Cell-culture system for continuous production of Toxoplasma gondii tachyzoites

Evaluation of the protective immune response of an attenuated strain of Toxoplasma gondii with long-term passages on the Gecko cell line

Toxoplasma gondii is an obligate intracellular parasite that causes the zoonoses disease, named toxoplasmosis, with global prevalence. Until now, no cost-effective treatment method has been found to deal with toxoplasma, and vaccination is the best way to deal with the infection. In the case of pathogenic protozoa, mainly live vaccines have had successful results compared to other vaccine platforms. This study evaluated the efficacy of a live experimental vaccine through long-term passages on the Gecko cell line (Z1) in inducing a protective immune response in BALB/c mice. Thirty mice were divided into three equal groups; G1: the immunized/challenged group (injection of attenuated strain), G2: the immunized/unchallenged group (injection of attenuated strain), and G3: the control group (injection of culture medium).One month after immunization, the studied mice were challenged with 1ₓ103 live tachyzoites of Toxoplasma acute RH strain. We performed Serological investigations, including evaluating antibodies, interferon-gamma (IFN-γ), and interleukins 2, 4, 10, and 12 (IL-2,4,10,12). At the study's end, a molecular test was performed on brain and liver tissues in the immunized groups to check the presence of parasites. The results from the serological tests for the evaluation of antibodies, interferon-gamma (IFN-γ), and interleukins 10 and 12 (IL-10, 12) show a significant difference (p < 0.05) between the vaccinated group and the control group, which are essential indicators of protective immunity against toxoplasma infection. Thus, in the vaccinated group, the survival rate of mice against the challenge was 70%. Also, in group two (G2), the attenuated strain of Toxoplasma gondii had no pathogenicity, and all mice survived until the end of the study period. Molecular results also showed the absence of parasites in the brain and liver tissues in this immunized group and the parasite was found in only one case of liver tissue in G1. Therefore, the attenuated strain has caused significant and protective humoral and cellular immune responses in vaccinated groups. This study showed that with the long-term passage of the acute strain on the Gecko cell line, it is possible to quickly obtain a non-diseased attenuated strain with the ability to induce protective immunity. This successful finding can introduce further research to achieve a promising vaccine in the target animals.

Parallel Propagation of Toxoplasma gondii In Vivo, In Vitro and in Alternate Model: Towards Less Dependence on the Mice Model

Toxoplasma gondii is an obligate intracellular protozoan. In pregnant women, it can lead to severe birth defects or intrauterine death of the fetus. Most of what is currently know on cell biology of T. gondii comes from studies relying on the RH strain propagated in mice. According to the recommendations concerning the animal welfare, we assayed in vitro/in vivo procedures to replace, or at least reduce, the demanding animal model for strain propagation. We evaluated the genetic and phenotypic stability of the RH strain throughout its parallel continuous propagation in mice, in human foreskin fibroblasts (HFF) and in an alternate fashion of these two procedures. We also assessed the virulence impact on the RH strain after different periods of its long-term propagation strictly in cells. The RH strain completely lost its virulence after long-term passage in HFF. Nevertheless, we obtained a successful outcome with the alternate passaging of the parasite in HFF and in mice as this approach enabled T. gondii to maintain the evaluated phenotypic properties, mainly its virulence potential. Also, no genetic changes were observed in genes known to be highly polymorphic or involved in pathoadaptation. In conclusion, the alternate model seems to be a feasible method for T. gondii propagation and maintenance, strongly impacting the number of sacrificed mice.

CRISPR/Cas9-Based Knockout of GNAQ Reveals Differences in Host Cell Signaling Necessary for Egress of Apicomplexan Parasites

The coordinated release of apicomplexan parasites from infected host cells prior to reinvasion is a critical process for parasite survival and the spread of infection. While Toxoplasma tachyzoites and Plasmodium blood stages induce a fast disruption of their surrounding membranes during their egress from host cells, Plasmodium liver stages keep the host cell membrane intact and leave their host cell in host cell-derived vesicles called merosomes.

