Potential neoplastic evolution of Vero cells: in vivo and in vitro characterization

Vero cell lines are extensively employed in viral vaccine manufacturing. Similarly to all established cells, mutations can occur during Vero cells in vitro amplification which can result in adverse features compromising their biological safety. To evaluate the potential neoplastic evolution of these cells, in vitro transformation test, gene expression analysis and karyotyping were compared among low- (127 and 139 passages) and high-passage (passage 194) cell lines, as well as transformed colonies (TCs). In vivo tumorigenicity was also tested to confirm preliminary in vitro data obtained for low passage lines and TCs. Moreover, Vero cells cultivated in foetal bovine serum-free medium and derived from TCs were analysed to investigate the influence of cultivation methods on tumorigenic evolution. Low-passage Vero developed TCs in soft agar, without showing any tumorigenic evolution when inoculated in the animal model. Karyotyping showed a hypo-diploid modal chromosome number and rearrangements with no difference among Vero cell line passages and TCs. These abnormalities were reported also in serum-free cultivated Vero. Gene expression revealed that high-passage Vero cells had several under-expressed and a few over-expressed genes compared to low-passage ones. Gene ontology revealed no significant enrichment of pathways related to oncogenic risk. These findings suggest that in vitro high passage, and not culture conditions, induces Vero transformation correlated to karyotype and gene expression alterations. These data, together with previous investigations reporting tumour induction in high-passage Vero cells, suggest the use of low-passage Vero cells or cell lines other than Vero to increase the safety of vaccine manufacturing.     

Recent clinical isolates of cytomegalovirus suppress human cytomegalovirus-specific human leukocyte antigen-restricted cytotoxic T-lymphocyte activity.

Peripheral blood mononuclear cells harvested from healthy adults seropositive for human cytomegalovirus (HCMV) and cultured with laboratory strain AD-169 demonstrated human leukocyte antigen-restricted and HCMV-specific killing on target cells infected with either HCMV laboratory strain AD-169 or recent low-passage HCMV isolates. These results indicated that the determinants recognized by cytotoxic T lymphocytes (CTLs) are shared among different strains of HCMV. However, when low-passage isolates, rather than high-passage AD-169 virions, were used to stimulate CTL activity, the lytic response was significantly lower against all targets. Mixing of AD-169 and low-passage HCMV isolates induced low CTL activity. Collectively, the findings suggest that low-passage HCMV isolates have dual effects--antigenic stimulation and immunosuppression--whereas laboratory strain AD-169 is primarily immunogenic. The study of several recent isolates indicated that they varied in their ratio of immunostimulation to suppression, that infectious virus was necessary to produce suppression, and that suppressive isolates did not have to be present at the initiation of culture to exert their suppressive effects.     

Serum neutralization of feline immunodeficiency virus is markedly dependent on passage history of the virus and host system.

Sera from feline immunodeficiency virus (FIV)-infected cats exhibited extremely low levels of neutralizing antibodies against virus passaged a few times in vitro (low passage), when residual infectivity was assayed in the CD3+ CD4- CD8- MBM lymphoid cell line or mitogen-activated peripheral blood mononuclear cells. By sharp contrast, elevated titers of highly efficient neutralizing activity against FIV were measured, by use of high-passage virus, in assays on either the fibroblastoid CrFK or MBM cell line. However, high-passage virus behaved the same as low-passage virus after one in vivo passage in a specific-pathogen-free cat and reisolation. Subneutralizing concentrations of infected cat sera enhanced the production of low-passage virus by MBM cells, an effect not seen with high-passage virus in CrFK cells. These qualitative and quantitative discrepancies could not be attributed to differences in the amount of immunoreactive viral material, to the amount of infectious virus present in the viral stocks, or to the presence of anti-cell antibodies. The observed effects were most likely due to the different passage history of the viral preparations used. The observation that neutralizing antibodies detected with high-passage virus were broadly cross-reactive in assays with CrFK cells but isolate specific in MBM cells suggests also that the cell substrate can influence the result of FIV neutralization assays. This possibility could not be tested directly because FIV adapted to grow in CrFK cells had little infectivity for lymphoid cells and vice versa. In vitro exposure to infected cat sera had little or no effect on the ability of in vivo-passaged FIV to infect cats. These data reveal no obvious relationship between titers against high-passage virus and ability to block infectivity of FIV in cats and suggest caution in the use of such assays to measure vaccine efficacy. In conclusion, by contrast with what has been previously reported for the use of CrFK cells and high-passage virus, both natural and experimental infections of cats with FIV generate poor neutralizing antibody responses with regard to in vivo protection.     

