Toxoplasma gondii in vitro culture for experimentation

Diagnostic methods and protocols used in investigating Toxoplasma gondii in humans: A review

Toxoplasmosis, a zoonotic disease, is a parasitic infection caused by a coccidian protozoan Toxoplasma gondii. In immunocompetent people, the infection is asymptomatic, while it can produce serious signs in immunocompromised people and in developing fetuses. Accurate diagnosis is dependent, mainly, on the clinical features. However, in immunocompromised patients, the diagnosis is very difficult and may lead to misdiagnosis and improper treatment. Today, molecular diagnosis and serotyping are widely used for the diagnosis of T. gondii in many countries. The aim of the present short review is to highlight the current diagnostic methods and protocols that are used for the diagnosis of T. gondii in humans.

Introduction of protocols for mass production of Toxoplasma gondii tachyzoites of the genotype II PRU strain

Background

Few investigations of genotype II of Toxoplasma gondii, the most prevalent form of the Toxoplasma parasite in humans, have been carried out on due to the rapid conversion of tachyzoites to bradyzoites in its life cycle. The current study aimed to create animal and in vitro models for production of the tachyzoites of the Prugniaud (PRU) genotype II strain.

Methods

To develop an immunocompromised model and obtain tachyzoites of the PRU strain, BALB/c mice were orally treated with dexamethasone (10 mg/kg), cyclophosphamide (36 mg/kg), and cyclosporine (18 mg/kg) from 5 days prior to inoculation. Then, 10-15 tissue cysts of PRU strain were inoculated intraperitoneally into the mice. The tachyzoites obtained from mice were then cultivated in a HeLa cell culture. The resulting yield of tachyzoites was cryopreserved in 92% fetal calf serum, 8% dimethyl sulfoxide. The infectivity of these tachyzoites was evaluated using in vivo and in vitro examinations.

Results

Numerous tachyzoites were observed in the peritoneal fluid of the immunosuppressed mice within 10-15 days after inoculation, and many tachyzoites were harvested from the HeLa cell culture. Trypan Blue staining showed 80% viability of the tachyzoites recovered from cryopreservation and this was confirmed by HeLa cell culture. In addition, mice infected intraperitoneally with the recovered tachyzoites presented with cysts in the brain after 2 months.

Conclusion

We have developed an animal model for mass production of T. gondii tachyzoites of the PRU strain. This method can provide fresh viable tachyzoites of Toxoplasma gondii for use as and when required in future investigations.

Age-related changes in cerebral congenital toxoplasmosis: Histopathological and immunohistochemical evaluation

Congenital toxoplasmosis is a widespread worldwide disease producing varying degrees of damage to the fetus including ocular and neurological impairment. However, the underlying mechanisms are not yet clear. Therefore, the current study aimed to investigate the progress of congenital cerebral toxoplasmosis in experimentally infected offspring animal model at different age groups till become adults. To fulfill this aim, the offspring of Me49 T. gondii infected pregnant mice were divided into groups; embryo, infant, young and adult phases. Blood and brain samples were collected for further hormonal and histopathological studies and immunohistochemical staining of glial fibrillary acidic protein (GFAP) and synaptophysin (SYN). Our results showed several encephalitic changes in the infected groups ranging from gliosis to reduced cortical cell number and fibrinoid degeneration of the brain. We showed increased expression of GFAP and SYN indicating activation of astrocytes and modification of the synaptic function, respectively. These changes started intrauterine following congenital infection and increased progressively afterward. Moreover, infected mice had elevated corticosterone levels. In conclusion, the current study provided new evidences for the cellular changes especially in the infected embryo and highlighted the role of GFAP and SYN that may be used as indicators for T. gondii-related neuropathy.

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.

Primary culture of cat intestinal epithelial cells in vitro and the cDNA library construction

Felids are the only definitive hosts of Toxoplasma gondii. To lay a foundation for screening the T. gondii-felids interaction factors, we have developed a reproducible primary culture method for cat intestinal epithelial cells (IECs). The primary IECs were isolated from a new born cat's small intestine jejunum region without food ingress, and respectively in vitro cultured by tissue cultivation and combined digestion method with collagenase XI and dispase I, then purified by trypsinization. After identification, the ds cDNA of cat IECs was synthesized for constructing pGADT7 homogenization three-frame plasmid, and transformed into the yeast Y187 for generating the cDNA library. Our results indicated that cultivation of primary cat IECs relays on combined digestion to form polarized and confluent monolayers within 3 days with typical features of normal epithelial cells. The purified cells cultured by digestion method were identified to be nature intestinal epithelial cells using immunohistochemical analysis and were able to maintain viability for at least 15 passages. The homogenizable ds cDNA, which is synthesized from the total RNA extracted from our cultured IECs, distributed among 0.5-2.0 kb, and generated satisfying three-frame cDNA library with the capacity of 1.2 × 106 and the titer of 5.2 × 107 pfu/mL. Our results established an optimal method for the culturing and passage of cat IECs model in vitro, and laid a cDNA library foundation for the subsequent interaction factors screening by yeast two-hybrid.

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: 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.