Toxoplasma gondii and members of the genus Plasmodium are obligate intracellular parasites that leave their infected host cell upon a tightly controlled process of egress. Intracellular replication of the parasites occurs within a parasitophorous vacuole, and its membrane as well as the host plasma membrane need to be disrupted during egress, leading to host cell lysis. While several parasite-derived factors governing egress have been identified, much less is known about host cell factors involved in this process. Previously, RNA interference (RNAi)-based knockdown and antibody-mediated depletion identified a host signaling cascade dependent on guanine nucleotide-binding protein subunit alpha q (GNAQ) to be required for the egress of Toxoplasma tachyzoites and Plasmodium blood stage merozoites. Here, we used CRISPR/Cas9 technology to generate HeLa cells deficient in GNAQ and tested their capacity to support the egress of T. gondii tachyzoites and Plasmodium berghei liver stage parasites. While we were able to confirm the importance of GNAQ for the egress of T. gondii, we found that the egress of P. berghei liver stages was unaffected in the absence of GNAQ. These results may reflect differences between the lytic egress process in apicomplexans and the formation of host cell-derived vesicles termed merosomes by P. berghei liver stages.

IMPORTANCE The coordinated release of apicomplexan parasites from infected host cells prior to reinvasion is a critical process for parasite survival and the spread of infection. While Toxoplasma tachyzoites and Plasmodium blood stages induce a fast disruption of their surrounding membranes during their egress from host cells, Plasmodium liver stages keep the host cell membrane intact and leave their host cell in host cell-derived vesicles called merosomes. The knockout of GNAQ, a protein involved in G-protein-coupled receptor signaling, demonstrates the importance of this host factor for the lytic egress of T. gondii tachyzoites. Contrastingly, the egress of P. berghei is independent of GNAQ at the liver stage, indicating the existence of a mechanistically distinct strategy to exit the host cell.

The use of Toxoplasma gondii tachyzoites produced in HeLa cells adhered to Cytodex 1 microcarriers as antigen in serological assays: an application of microcarrier technology

Toxoplasma gondii can infect nearly all warm-blooded animals, including humans. In the laboratory diagnosis of toxoplasmosis, serological tests have importance in detecting antibody response. Traditionally T. gondii tachyzoites grown in vivo are being used as an antigen source in serological assays. Currently, tachyzoites produced in vitro are being tested as an antigen source in order to decrease animal use. Microcarrier technology allowed us to grow anchorage-dependent host cells on microcarrier suspension in short time and approximately 10 times more than traditional flask technique. The ability of T. gondii tachyzoites to grow in host cells adhered to microcarriers has not been analyzed yet. In this study, we aimed to develop a novel in vitro culture method to produce T. gondii tachyzoites abundantly using HeLa cells adhered to Cytodex 1 microcarriers. Initially, the growth of HeLa cells adhered to Cytodex 1 was analyzed using RPMI 1640, DMEM, and EMEM. Next, HeLa cells with a concentration of 1 × 10⁵ cells/ml and 2 × 10⁵cells/ml were adhered to Cytodex 1 and grown in spinner flasks. Then, T. gondii tachyzoites were inoculated with 1:1 and 2:1 cell:tachyzoite ratios to HeLa cells adhered to microcarriers in spinner flaks. During continuous production in spinner flasks, tachyzoites were harvested at the 2nd, 4th, and 7th day of culture and the quality of antigens produced from these tachyzoites were tested in ELISA and Western Blotting using sera of patients with toxoplasmosis. The optimization studies showed that finest HeLa inoculation value was 2 × 10⁵cells/ml using RPMI 1640, and the cell:tachyzoite ratio to obtain the highest tachyzoite yield (17.1 × 10⁷) was 1:1 at the 4th day of inoculation. According to the results of ELISA comparing HeLa cell and mouse derived antigens, the highest correlation with mouse antigen was achieved at the 4th day of HeLa cell culture with 1:1 HeLa:tachyzoite ratio (P < 0.0001). The sensitivity and specificity ratios of ELISA were 100%. In addition, Western blotting banding patterns of the antigen derived at the 4th day of HeLa cell culture with 1:1 HeLa:tachyzoite ratio was comparable with mouse derived antigen. Overall, this novel methodology can be an alternative source of antigen in diagnostic assays, decrease animal use for antigen production, and contribute to the solution of ethical and economic problems.