人类巨细胞病毒UL133基因在临床低传代株中的多态性研究

人类巨细胞病毒在多次传代后,会表现出不同的毒力水平.与临床低传代株Toledo相比,实验室高传代株AD169缺失了19个开放阅读框(ORF).这19个基因被认为是与HCMV致病性最可能相关的一组基因,研究这些基因的多态性对揭示HCMV致病性的遗传基础具有指导意义.UL133基因是这19个ORF中的一个.以临床低传代株Toledo和Merlin为对照,分析了23个临床病毒株UL133基因的遗传多态性.序列分析表明,UL133基因具有一定的多态性,Toledo株、Merlin株与我们分离到的临床株一起可分为3个基因型:G1、G2和G3.G2、G3型毒株均能导致先天性感染.没有发现UL133基因型与患儿临床疾病的必然关联.     

Analysis of Borrelia burgdorferi membrane architecture by freeze-fracture electron microscopy.

Freeze-fracture electron microscopy was used to investigate the membrane architectures of high-passage Borrelia burgdorferi B31 and low- and high-passage isolates of B. burgdorferi N40. In all three organisms, fractures occurred almost exclusively through the outer membrane (OM), and the large majority of intramembranous particles were distributed randomly throughout the concave OM leaflet. The density of intramembranous particles in the concave OM leaflet of the high-passage N40 isolate was significantly greater than that in the corresponding leaflet of the low-passage N40 isolate. Also noted in the OMs of all three organisms were unusual structures, designated linear bodies, which typically were more or less perpendicular to the axis of the bacterium. A comparison of freeze-fractured B. burgdorferi and Treponema pallidum, the syphilis spirochete, revealed that the OM architectures of these two pathogens differed markedly. All large membrane blebs appeared to be bounded by a membrane identical to the OM of B. burgdorferi whole cells; in some blebs, the fracture plane also revealed a second bilayer closely resembling the B. burgdorferi cytoplasmic membrane. Aggregation of the lipoprotein immunogens outer surface protein A (OspA) and OspB on the bacterial surface by incubation of B. burgdorferi B31 with specific polyclonal antisera did not affect the distribution of OM particles, supporting the contention that lipoproteins do not form particles in freeze-fractured OMs. The expression of poorly immunogenic, surface-exposed proteins as virulence determinants may be part of the parasitic strategy used by B. burgdorferi to establish and maintain chronic infection in Lyme disease.     

Emergence of distinct genetic variants in the population of primary Bartonella henselae isolates

Bartonella henselae isolates from different hosts display a marked genetic heterogeneity, as determined by pulsed-field gel electrophoresis (PFGE). The aim of the present study was to determine whether different genetic variants may coexist within the population of distinct B. henselae isolates and could be detected by PFGE. Three primary B. henselae isolates and the B. henselae reference strains ATCC 49793 and 49882 were subjected as single colony derived cultures in quadruplicate to PFGE analysis upon restriction with SmaI or NotI. Up to 4 fragment differences were found among the cultures obtained from each primary isolate, indicating the coexistence of genetic variants in the population of primary B. henselae isolates. The clonal relatedness of the genetic variants was confirmed by arbitrarily primed PCR and multi-locus sequence typing. In contrast to the primary isolates, no variants were detected among the single colony derived cultures of the high-passage ATCC strains. We hypothesized that the coexistence of different genetic variants may represent a feature that is restricted to primary or low-passage B. henselae isolates. The primary isolates were serially passed in vitro and then subjected as single colony derived cultures to PFGE analysis, which now revealed identical patterns among the quadruplicate cultures of each high-passage isolate. These results suggest that the population of a primary B. henselae isolate is composed of distinct genetic variants, which may disappear upon repeated passages on artificial culture media. Generation of genetic variants by B. henselae may represent an escape mechanism to circumvent the host specific immune responses.     

