Detection in human sera of IgG, IgM and IgA to excreted/secreted antigens from Toxoplasma gondii by use of dot-ELISA and immunoblot assay

Evaluation of Adjuvant Effectiveness of Alum-Propranolol Mixture on the Immunogenicity of Excreted/Secreted Antigens of Toxoplasma gondii RH Strain

Purpose: The introduction of novel adjuvants is an important step in attempts to develop a safe and more efficient vaccine. The present study was performed to determine whether the use of a mixed beta-adrenergic receptor antagonist propranolol (PRP) and aluminum (alum), as an adjuvant, have efficacy for Toxoplasma gondii vaccine to induce protective immunity in a mouse model. Methods: Female BALB/c mice divided into five groups were immunized with excretorys-ecretory antigens (ESA) vaccine, alum-ESA vaccine, PRP-ESA vaccine, and alum-PRP ESA vaccine, as well as with phosphate buffered saline (PBS), as a negative control group. The immune responses were evaluated by lymphocyte proliferation assay for measuring delayedtype hypersensitivity (DTH) response and by cytokine assay for evaluating IFN-γ and IL-5 levels. The survival rate of mice in all groups was assessed during a three-week monitoring period after an intraperitoneal challenge with T. gondii tachyzoites. Results: The results showed that mice immunized with PRP, as an adjuvant, could secret a higher level of IFN-γ, which was significant in comparison to other groups. However, mice vaccinated with alum-precipitated ESA antigen had ability to produce an elevated level of IL-5 compared to other mouse groups (P ≤ 0.05). Moreover, alum-PRP co-administration together with ESA vaccine resulted in the longer survival of mice. Conclusion: The findings of this study revealed that the combination of alum-PRP adjuvants and ESA vaccine of T. gondii elicits both humoral and cellular immune responses, which are comparable to either alum or PRP alone.

Design of Indigenous ELISA Using Tachyzoites from the RH Strain of Toxoplasma gondii and Comparison with Commercial Kits in Ahvaz, Southwest of Iran, 2015

BACKGROUND

Toxoplasma gondii is one of the most common causes of latent infections in humans worldwide. Detecting anti-Toxoplasma antibodies in serum using serological tests is a common method to diagnose toxoplasmosis.

OBJECTIVES

In the present study, an indigenous ELISA kit was prepared using tachyzoites from the RH strain of T. gondii, and its sensitivity and specificity were compared with those of commercial kits.

METHODS

To produce antigens, 0.02 mL of locally isolated T. gondii RH strain parasites along with 10⁹ tachyzoites were injected into the peritoneal cavities of 50 laboratory mice (BALB/C). Parasites were collected after 4 days. After filtering and washing, the concentration of protein in sonicated tachyzoites was calculated using the Lowry protein assay. The dilution of antigen, serum and alkaline phosphatase conjugate was assessed in designing an indigenous ELISA method; then ELISA was performed based on these dilutions, and its sensitivity was determined using 200 serum samples. In addition, the specificity of the assay was evaluated using 40 serum samples from patients with tuberculosis, leukemia or hydatid cyst.

RESULTS

Indigenous ELISA was used to examine 100 serum samples containing anti-T. gondii IgG, with a sensitivity of 98% (commercial kits: 100%). Another 100 serum samples containing anti-T. gondii IgM were also tested, with a sensitivity of 99% (commercial kits: 100%). When 40 serum samples from patients with leukemia, hydatid cyst or tuberculosis were examined using anti-T. gondii IgG, the specificity was 100%, identical to commercial kits. However, the specificity of a similar test with anti-T. gondii IgM was just 28.6% for serum samples from leukemia patients, 21.4% for hydatid cyst and 16.7% for tuberculosis.

CONCLUSIONS

We found that purified locally isolated soluble crude antigens of the RH strain of T. gondii from the peritoneal cavity of mice may be one of the most promising antigens for detection of human toxoplasmosis in routine screening.

