two viruses. This observation may be explained by differences in the replication efficiency in vivo of the respective vaccine clones. The humoral immune response to all the virus strains in this study elicited by different inbred mouse strains each carrying a discrete haplotype (Balb/c (H-2d), C3H (H-2k), C57BL/6 (H-2b)) were also assessed using haemagglutination inhibition (HAI) and N assays. Viruses were shown to elicit patterns of high and low N-antibody response depending on the major histocompatibility complex (MHC) make-up of the mouse strains. However, the patterns did not necessarily coincide when HAI and N titre reactivity patterns were compared for the same virus strain.

Idiotypic IgM on a B-cell surface requires processing for recognition by anti-idiotypic T cells

Immunization with purified idiotypic IgM derived from the BCL1 lymphoma generates CD4-positive T cells which proliferate specifically in response to idiotypic antigen expressed at the surface of the BCL1 tumor cells. These T cells have been hybridized and two cloned hybridomas have been used to study the molecular nature of the idiotypic antigen recognized. Endogenous presentation of idiotype by the B cells generated IL-2 from the T-cell hybridomas, as measured by a CTLL response. Presentation was inhibited in a dose-dependent manner by chloroquine or ammonium chloride, both of which affect proteolytic degradation of antigen in the endosomes. Similar results were obtained with inhibitors of metabolism or protein synthesis. However, none of these reagents affected expression of idiotypic IgM at the cell surface under the conditions used, indicating that whole IgM is not interacting directly with the T-cell receptor. Interaction between the presenting B cells and T-cell hybridomas was inhibited by anti-CD4 and, in one case, by a monoclonal antibody directed against a determinant in the I-Ed region of the MHC Class II. Inhibition also occurred with antibodies against IgM, either anti-constant region or anti-idiotype, and the univalent Fab' gamma fragment was an effective inhibitor. These data indicate that the B cell constitutively presents its endogenous idiotypic immunoglobulin to CD4-positive T cells following endocytosis from the surface, proteolytic degradation, and interaction with MHC Class II molecules. This endogenous pathway is perturbed by binding of exogenous anti-immunoglobulin antibody, perhaps mimicking what might occur when surface immunoglobulin encounters antigen.

Long-term oral or intravenous aluminum administration in rabbits. I. Renal and hepatic changes

Long-term aluminum (Al) administration was studied in rabbits using intravenous (I.V.) injections of aluminum maltol or oral aluminum citrate in drinking water along with calcium. In the intravenous study, renal and liver tissue Al levels increased and were associated with proximal renal tubular pathology and with hepatic periportal Al-positive multinucleated cells. After oral Al, renal Al levels were increased in the Al-hard water group, while hepatic Al levels were not significantly increased over controls. However, cirrhosis was found in five orally-loaded animals which received Al and/or low dietary calcium or soft water. Collectively, these findings suggest that renal accumulation of Al is causally related to nephrotoxicity; that the lack of renal changes after oral loading is due to low absorption from normal adult gastrointestinal tract and normal functioning of mature kidneys; and that the elevated liver Al levels, achieved after I.V. administration, are related to the presence of hepatic Al-containing giant cells.

Long-term oral aluminum administration in rabbits. II. Brain and other organs

Aluminum (Al) was given orally as a citrate salt in either hard or soft water in combination with low or normal dietary calcium intake over the duration of 12 months using 60 healthy, young adult male New Zealand white rabbits, age four to seven months, divided into six groups. Although decreased weight gain was noted, no significant histological changes were found in the central or peripheral nervous system or in multiple other organs except for liver, nor were tissue levels of Al elevated in brain or liver. However, Al in renal tissue was increased after 52 weeks of treatment in Group 1 (which received Al and a low calcium diet), in spleen in Groups 1 and 2 (on Al and a low calcium diet), and in bone in Group 1. Thus, although the mature intestine acts as a relatively impermeable barrier, some Al is, in fact, absorbed and deposited.

Trace metals: essential nutrients or toxins

Trace metals play important roles in biological processes, both as essential components and toxins. Monitoring body status of trace metals thus has become an important function of many clinical, industrial, and government laboratories. Deficiencies of some essential trace metals are seen occasionally, but of most importance is the area of metal toxicity resulting from environmental, occupational, accidental, or iatrogenic exposure. Major questions persist about which specimen best reflects body status, and in this regard each metal has different requirements. Blood is used most widely, urine has a few applications, and hair can be used, although external contamination is an ever-present problem. Tissue is by far the best specimen but is not easily obtained. Contamination of specimens during collection and processing must be controlled. Of the instrumental techniques available, atomic absorption spectrometry has been used most widely, particularly with electrothermal and atomization approaches.