Pathogenicity for several laboratory animals of toxoplasma oocysts originated from naturally infected cats.

The pathogenicity of four strains, O-1, O-2, O-3, and O-4, of Toxoplasma isolated in the form of oocyst from the feces of naturally infected cats was examined for such laboratory animals as mice, rats, rabbits, guinea pigs, and dogs, in comparison with that of the Beverley strain. Suspensions of seven graded doses of oocysts of each strain ranging from 1.0 X 10(-1) to 1.0 X 10(5) were inoculated orally into seven groups of five mice each. The O-1, O-2, and O-3 strains were as pathogenic for mice as the Beverley strain, but the O-4 strain was not so pathogenic as any other strain. Rats, rabbits, guinea pigs, and dogs were inoculated orally with around 1.0 X 10(5) oocysts. The four O strains were not so severly pathogenic for rats and rabbits as to cause death. The O-2 and O-3 strains showed strong pathogenicity for guinea pigs, almost all of which, when inoculated with them, died after manifesting severe clinical symptoms. The pathogenicity of the O-1 and O-2 strains showed essentially the same tendency for dogs as for any other animal. In inoculation with oocysts, as well as with proliferative forms or cysts, the same pathogenicity was not observed in different strains, even if the same species of host animals was used. On the contrary, the same pathogenicity was not always found even in one strain when a different species of animals was used.     

Variation in Galr1 expression determines susceptibility to exocitotoxin-induced cell death in mice

Inbred strains of mice differ in their susceptibility to excitotoxin-induced cell death, but the genetic basis of individual variation in differential susceptibility is unknown. Previously, we identified a highly significant quantitative trait locus (QTL) on chromosome 18 that influenced susceptibility to kainic acid-induced cell death ( Sicd1 ). Comparison of susceptibility to seizure-induced cell death between reciprocal congenic lines for Sicd1 and parental background mice indicates that genes influencing this trait were captured in both strains. Two positional gene candidates, Galr1 and Mbp , map to 55 cM, where the Sicd1 QTL had been previously mapped. Thus, this study was undertaken to determine if Galr1 and/or Mbp could be considered as candidate genes. Genomic sequence comparison of these two functional candidate genes from the C57BL/6J (resistant at Sicd1 ) and the FVB/NJ (susceptible at Sicd1 ) strains showed no single-nucleotide polymorphisms. However, expression studies confirmed that Galr1 shows significant differential expression in the congenic and parental inbred strains. Galr1 expression was downregulated in the hippocampus of C57BL/6J mice and FVB.B6- Sicd1 congenic mice when compared with FVB/NJ or B6.FVB- Sicd1 congenic mice. A survey of Galr1 expression among other inbred strains showed a significant effect such that 'susceptible' strains showed a reduction in Galr1 expression as compared with 'resistant' strains. In contrast, no differences in Mbp expression were observed. In summary, these results suggest that differential expression of Galr1 may contribute to the differences in susceptibility to seizure-induced cell death between cell death-resistant and cell death-susceptible strains.     

Infectivity of preserved Cryptosporidium parvum oocysts for immunosuppressed adult mice

Abstract The present study was undertaken to determine the infectivity of Cryptosporidium parvum oocysts for immunosup-pressed adult C57BL/6N mice after the oocysts had been stored from 1–48 months at 4°C in 2.5% potassium dichromate. All mice inoculated with oocysts 1–18 months old developed patent infections, while mice inoculated with older oocysts remained uninfected. The prepatent period was extended from 2 to 6 or 7 days as the storage time for oocysts increased. The finding that C. parvum oocysts remain infective for mice for at least 18 months offers important economic and time-saving advantages for investigators who frequently require large numbers of oocysts that must be painstakingly purified from calf manure.     

Immunogenicity of wild and attenuated varicella-zoster virus strains in pygmy marmosets

Pygmy marmosets were inoculated with the low-passage parental strain or with the attenuated variant of OKA strain of varicella-zoster virus. No clinical signs were observed following inoculation and virus could not be isolated from tissues taken at several times after inoculation. A low-level antibody response developed in all animals. Three months after the first inoculation, all animals were challenged with the low-passage parental strain of virus. Animals primed originally with the parental strain developed higher booster responses than animals primed with the attenuated strain of virus. The results suggest that the parental and attenuated strains of varicella-zoster virus differ in their immunogenicity in pygmy marmosets.     