Virulência e multiplicação de isolados de Toxoplasma gondii da região central do Rio Grande do Sul

RESUMO: O protozoário Toxoplasma gondii possui a capacidade de infectar diversas espécies animais, geralmente causando distúrbios reprodutivos. Quatro diferentes isolados de T. gondii - Pains #1 (P1), Pains #2 (P2), Santa Flora #1 (SF1) e Santa Flora #306 (SF306) - foram avaliados, após prévia genotipagem. A capacidade de multiplicação e virulência destes isolados foi analisada in vitro (células Vero) e in vivo (camundongos), sendo realizadas 3 passagens para cada isolado em cada modo avaliado, sendo sempre inoculada a dose de 1x104 taquizoítos em todas as passagens. Os camundongos eram observados diariamente, quanto à presença de sinais clínicos e ocorrência de mortalidade após inoculação dos taquizoítos. Os isolados SF1 e SF306, foram os que apresentaram maior multiplicação média do número total de taquizoítos em cada uma das 3 diferentes passagens realizadas para cada um dos isolados tanto in vitro quanto in vivo. Os primeiros sinais clínicos observados nos camundongos ocorreram entre os dias 5 a 11, após inoculação, com mortalidade acontecendo entre os dias 6 a 15, após inoculação. Assim, a multiplicação parasitária in vitro é semelhante à multiplicação in vivo destes isolados de T. gondii; diferentes isolados com o mesmo genótipo apresentam comportamento de virulência semelhante, caracterizando o isolado SF1 como mais virulento para camundongos.

Toxoplasma gondii: Laboratory Maintenance and Growth

Toxoplasma gondii is a highly successful apicomplexan protozoan capable of infecting any warm-blooded animal worldwide. In humans, Toxoplasma infections are life-long, with approximately one-third of the world's population chronically infected. Although normally controlled by the host immune system, T. gondii infection can lead to a variety of clinical outcomes in individuals with immature or suppressed immune systems. After penetrating the intestine, parasites rapidly disseminate throughout the body and stimulate production of the cytokines interleukin (IL)-12, IL-18, and interferon (IFN)-γ by immune cells. These cytokines play a key role in host resistance to T. gondii by promoting a strong Th1 response. Recent reports show that gut commensal bacteria can act as molecular adjuvants during T. gondii infection. Thus, T. gondii is an excellent model system to study host-pathogen interactions. This unit outlines the protocols for in vitro and in vivo maintenance and growth of T. gondii. © 2017 by John Wiley & Sons, Inc.

Toxoplasma gondii: One Organism, Multiple Models

Toxoplasma gondii is an intensely studied protozoan parasite. It is also used as a model organism to research additional clinically relevant human and veterinary parasites due to ease of in vitro culture and genetic manipulation. Recently, it has been developed as a model of inflammatory bowel disease, due to their similar pathologies. However, researchers vary widely in how they use T. gondii, which makes study comparisons and interpretation difficult. The aim of this review is to provide researchers with a tool to: (i) determine the appropriateness of the different T. gondii models to their research, (ii) interpret results from the wide range of study conditions, and (iii) consider new advances in technology which could improve or refine their experimental setup.

Induction of interferon-stimulated genes by IRF3 promotes replication of Toxoplasma gondii

Innate immunity is the first line of defense against microbial insult. The transcription factor, IRF3, is needed by mammalian cells to mount innate immune responses against many microbes, especially viruses. IRF3 remains inactive in the cytoplasm of uninfected cells; upon virus infection, it gets phosphorylated and then translocates to the nucleus, where it binds to the promoters of antiviral genes and induces their expression. Such genes include type I interferons (IFNs) as well as Interferon Stimulated Genes (ISGs). IRF3-/- cells support enhanced replication of many viruses and therefore, the corresponding mice are highly susceptible to viral pathogenesis. Here, we provide evidence for an unexpected pro-microbial role of IRF3: the replication of the protozoan parasite, Toxoplasma gondii, was significantly impaired in IRF3-/- cells. In exploring whether the transcriptional activity of IRF3 was important for its pro-parasitic function, we found that ISGs induced by parasite-activated IRF3 were indeed essential, whereas type I interferons were not important. To delineate the signaling pathway that activates IRF3 in response to parasite infection, we used genetically modified human and mouse cells. The pro-parasitic signaling pathway, which we termed PISA (Parasite-IRF3 Signaling Activation), activated IRF3 without any involvement of the Toll-like receptor or RIG-I-like receptor pathways, thereby ruling out a role of parasite-derived RNA species in activating PISA. Instead, PISA needed the presence of cGAS, STING, TBK1 and IRF3, indicating the necessity of DNA-triggered signaling. To evaluate the physiological significance of our in vitro findings, IRF3-/- mice were challenged with parasite infection and their morbidity and mortality were measured. Unlike WT mice, the IRF3-/- mice did not support replication of the parasite and were resistant to pathogenesis caused by it. Our results revealed a new paradigm in which the antiviral host factor, IRF3, plays a cell-intrinsic pro-parasitic role.