Identification of genes expressed during Toxoplasma gondii infection by in vivo-induced antigen technology (IVIAT) with positive porcine sera

Infection of pigs with Toxoplasma gondii is a common source of human toxoplasmosis and causes serious economic losses. In vivo-induced antigen technology (IVIAT) is an effective immunological technique to identify the antigens that a pathogen specifically expressed during infection. To discover the genes that are important in T. gondii infection of pigs, we employed IVIAT using sera from infected pigs. Fourteen antigens were identified including microneme protein 11 (MIC11), dense granule protein 5 (GRA5), 18 kDa cyclophilin (C-18), serine proteinase inhibitor (PI), calmodulin (CaM), leucine-rich repeat protein ( LRRP), D-3-phosphoglycerate dehydrogenase (D3PD), elongation factor 1-gamma (EF1), and 6 hypothetical proteins. The increased transcription levels of 5 (MIC11, GRA5, C-18, PI, and CaM) of the 14 molecules identified by IVIAT were confirmed by real-time PCR. The full length or partial proteins encoded by these 5 genes were expressed in Escherichia coli , and their immunogenicity was confirmed by Western blot analysis with positive porcine sera. Further functional studies were conducted with CaM. Suppression of CaM expression by RNA interference decreased T. gondii tachyzoites cell attachment, invasion, and egress but did not influence their replication. The proteins identified in this study are predicted to be involved in cell invasion, ion-protein binding, protein folding, biosynthesis, and metabolism. The results of the functional analysis support the hypothesis that CaM contributes to parasite pathogenesis during infection. These results may have significant implications for the discovery of candidate molecules for the development of potential therapies and preventive measures against toxoplasmosis in pigs.

A review on human toxoplasmosis

Toxoplasmosis is a worldwide infection caused by the intracellular parasite Toxoplasma gondii. At least a third of the world human population are infected with the parasite, making it one of the most successful parasitic infections. Primary maternal infection may cause health-threatening sequelae for the foetus, or even cause death in uterus. Reactivation of a latent infection in immune deficiency conditions such as AIDS and organ transplantation can cause fatal toxoplasmic encephalitis. Toxoplasmosis is a major cause of retinochoroiditis, especially in individuals with an impaired immune system. Despite the usually 'asymptomatic' nature of the infection, a significant burden imposed by the parasite necessitates the implementation of effective means for the prevention, diagnosis, and management of this disease. Laboratory diagnosis, i.e. PCR and serologic assays, plays the main role in the diagnosis of congenital infection and assists in the confirmatory diagnosis of toxoplasmic encephalitis and ocular toxoplasmosis. Here, we briefly review general aspects of Toxoplasma infection and focus on the diagnostic methods currently used in medical laboratories for the diagnosis of Toxoplasma infection.

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.

Significant reduction of brain cysts caused by Toxoplasma gondii after treatment with spiramycin coadministered with metronidazole in a mouse model of chronic toxoplasmosis

Toxoplasma gondii is a parasite that generates latent cysts in the brain; reactivation of these cysts may lead to fatal toxoplasmic encephalitis, for which treatment remains unsuccessful. We assessed spiramycin pharmacokinetics coadministered with metronidazole, the eradication of brain cysts and the in vitro reactivation. Male BALB/c mice were fed 1,000 tachyzoites orally to develop chronic toxoplasmosis. Four weeks later, infected mice underwent different treatments: (i) infected untreated mice (n = 9), which received vehicle only; (ii) a spiramycin-only group (n = 9), 400 mg/kg daily for 7 days; (iii) a metronidazole-only group (n = 9), 500 mg/kg daily for 7 days; and (iv) a combination group (n = 9), which received both spiramycin (400 mg/kg) and metronidazole (500 mg/kg) daily for 7 days. An uninfected control group (n = 10) was administered vehicle only. After treatment, the brain cysts were counted, brain homogenates were cultured in confluent Vero cells, and cysts and tachyzoites were counted after 1 week. Separately, pharmacokinetic profiles (plasma and brain) were assessed after a single dose of spiramycin (400 mg/kg), metronidazole (500 mg/kg), or both. Metronidazole treatment increased the brain spiramycin area under the concentration-time curve from 0 h to ∞ (AUC(0-∞)) by 67% without affecting its plasma disposition. Metronidazole plasma and brain AUC(0-∞) values were reduced 9 and 62%, respectively, after spiramycin coadministration. Enhanced spiramycin brain exposure after coadministration reduced brain cysts 15-fold (79 ± 23 for the combination treatment versus 1,198 ± 153 for the untreated control group [P < 0.05]) and 10-fold versus the spiramycin-only group (768 ± 125). Metronidazole alone showed no effect (1,028 ± 149). Tachyzoites were absent in the brain. Spiramycin reduced in vitro reactivation. Metronidazole increased spiramycin brain penetration, causing a significant reduction of T. gondii brain cysts, with potential clinical translatability for chronic toxoplasmosis treatment.

Toxoplasma gondii: determination of the onset of chronic infection in mice and the in vitro reactivation of brain cysts

Toxoplasma gondii is an intra-cellular parasite that infects humans through vertical and horizontal transmission. The cysts remain dormant in the brain of infected humans and can reactivate in immunocompromised hosts resulting in acute toxoplasmic encephalitis which may be fatal. We determined the onset and progression of brain cysts generation in a mouse model following acute toxoplasmosis as well as the ability of brain cysts to reactivate in vitro. Male Balb/c mice, (uninfected control group, n = 10) were infected orally (study group, n = 50) with 1000 tachyzoites of T. gondii (ME49 strain) and euthanized at 1, 2, 4, 8 and 16 weeks post infection. Brain tissue was harvested, homogenized, stained and the number of brain cysts counted. Aliquots of brain homogenate with cysts were cultured in vitro with confluent Vero cells and the number of cysts and tachyzoites counted after 1 week. Brain cysts but not tachyzoites were detected at week 2 post infection and reached a plateau by week 4. In vitro Vero cells culture showed similar pattern for cysts and tachyzoites and reactivation of cyst in vitro was not influenced by the age of the brain cysts.

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.

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.