Evolution of the Borrelia burgdorferi outer surface protein OspC.

The genes coding for outer surface protein OspC from 22 Borrelia burgdorferi strains isolated from patients with Lyme borreliosis were cloned and sequenced. For reference purposes, the 16S rRNA genes from 17 of these strains were sequenced after being cloned. The deduced OspC amino acid sequences were aligned with 12 published OspC sequences and revealed the presence of 48 conserved amino acids. On the basis of the alignment, OspC could be divided into an amino-terminal relatively conserved region and a relatively variable region in the central portion. The distance tree obtained divided the ospC sequences into three groups. The first group contained ospC alleles from all (n = 13) sensu stricto strains, the second group contained ospC alleles from seven Borrelia afzelii strains, and the third group contained ospC alleles from five B. afzelii and all (n = 9) Borrelia garinii strains. The ratio of the mean number of synonymous (dS) and nonsynonymous (dN) nucleotide substitutions per site calculated for B. burgdorferi sensu stricto, B. garinii, and B. afzelii ospC alleles suggested that the polymorphism of OspC is due to positive selection favoring diversity at the amino acid level in the relatively variable region. On the basis of the comparison of 16S rRNA gene sequences, Borrelia hermsii is more closely related to B. afzelii than to B. burgdorferi sensu stricto and B. garinii. In contrast, the phylogenetic tree obtained for the B. hermsii variable major protein, Vmp33, and 18 OspC amino acid sequences suggested that Vmp33 and OspC from B. burgdorferi sensu stricto strains share a common evolutionary origin.     

Characterization of temperature-sensitive strains of Neospora caninum in mice

Temperature-sensitive (ts) strains of the Neospora caninum tachyzoites were selected by chemical mutagenesis and selection for growth at 32 C. Three ts strains and the parental, N. caninum wild-type strain, NC-1, were examined in the present study for their ability to cause disease in inbred BALB/c mice, outbred ICR mice, and chemically immunosuppressed ICR mice. In BALB/c mice, all 3 strains failed to induce clinical disease, whereas infection with the NC-1 strain caused central nervous system disease and death in some mice. No disease was observed in ICR mice inoculated with the 3 ts strains or the NC-1 strain. All immunosuppressed ICR mice inoculated with the NC-1 strain died, whereas no immunosuppressed mice inoculated with the NCts-4 strain and only 1 of 5 mice inoculated with the NCts-8 and NCts-12 strains died. The NCts-4 and NCts-12 strains reverted to a wild-type phenotype when grown at 37 C. Vaccination of BALB/c mice with live, but not frozen NCts-8 strain tachyzoites induced significant (P < 0.05) protection following NC-1 strain challenge.     

Regulation of alpha-fetoprotein and transferrin synthesis and secretion in mouse hepatoma cells

Significant differences in the glucocorticoid- and cyclic nucleotide-mediated regulation of the secretory glycoproteins, α-fetoprotein and transferrin, have been observed to develop in a mouse hepatoma cell line, Hepa-2, after many passages in culture. Treatment of low-passage cells with hydrocortisone (10^?6m), N⁶,O²-dibutyryl cyclic AMP (10^?3m), or 8-bromo-cyclic AMP (10^?3m) results in 1.5-, 2- to 4-, and 5.5- to 6-fold increases, respectively, in the rates of synthesis and secretion of α-fetoprotein. As expected of secretory proteins, the ratio of synthesis to secretion is 1 and remains unaltered when treatment with hydrocoritsone, N⁶,O²-dibutyryl cyclic AMP, and 8-bromo-cyclic AMP causes a stimulation of synthesis and secretion. Similar studies showing that albumin and transferrin synthesis and secretion are also balanced in these low-passage cells have been published and indicate that the regulation of synthesis and secretion remains coupled in these low-passage cells. In high-passage Hepa-2 cells, however, we have shown that the relative rate of α-fetoprotein synthesis is higher than its rate of secretion and that the ratio of synthesis to secretion is 4. Similarly, the ratio of transferrin synthesis to secretion is 3.6, whereas it remains unaltered for albumin. When the high-passage cells are treated with N⁶,O²-dibutyryl cyclic AMP, there is a greater increase in the rate of secretion for both glycoproteins, resulting in a reduction of the ratio of synthesis to secretion from 4 to 1.63 for α-fetoprotein and from 3.6 to 2.3 for transferrin. This effect on the secretion of α-fetoprotein and transferrin is specific for the cyclic nucleotides and occurs only in high-passage cells. Hydrocortisone treatment causes an increase in α-fetoprotein synthesis and secretion. However, the ratio of synthesis to secretion increases from 3.96 in control to 5.5 in treated cells. Our studies show, therefore, that there is an increase in this ratio because of a slightly greater effect on synthesis which is not reflected in secretion. Similarly, hydrocortisone exerts a greater increase in transferrin synthesis than secretion and causes the ratio of synthesis to secretion to increase from 3.6 to 6.2. We propose that during continued subculturing a Hepa-2 variant is selected in which the regulation of serum glycoprotein synthesis and secretion is uncoupled. Furthermore, this effect is specific for secretory glycoproteins since the regulation of albumin synthesis and secretion by hydrocortisone and cyclic nucleotides remained unaltered.     