Identification of envelope protein epitopes that are important in the attenuation process of wild-type yellow fever virus

Monoclonal antibodies (MAbs) have been prepared against vaccine and wild-type strains of yellow fever (YF) virus, and envelope protein epitopes specific for vaccine (MAbs H5 and H6) and wild-type (MAbs S17, S18, S24, and S56) strains of YF virus have been identified. Wild-type YF virus FVV, Dakar 1279, and B4.1 were each given six passages in HeLa cells. FVV and B4.1 were attenuated for newborn mice following passage in HeLa cells, whereas Dakar 1279 was not. Examination of the envelope proteins of the viruses with 87 MAbs showed that attenuated viruses gained only the vaccine epitope recognized by MAb H5 and lost wild-type epitopes recognized by MAbs S17, S18, and S24 whereas the nonattenuated Dakar 1279 HeLa p6 virus did not gain the vaccine epitope, retained the wild-type epitopes, and showed no other physical epitope alterations. MAb neutralization-resistant (MAbr) escape variants generated by using wild-type-specific MAbs S18 and S24 were found to lose the epitopes recognized by MAbs S18 and S24 and to acquire the epitope recognized by vaccine-specific MAb H5. In addition, the MAbr variants became attenuated for mice. Thus, the data presented in this paper indicate that acquisition of vaccine epitopes and loss of wild-type epitopes on the envelope protein are directly involved in the attenuation process of YF virus and suggest that the envelope protein is one of the genes encoding determinants of YF virus pathogenicity.

Variation in the biological function of envelope protein epitopes of yellow fever vaccine viruses detected with monoclonal antibodies

Three different virus strains (17D-204, 17DD and the French neurotropic vaccine) have been used as live attenuated yellow fever (YF) vaccines and are manufactured in different centres around the world. The envelope proteins of these vaccine viruses were examined and compared using mouse monoclonal antibodies (MAbs) in haemagglutination inhibition (HAI) and neutralization (N) tests. The epitopes eliciting HAI and/or N were found to vary depending on the virus examined. Such variation was also found between vaccine viruses of the same strain manufactured in different centres. These data were confirmed by the use of mouse polyclonal antisera. On the basis of the MAb results in HAI tests a dendrogram of the similarity coefficients between the viruses was constructed and showed that the viruses could be placed into three major groups. Thus, it is concluded that YF vaccines manufactured in different centres are antigenically distinct as recognized by the mouse immune system.

Hematological changes after long-term aluminum administration to normal adult rabbits

The effects of long-term aluminum exposure on erythroid parameters were investigated in a rabbit system. Healthy young adult male rabbits were maintained on drinking water containing five mg per L of aluminum citrate; others were treated with an intravenous solution of aluminum maltol, 0.225 mmol of aluminum per week. In the oral study, decreases in the hematocrit, hemoglobin, and red cell count were observed over a 12-month period in those animals on soft water with a low calcium content and containing aluminum citrate; however, no changes were seen in those on hard water containing aluminum citrate nor in rabbits maintained on a normal diet. Small amounts of aluminum were observed in bone marrow macrophages, usually accompanied by iron, in both the orally- and intravenously-treated animals. There was poor correlation between bone marrow aluminum content and length of exposure.

Immunogenicity of experimental live attenuated Japanese encephalitis vaccine viruses and comparison with wild-type strains using monoclonal and polyclonal antibodies

A total of 105 hybridomas secreting anti-Japanese encephalitis (JE) virus monoclonal antibodies (mAbs) were generated from six fusions against four strains of JE virus: wild-type strains SA14 and G8924 and live attenuated vaccines SA14-5-3 and SA14-14-2 (PDK-9). Most of the mAbs (87%) elicited haemagglutination inhibition activity while only a minority (24%) elicited neutralization. None of the mAbs prepared against SA14-5-3, parent of SA14-14-2, elicited neutralization while the only mAbs prepared against SA14-14-2 that elicited neutralization recognized flavivirus cross-reactive epitopes. In comparison, mAbs raised against wild-type strains showed that a spectrum of epitopes with different specificities, including JE type-specific epitopes, elicited neutralizing activity. Two mAbs, prepared against SA14-5-3 virus, were found to be vaccine-specific and five, prepared against strains SA14 and G8924, were wild-type-specific.