Comparison of use of Vero cell line and suspension culture of murine macrophage to attenuation of virulence of Neospora caninum

In this study the tachyzoite yields of Neospora caninum were compared in two cell lines: Vero (African Green Monkey Kidney) and suspension culture of murine macrophage (J774) cell lines. Then, N. caninum were continuously passaged in these cell lines for 3 months and the effect of host cells on virulence of tachyzoites was assessed by broiler chicken embryonated eggs. Inoculation was performed in the chorioallantoic (CA) liquid of the embryonated eggs with different dilutions (0.5 × 10(4), 1.0 × 10(4), 1.5 × 10(4)) of tachtzoites isolated from these cell cultures. The mortality pattern and pathological changes of the dead embryos and hatched chickens were noted. Tissue samples of brain, liver and heart were examined by histopathological and detection of DNA of parasite by polymerase chain reaction (PCR). Also, consecutive sections of the tissues examined histologically were used for immunohistochemical (IHC) examination. Embryos inoculated with tachyzoites derived from Vero cell line (group V) showed a higher mortality rate (100%) than the embryos that received tachyzoites derived from J774 cell line (group J) (10% mortality rate). The results of this study indicated that the culture of N. caninum in J774 cell led to a marked increase in the number of tachyzoite yields and rapid attenuation in comparison to Vero, so the results were confirmed by IHC and PCR. This study is the first report of the significant effect of host cell on the attenuation of virulence of N. caninum tachyzoites. These findings could potentially provide a practical approach in the mass production of N. caninum tachyzoites, and also in producing live attenuated vaccine.

Toxoplasma gondii antigens: recovery analysis of tachyzoites cultivated in Vero cell maintained in serum free medium

Vero cells have been used successfully in Toxoplasma gondii maintenance. Medium supplementation for culture cells with fetal bovine serum is necessary for cellular growth. However, serum in these cultures presents disadvantages, such as the potential to induce hypersensitivity, variability of serum batches, possible presence of contaminants, and the high cost of good quality serum. Culture media formulated without any animal derived components, designed for serum-free growth of cell lines have been used successfully for different virus replication. The advantages of protozoan parasite growth in cell line cultures using serum-free medium remain poorly studied. Thus, this study was designed to determine whether T. gondii tachyzoites grown in Vero cell cultures in serum-free medium, after many passages, are able to maintain the same antigenic proprieties as those maintained in experimental mice. The standardization of Vero cell culture in serum-free medium for in vitro T. gondii tachyzoite production was performed establishing the optimal initial cell concentration for the confluent monolayer formation, which was 1×10(6) Vero cell culture as initial inoculum. The total confluent monolayer formatted after 96 h and the best amount of harvested tachyzoites was 2.1×10(7) using parasite inoculum of 1.5×10(6) after 7 days post-infection. The infectivity of tachyzoites released from Vero cells maintained in serum-free medium was evaluated using groups of Swiss mice infected with cell-culture tachyzoites. The parasite concentrations were similar to those for mice infected with tachyzoites collected from other infected mice. The data from both in vivo and in vitro experiments showed that in at least 30 culture cell passages, the parasites maintained the same infectivity as maintained in vivo. Another question was to know whether in the several continued passages, immunogenic progressive loss could occur. The nucleotide sequences studied were the same between the different passages, which could mean no change in their viability in the lysate antigen. Thus, the antigen production by cell culture has clear ethical and cost-saving advantages. Moreover, the use of culture media formulated without any human or animal derived components, designed for serum-free growth of cell lines, successfully produced tachyzoites especially for antigen production.