Sodium Valproate Facilitates the Propagation of Granulocytic Ehrlichiae (Anaplasma phagocytophilum) in HL-60 Cells

As already shown, some inducers of the differentiation of promyelocytic cells along the granulocytic pathway, such as dimethylsulphoxide (DMSO) or all-trans retinoic acid, can enhance propagation of granulocytic ehrlichiae in HL-60 cell cultures. This study was conducted to prove whether sodium valproate, a salt of di-n-propylacetic acid (VPA) known to trigger cellular differentiation in several solid and hematopoietic malignancies is similarly efficient in ehrlichial cultures. Two cell lines derived from HL-60, that is, low-passage undifferentiated HL-60 (HL-60F) and high-passage HL-60 spontaneously differentiated towards monocytic phenotype (HL-60J) were grown in RPMI 1640 medium supplemented with 10% FBS. The respective HL-60F and HL-60J IC₅₀-values for NaVPA were estimated to be 0.8 and 2.2 mM under these culture conditions; to stimulate the differentiation, the respective doses of 0.3 and 1.2 mM were then applied. When the NaVPA-treated cells of both lines were challenged with an ehrlichial laboratory strain (HGE), maintained in splenectomized NMRI mice, the respective 1–2 and ≤0.1% primary infection rates in HL-60F and HL-60J cultures were observed 3 days post-inoculation. In comparison, only rare (≤0.1%) infected HL-60F and no infected HL-60J cells were recorded under the same experimental conditions in untreated control cultures. HGE continuously propagated in NaVPA-supplemented HL-60F cultures remained infectious to mice at least up to the 95th passage (12 months). NaVPA can thus facilitated continuous propagation of granulocytic ehrlichiae in cell cultures without a substantial loss of infectiveness. This revised version was published online in July 2006 with corrections to the Cover Date.     

VlsE,the nexus for antigenic variation of the Lyme disease spirochete,also mediates early bacterial attachment to the host microvasculature under shear force

Hematogenous dissemination is a critical step in the evolution of local infection to systemic disease. The Lyme disease (LD) spirochete, which efficiently disseminates to multiple tissues, has provided a model for this process, in particular for the key early event of pathogen adhesion to the host vasculature. This occurs under shear force mediated by interactions between bacterial adhesins and mammalian cell-surface proteins or extracellular matrix (ECM). Using real-time intravital imaging of the Lyme spirochete in living mice, we previously identified BBK32 as the first LD spirochetal adhesin demonstrated to mediate early vascular adhesion in a living mouse; however, deletion of bbk32 resulted in loss of only about half of the early interactions, suggesting the existence of at least one other adhesin (adhesin-X) that promotes early vascular interactions. VlsE, a surface lipoprotein, was identified long ago by its capacity to undergo rapid antigenic variation, is upregulated in the mammalian host and required for persistent infection in immunocompetent mice. In immunodeficient mice, VlsE shares functional overlap with OspC, a multi-functional protein that displays dermatan sulfate-binding activity and is required for joint invasion and colonization. In this research, using biochemical and genetic approaches as well as intravital imaging, we have identified VlsE as adhesin-X; it is a dermatan sulfate (DS) adhesin that efficiently promotes transient adhesion to the microvasculature under shear force via its DS binding pocket. Intravenous inoculation of mice with a low-passage infectious B. burgdorferi strain lacking both bbk32 and vlsE almost completely eliminated transient microvascular interactions. Comparative analysis of binding parameters of VlsE, BBK32 and OspC provides a possible explanation why these three DS adhesins display different functionality in terms of their ability to promote early microvascular interactions.     