Antigenic characterization of the live attenuated Japanese encephalitis vaccine virus SA14-14-2: a comparison with isolates of the virus covering a wide geographic area

In China, a live attenuated Japanese encephalitis (JE) vaccine, based on strain SA14-14-2, has been derived from the wild-type strain SA14 as an alternative to the current inactivated vaccines such as Nakayama-NIH and P-3. SA14-14-2 has been characterized using monoclonal antibodies derived in mice, using HAI and neutralization tests, and compared with other Chinese live vaccine clones and 14 wild-type strains of JE virus. Wild-type strain SA14 was found to be a poor immunogen and antigenically distant from all other viruses examined. The vaccine derivatives SA14-5-3 was more immunogenic than its wild-type parent, while SA14-14-2 (derived from SA14-5-3) was more immunogenic than SA14-5-3 and elicited a cross neutralizing antibody response. Our studies indicated that JE virus strain Nakayama elicited as good a neutralizing antibody response in hyperimmunized mice as the SA14-14-2 vaccine clones grown in either primary hamster kidney (PHK) or primary dog kidney (PDK) cells. A single dose of live SA14-14-2 (PHK) also elicited a good antibody response. Antigenic variation between wild-type and vaccine clones of JE virus were detected but were not considered significant in terms of controlling JE virus infections by vaccination.

In vitro homotypic and heterotypic interference by defective interfering particles of West Nile virus

Defective interfering (DI) particles of the flavivirus West Nile (WN) were generated after as few as two high multiplicity serial passages in Vero and LLC-MK2 cells. Six cell lines (Vero, LLC-MK2, L929, HeLa, BHK-21 and SW13) were used to assay interference by DI particles in a yield reduction assay. Interference was found to vary depending on the cell type used. The highest levels of interference were obtained in LLC-MK2 cells, whereas no detectable effect was observed in BHK-21 and SW13 cells. The ability of DI virus to be propagated varied depending on the cell line used; no detectable propagation of DI virus was observed in SW13 cells. Optimum interference was obtained following co-infection of cells with DI virus and standard virus at a multiplicity of 5. Interference between DI and standard viruses occurred only when they were co-infected or when cells were infected with DI virus 1 h before standard virus. Investigation of heterotypic interference by DI particles of WN virus strains from Sarawak, India and Egypt revealed that interference was dependent on the strain of WN virus or flavivirus used as standard virus. A measure of the similarity between five strains of WN virus and other flaviviruses was made on the basis of interference by DI viruses, and was found to be similar to that based on haemagglutination inhibition tests using a panel of monoclonal antibodies.

Aluminium maltol-induced neurocytoskeletal changes in fetal rabbit midbrain in matrix culture

We have developed a neuronal culture system to evaluate the neurotoxic effects of aluminium maltol on fetal rabbit midbrain sections containing the oculomotor nucleus. Cultures were treated with 5, 7, 9, 11, 13 and 15 mumol/l aluminium maltol or 39 and 45 mumol/l maltol (molal equivalents to 13 and 15 mumol/l aluminium maltol). Control cultures were maintained in nutrient medium alone. Silver-positive neuritic swellings and occasional perikaryal neurofibrillary tangles were observed in cultures treated with 11, 13 and 15 mumol/l aluminium maltol. The number of tangles (involved neurons) produced in aluminium maltol treated cultures were counted and compared to (untreated) controls. We observed a total of 3, 7 and 7% of involved neurons following treatment with 11, 13 and 15 mumol/l aluminium maltol respectively, and none in the control group. By immunohistochemistry, neurofibrillary tangles were immunoreactive with MAbs to phosphorylated (SMI-31), non-phosphorylated, phosphorylation dependent (SMI-32) and phosphorylation independent (SMI-33) epitopes of the high (-H) and middle (-M) molecular weight neurofilament subunits (NF-H/M). By contrast these lesions were nonreactive with MAbs recognizing tau, MAP2 or different beta-tubulin isotypes. The perikaryal tangles consisted of focal accumulations of 10 nm straight filaments by electron microscopy. These findings are in agreement with previous data from rabbit in vivo studies after the administration of aluminium maltol intravenously (Bertholf et al., 1989) or intraventricularly (Katsetos et al., 1990). Using this in vitro system, aluminium-induced neurofibrillary tangles can be consistently produced, and changes in the distribution of neurofilament proteins evaluated. These studies may aid in the assessment of the possible role of aluminium in the aetiology of human neurodegenerative disorders.