Separation of DNA-containing organelles from Toxoplasma gondii by CZE

Toxoplasma gondii and other members of the family Apicomplexa have two organelles, in addition to the nucleus, that contain DNA. Herein is reported the separation of the DNA-carrying organelles from T. gondii tachyzoites, i.e. the mitochondrion and the apicoplast, by CZE. The cells were stained with SYTO9, a dye that exhibit fluorescence when interacting with double stranded nucleic acids (e.g. DNA) and disrupted by nitrogen cavitation. Following careful removal of the heavier cellular material, the remaining lysate was injected on a CE instrument and the DNA-containing organelles were detected by LIF. The mitochondrion had longer migration time than the apicoplast, and the migration times were comparable in the replicates. This method should potentially also work for other members of the Apicomplexa including Plasmodium falciparum.

Toxoplasma tachyzoites from cell culture are more appropriate in some situations

BACKGROUND

Laboratories traditionally culture toxoplasma tachyzoites in animals for testing and experimental use. This article considers why available cell culture methods are not used more often.

AIM

To compare HeLa cell culture and animal culture for production of toxoplasma tachyzoites.

METHODS

In 2000 HeLa culture replaced animal culture for continuous production of toxoplasma tachyzoites in the Scottish Toxoplasma Reference Laboratory. The performance of animal culture (1994-1998) was compared with HeLa culture (2004-2008). A PubMed search was carried out for 1998 and 2008 to assess the culture methods used in laboratories.

RESULTS

Animal culture was able to produce higher yields of tachyzoites (10(9) from a cotton rat peritoneal harvest compared to 10(7) from a 75 cm(2) cell culture flask) but significantly more HeLa cultures were successful (93% versus 84%; p=0.025). There was no difference in the quality of tachyzoites from animal and HeLa cultures as demonstrated by the high levels of success in the dye test. HeLa culture offered significant advantages in flexibility and control. A review of the literature showed no significant change in the method of culture used in laboratories between 1998 and 2008 (p=0.36).

CONCLUSION

The availability of cell culture methods and the increasingly stringent regulations on the use of animals have not resulted in a decline in the use of animal culture. Animals are necessary for certain experiments but many studies could use cell-culture-derived parasites.

Evaluation of drug effects on Toxoplasma gondii nuclear and plastid DNA replication using real-time PCR

Toxoplasma gondii Nicolle and Manceaux, 1908 is a unicellular protozoan that can infect a broad spectrum of organisms including humans. In addition to a nuclear genome, it also carries a circular DNA within a plastid-like organelle (apicoplast) and a linear genome within its mitochondria. The plastid organelle has been shown to be the target of various anti-parasitic drugs or antibiotics. To evaluate the effects of agents on the DNA replication of T. gondii, we tested six drugs (ciprofloxacin, acetylspiramycin, clindamycin, azithromycin, artemether, and sulfadiazine) on the parasite cultured in Hela cells. After drug treatment for 48 h, the parasite growth and DNA replication were evaluated and quantitated using TaqMan real-time quantitative PCR with oligonucleotide primers synthesized based on a gene from the apicoplast genome (ycf24, Genbank accession no. U87145) and a gene from the nuclear genome (uprt, Genbank accession no. U10246). Our results showed that ciprofloxacin was the most effective in inhibiting the replication of the plastid DNA after 48 h drug treatment, with a reduction of 22% in the copy number of the plastid DNA. Artemether was the most effective drug in suppressing the proliferation of tachyzoites. This study also demonstrates that real-time quantitative PCR is a simple and useful technique for monitoring parasite growth and DNA replication.

Combination of cell culture and quantitative PCR (cc-qPCR) to assess disinfectants efficacy on Cryptosporidium oocysts under standardized conditions

Oocysts of Cryptosporidium parvum are resistant to environmental conditions and many disinfectants. A combination of cell culture and quantitative real time PCR (cc-qPCR) is established for evaluation of anticoccidial disinfectants against C. parvum. C. parvum oocysts were treated with disinfectants, washed and oocysts were incubated with HCT-8 cell monolayers in the presence of excystation medium for 3h. Subsequently, unbound parasites were removed by washing with growing medium and the infected monolayers were further maintained in fresh growing medium for 48h. Genomic DNA was extracted from each sample and qPCR performed targeting a specific sequence of the 70kDa heat shock protein gene in order to quantify development. Treatment of oocysts with cresolic disinfectants demonstrated dose dependent reduction of viability of oocysts. More than 98% inactivations were recorded with at least 2% concentration of cresolic disinfectants after 2h of treatment. Bleach (sodium hypochlorite) at 6% solution induced 92.7% inactivation of C. parvum oocysts after 2h. Thermally treated oocysts (56 and 70 degrees C for 20min) demonstrated complete inactivation, whereas at 38 degrees C no inactivation was observed. Application of Neopredisan((R)) 135-1 and Aldecoc((R)) TGE (4% for 2h) as recommended according to the current guidelines stipulated by DVG (German Veterinary Society) consistently inactivated more than 99.5% of oocysts. The suggested cc-qPCR method appeared to be suited for standardized testing of inactivation measures, particularly for evaluation of chemical disinfectants and thus cc-qPCR is proposed as an alternative to the established chicken infectivity model for Eimeria tenella for testing anticoccidial disinfectants. A minimum inactivation of 99.5% in cc-qPCR model is claimed as a suitable threshold for certification of chemical products for disinfection of coccidia oocysts.