A DNA vaccine encoding the outer surface protein C from Borrelia burgdorferi is able to induce protective immune responses

The outer surface protein C (OspC) of Borrelia burgdorferi, the spirochete that causes Lyme disease, is a promising candidate for a vaccine against borreliosis. BALB/c and C3H/HeJ mice were immunized either with recombinant OspC protein or with plasmid DNA encoding OspC fused to the human tissue plasminogen activator leader sequence (pCMV-TPA/ZS7). The influence of the route of administering the DNA and the use of oligodeoxynucleotides containing CpG-motifs on the development of the immune response was investigated. In both mouse strains, protein as well as gene-gun immunization induced Th2 type responses, whereas needle injection of plasmid DNA resulted in Th1 type antibody production. Co-injection of CpG-motifs did not significantly modify the response type in any immunization group, as indicated by only marginal changes of antibody subclass distribution. The protection rate after challenge with 10(4) B. burgdorferi organisms per mouse was between 80% and 100% for all groups. These results demonstrate, for the first time, that a DNA vaccine encoding OspC of B. burgdorferi is suitable for inducing protection against Lyme borreliosis.     

Essential protective role attributed to the surface lipoproteins of Borrelia burgdorferi against innate defences

To initiate infection, a microbial pathogen must be able to evade innate immunity. Here we show that the Lyme disease spirochete Borrelia burgdorferi depends on its surface lipoproteins for protection against innate defences. The deficiency for OspC, an abundantly expressed surface lipoprotein during early infection, led to quick clearance of B. burgdorferi after inoculation into the skin of SCID mice. Increasing expression of any of the four randomly chosen surface lipoproteins, OspA, OspE, VlsE or DbpA, fully protected the ospC mutant from elimination from the skin tissue of SCID mice; moreover, increased OspA, OspE or VlsE expression allowed the mutant to cause disseminated infection and restored the ability to effectively colonize both joint and skin tissues, albeit the dissemination process was much slower than that of the mutant restored with OspC expression. When the ospC mutant was modified to express OspA under control of the ospC regulatory elements, it registered only a slight increase in the 50% infectious dose than the control in SCID mice but a dramatic increase in immunocompetent mice. Taken together, the study demonstrated that the surface lipoproteins provide B. burgdorferi with an essential protective function against host innate elimination.     

Induced defence responses limit Hartig net formation in ectomycorrhizal birch roots

Roots of clonal birches ( Betula pendula ) were inoculated with the ectomycorrhizal fungi Paxillus involutus (isolates P0 and Mi) and Hebeloma cylindrosporum (strains D1 and D105). These fungi showed different rates of mycorrhiza formation in vitro . Mature mycorrhizas were obtained after only 2–4 d with H. cylindrosporum , whereas 6–8 d were necessary with P. involutus isolate P0, and P. involutus isolate Mi was not able to form mature mycorrhiza during the 10 d of the experiment. Temporal changes in PAL activity and the expression of genes encoding intracellular pathogenesis-related proteins were followed after inoculating birch roots with these fungi. Transient increase of PAL activity, and transient induction of expression of the wound-inducible Bet v1-SC1 gene, were observed in roots challenged with both H. cylindrosporum strains and the P. involutus isolate P0. These changes were found to coincide with hyphal penetration between root cells during Hartig net formation, and were never observed in roots inoculated with the poorly aggressive P. involutus isolate Mi. Examination of mycorrhizal root sections under u.v. light indicated the presence of phenolic compounds in the host cell walls at the vicinity of the Hartig net. These results strongly suggest that hyphal penetration between the root cells triggers a transient defence response which, in turn, could limit Hartig net formation to the outer layer of the root cortex.