Neuronal cytoskeletal lesions induced in the CNS by intraventricular and intravenous aluminium maltol in rabbits

The antigenicity of neuronal cytoskeletal lesions was studied immunohistochemically in adult New Zealand white rabbits after intraventricular (subacute) and intravenous (chronic) administration of a water-soluble aluminium compound, aluminium (Al) maltol. After short-term intraventricular administration, rabbits developed widespread neurofibrillary degeneration (NFD) involving pyramidal neurons of the isocortex and allocortex, projection neurons of the diencephalon, and nerve cells of the brain stem and spinal cord. There was a predilection for motor neuron involvement and for the infratentorial portions of the neuraxis. Perikarya and proximal neurites were especially affected. Bundles of 10 nm filaments were frequently present. Three of the animals treated intravenously for 12 weeks or longer displayed NFD in the oculomotor complex and in the pyramidal neurons of the occipital isocortex. Following either mode of administration, the affected neurons exhibited immunostaining with a panel of monoclonal antibodies (MAbs) against phosphorylated (SMI-31), non-phosphorylated/phosphatase-sensitive (SMI-32), and dephosphorylation-independent (SMI-33) epitopes of high and middle molecular weight neurofilament (NF) protein subunits. They were non-reactive with MAbs to microtubule-associated protein 2 and the class III neuron-associated beta-tubulin isotype. Our findings indicate that intraventricular Al maltol produces similar, but more widespread degeneration of projection-type neurons than the less water-soluble Al compounds as reported by others. The NFD lesions are compared with those of senile dementia of the Alzheimer type (SDAT) and motor neuron disease.

Effect of administration of sodium aurothiomalate on the virulence of yellow fever viruses in adult mice

Administration of sodium aurothiomalate (SATM) to adult mice results in a reduction of their average survival time (AST) following intracerebral challenge with the wild-type strains, Asibi and French viscerotropic virus (FVV), of yellow fever (YF) virus. Most attenuated 17D YF vaccines, derived by passage of the wild-type Asibi strain in chick tissue, showed no reduction in AST following intracerebral challenge and administration of SATM. In contrast, challenge with the majority of live attenuated French neurotropic vaccines, derived by passage of FVV in mouse brain, still resulted in SATM reducing the AST of mice. SATM also changed some YF viruses from non-lethal to lethal following intraperitoneal challenge and negated the ability of a monoclonal antibody to elicit passive protection of mice challenged intracerebrally with YF virus.

Critical appraisal of two methods for determining aluminum in blood samples

We report two methods for determining aluminum concentrations in blood. Method 1, proposed for routine monitoring of patients with chronic renal failure, includes a collection procedure that can be adopted by any renal dialysis unit, with a minimum of sample contamination. Plasma samples are diluted fourfold with HNO3/Triton X-100 matrix modifier. Method 2 is proposed for determining aluminum concentrations in patients with normal renal function, e.g., in drug studies and environmental monitoring. Samples are diluted with an equal volume of Mg(NO3)2 matrix modifier and atomized from a L'vov platform. By either method, analytical recovery of aluminum added to serum ranged between 92% and 105% throughout the linear calibration range. The reference interval (mean +/- SD) for aluminum in 22 healthy subjects by method 2 was 0.044 +/- 0.030 mumol/L.

Critical appraisal of two methods for determining aluminum in blood samples

We report two methods for determining aluminum concentrations in blood. Method 1, proposed for routine monitoring of patients with chronic renal failure, includes a collection procedure that can be adopted by any renal dialysis unit, with a minimum of sample contamination. Plasma samples are diluted fourfold with HNO3/Triton X-100 matrix modifier. Method 2 is proposed for determining aluminum concentrations in patients with normal renal function, e.g., in drug studies and environmental monitoring. Samples are diluted with an equal volume of Mg(NO3)2 matrix modifier and atomized from a L'vov platform. By either method, analytical recovery of aluminum added to serum ranged between 92% and 105% throughout the linear calibration range. The reference interval (mean +/- SD) for aluminum in 22 healthy subjects by method 2 was 0.044 +/- 0.030 mumol/L.

Aspects of aluminum toxicity

Aluminum is the most abundant metal in the earth's crust. The widespread occurrence of aluminum, both in the environment and in foodstuffs, makes it virtually impossible for man to avoid exposure to this metal ion. Attention was first drawn to the potential role of aluminum as a toxic metal over 50 years ago, but was dismissed as a toxic agent as recently as 15 years ago. The accumulation of aluminum, in some patients with chronic renal failure, is associated with the development of toxic phenomena; dialysis encephalopathy, osteomalacic dialysis osteodystrophy, and an anemia. Aluminum accumulation also occurs in patients who are not on dialysis, predominantly infants and children with immature or impaired renal function. Aluminum has also been implicated as a toxic agent in the etiology of Alzheimer's disease, Guamiam amyotrophic lateral sclerosis, and parkinsonism-dementia.

Effects of renal failure

The multiple features of the syndrome of uremia are a result of the retention of a wide variety of metabolic end products. Although a number of metabolites have been incriminated as "the uremic toxin," none of them accounts for all aspects of uremia. It is likely that the uremic syndrome is a result of the pathological effects of many retained substances. Of major current interest is the development of toxicity in brain, bone and other tissues due to accumulation of aluminum. The recognition of aluminum toxicity may have implications not only in patients with impaired renal function but also in other disease states.