Evaluation of loop-mediated isothermal amplification for detection of Toxoplasma gondii in water samples and comparative findings by polymerase chain reaction and immunofluorescence test (IFT)

The development and evaluation of a 1-step single-tube accelerated loop-mediated isothermal amplification (LAMP) assay for the rapid detection of Toxoplasma in water samples is described. The method has been evaluated based on the amplification of B1 and TgOWP Toxoplasma genes, and it demonstrated a sensitivity detection limit of 0.1 tachyzoites' DNA for both genes. LAMP detection was evaluated and compared with nested polymerase chain reaction (PCR) in 26 water sample pellets spiked with known numbers of Toxoplasma oocysts. After DNA extraction, the detection sensitivity in spiked pellets was 100% by LAMP and 53.8% by PCR. Subsequently, 52 natural water samples of different origin were directly investigated by 3 assays: LAMP, PCR, and immunofluorescence test (IFT). Twenty-five (48%) of 52 have been found positive for Toxoplasma DNA by LAMP, whereas nested PCR products were generated in 7 of 52 (13.5%) water samples. All 52 water samples were negative for Toxoplasma by IFT. These data clearly indicate LAMP as a rapid, specific, and sensitive tool for the detection of Toxoplasma contamination in water samples.

Stress-related and spontaneous stage differentiation of Toxoplasma gondii

Toxoplasma gondii is an obligatory intracellular parasitic protozoan that infects a variety of avian and mammalian hosts including up to one third of the human population worldwide. Developmental differentiation between distinct stages, i.e. sporozoites, tachyzoites and bradyzoites is fundamental for the parasite life cycle and for transmission between hosts. It is also interconnected with the pathogenesis of overt toxoplasmosis and makes T. gondii an important opportunistic pathogen of humans. In order to delineate the underlying mechanisms, several cell culture differentiation systems have been developed which mimic the transition from fast-replicating tachyzoites to slowly proliferating bradyzoites in vitro. Since exogenous stress factors, i.e. alkaline pH, IFN-gamma and other proinflammatory cytokines, chemicals or drugs, heat shock, and deprivation of nutrients have been shown to increase the efficacy of bradyzoite development in vitro, Toxoplasma stage differentiation is largely viewed as a stress-related response to hostile environmental conditions. However, tachyzoite to bradyzoite differentiation also occurs spontaneously in vitro and this raises questions about the importance of stress conditions for triggering stage conversion. High frequencies of spontaneous bradyzoite development in primary and permanent skeletal muscle cells, i.e. cells that preferentially harbour bradyzoite-containing tissue cysts in vivo suggest that the host cell type may be critical. Furthermore, the host cell transcriptome, including the expression of distinct host cell genes, has recently been shown to trigger bradyzoite development and cyst formation. Together, these results strongly indicate that the complex cellular environment, besides exogenous stress factors, may govern the developmental differentiation of T. gondii.

A golden bullet? Selective targeting of Toxoplasma gondii tachyzoites using antibody-functionalized gold nanorods

Conjugates of gold nanoparticles and antibodies have useful functionalities. Here, we show how they can be used to selectively target and destroy parasitic protozoans. Gold nanorods were conjugated with an anti-Toxoplasma gondii antibody and used to target the extracellular tachyzoite which is an infectious form of an obligate parasite Toxoplasma gondii. Subsequent laser irradiation was used to kill the targeted protozoans. This concept provides a new paradigm for the treatment of parasitic protozoans.

Behaviour of Toxoplasma gondii RH Ankara strain tachyzoites during continuous production in various cell lines

Toxoplasma gondii is an obligate intracellular protozoan parasite. The objective of the present study was to examine the behaviour of Toxoplasma gondii RH Ankara strain tachyzoites in a cell culture environment. The study represents the first step in determining whether T. gondii RH Ankara strain tachyzoites, grown in cell culture, are of sufficient quality to allow cessation of in vivo tachyzoite production for diagnostic assays. In the present study, T. gondii RH Ankara strain tachyzoites were continuously produced in myeloma X63.Ag8.653, HeLa, Hep-2, and Vero cell cultures for 2 months. The average size of the tachyzoites was 3×5·7 μm prior to the first inoculation but after continuous production, a marked decrease was noted in average tachyzoite size. The smallest tachyzoite size, was 1×2·1 μm after 2 months, in myeloma cell cultures even though the yield of tachyzoites increased. With other cell cultures, tachyzoite yields were not as high as myeloma cell culture although decrease in size was less. The smallest decrease in tachyzoite size, averaging 2×3·8 μm after 2 months, was observed in tachyzoites produced in HeLa cell cultures. A virulence assay in small groups of BALB/c mice, using tachyzoites derived from cell cultures, was also conducted. The preliminary results of the virulence assay suggest that as the size of the tachyzoites decreased, the virulence in mice decreased. Future research will focus on the effect of the size of cell culture-derived T. gondii RH Ankara strain tachyzoites on the virulence, protein expression, and the reliability of diagnostic assays. Ultimately, the behaviour of tachyzoites from various T. gondii strains will be observed in cell culture to determine if size is altered.

Do Toxoplasma gondii RH strain tachyzoites evolve during continuous passage?

AIM

To examine three lineages of Toxoplasma gondii RH strain in terms of performance in the dye test, culture, and gene expression.

METHODS

Historical data (culture growth and performance in the dye test) from three lineages of RH strain tachyzoites (B, J, and Q) that had been continuously cultured in HeLa cells was assessed. Tachyzoite harvests obtained during continuous cell culture were retrieved from liquid nitrogen and cultured in HeLa cells, providing mRNA that was extracted and used to study gene expression using random amplified polymorphic DNA analysis at different stages of lineage adaptation to continuous culture.

RESULTS

The B and Q lineages consistently produced tachyzoites that were successfully used in the dye test and their gene expression was stable after multiple passages. The J lineage had unpredictable growth, tachyzoites unsuitable for use in the dye test, and changing gene expression with multiple passage.

CONCLUSION

This study has explained some anomalies in the performance of different stocks of T gondii, and suggests that lineages that are still evolving in cell culture should be avoided.

Toxoplasma gondii in vitro culture for experimentation

The aim of this study was to develop a culture method for Toxoplasma gondii that could provide fresh viable tachyzoites as and when required. When T. gondii was continuously maintained in HeLa cell cultures at 37 degrees C, the time to harvest varied from 48 to 144 h. Tachyzoite yields of > or = 1 x 10(6)/ml and > or = 90% viable were obtained from 519/882 (58.8%) cultures and 120/155 (77.4%) harvests were successfully used in the dye test. When cultures were transferred from 37 to 25 degrees C when maximally infected (48-54-h post-infection), they could be stabilised and tachyzoites could be harvested as required, up to 168 h later. When harvested from 25 degrees C, significantly more cultures 783/811 (96.5%) produced tachyzoite yields > or = 1 x 10(6)/ml > or = 90% viable (p < 0.001). Tachyzoite quality also significantly improved and 206/224 harvests (91.9%) (p < 0.001) were successfully used in the dye test. We have demonstrated that tachyzoites can be maintained at dye test quality for at least 7 days in HeLa cultures at 25 degrees C. The system is flexible and robust and provides a means whereby tachyzoites of standard quality can be stored for use in experimental models as and when required.

Culture of protozoan parasites

The in vitro culture of protozoan parasites involves highly complex procedures, which are subject to many variables. These parasites have very complex life cycles and, depending on the life cycle stage, may require different culture parameters. However, in vitro cultivation is important for many reasons, some of which include: diagnosis, antigen and antibody production, assessment of parasite immune modulating capabilities, drug screening, improvements in chemotherapy, differentiation of clinical isolates, determination of strain differences, vaccine production, development of attenuated strains, and the continued supply of viable organisms for studying host-parasite interactions.