Evaluation of Toxoplasma gondii soluble, whole and excretory/secretary antigens for diagnosis of toxoplasmosis by ELISA test

The present study was performed to compare the soluble, whole and excretory/secretary antigens of Toxoplasma gondii (RH strain) in diagnosis of toxoplasmosis by ELISA method. Tachyzoites of T. gondii, RH strain were injected in intra-peritoneal cavity of BALB/c mice, after 4 days tachyzoites were harvested by peritoneal washing of the mice. For soluble antigen, exudates were centrifuged and sediment sonicated and then centrifuged at 4 °C, 1 h, supernatant collected and density of protein determined by Bradford method. For whole antigen after collecting, washing and centrifuging of peritoneal fluid the tachyzoites sediment was counted. In excretory/secretary antigen 1.5 × 10⁸ tachyzoites were transferred in 1 ml tube of saline and incubated under mild agitation and after centrifuging, supernatant was collected and protein density determined by Bradford method. 176 human serum samples were evaluated for T. gondii IgG antibody with prepared antigens, and finally serum samples were evaluated by commercial ELISA kit (Trinity, USA) which was considered as gold standard method. In this study sensitivity and specificity of prepared antigens compared with commercial kit in ELISA method. Sensitivity and specificity of soluble antigen was 91.4 and 74.5 %, in whole antigen these parameters were 77.1 and 77.3 % and in excretory/secretary antigen were 28.5 and 74.5 % respectively. Soluble antigen had high levels of sensitivity and specificity in ELISA method and the results were rather resemble to commercial kit (Trinity, USA).

A comparative study between excretory/secretory and autoclaved vaccines against RH strain of Toxoplasma gondii in murine models

Toxoplasma gondii is an obligate intracellular protozoan that has a major importance in public health, in addition to veterinary medicine. Therefore, the development of an effective vaccine for controlling toxoplasmosis is an important goal. Excretory/secretory antigens (ESA), were previously identified as potential vaccine candidates, proved to play important roles in the pathogenesis and immune escape of the parasite. In addition, autoclaved Toxoplasma vaccine (ATV) is a special type of killed vaccine, recently characterized. The aim of the present work was, to compare between excretory/secretory and ATV against RH strain of T. gondii in mice based on; parasitological and histopathological levels. Tachyzoites were harvested from peritoneal exudates of infected mice and were used for challenge infection and vaccine preparation. BCG was used as an adjuvant. Mice were allocated equally into five groups; they were vaccinated intradermally over the sternum. The results of this study showed that the survival time after challenge, extended up to 16 days in ESA vaccinated group and up to 15 days in autoclaved Toxoplasma vaccinated group. ESA vaccinated group exhibited a profound decrease in parasite load following parasite challenge with a higher percentage of reduction in parasite count in all examined organs than the autoclaved Toxoplasma vaccinated group. The histopathological picture of the liver in both immunized groups, revealed marked reduction in the pathological changes observed as compared to controls, especially in ESA vaccinated group. It was concluded that vaccination with ESA showed more promising results versus ATV, as demonstrated by the survival rate of vaccinated mice, tachyzoites count and histopathological examination.

Mast cells modulate acute toxoplasmosis in murine models

The role of mast cells (MCs) in Toxoplasma gondii infection is poorly known. Kunming outbred mice were infected intraperitoneally with RH strain T. gondii, either treated with compound 48/80 (C48/80, MC activator) or disodium cromoglycate (DSCG, MC inhibitor). Compared with infected controls, infected mice treated with C48/80 exhibited significantly increased inflammation in the liver (P < 0.01), spleen (P < 0.05), and mesentery (P < 0.05) tissues, higher parasite burden in the peritoneal lavage fluids (P < 0.01), and increased levels of mRNA transcripts of T. gondii tachyzoite surface antigen 1 (SAG1) gene in the spleen and liver tissues (P < 0.01), accompanied with significantly increased Th1 cytokine (IFN-γ, IL-12p40, and TNF-α) (P < 0.01) and decreased IL-10 (P < 0.01) mRNA expressions in the liver, and increased IFN-γ (P < 0.01) and IL-12p40 (P < 0.01) but decreased TNF-α (P < 0.01) and IL-4 (P < 0.01) in the spleens of infected mice treated with C48/80 at day 9-10 p.i. Whereas mice treated with DSCG had significantly decreased tissue lesions (P < 0.01), lower parasite burden in the peritoneal lavage fluids (P < 0.01) and decreased SAG1 expressions in the spleen and liver tissues (P < 0.01), accompanied with significantly increased IFN-γ (P < 0.01) and IL-12p40 (P < 0.05) in the liver, and decreased IFN-γ (P < 0.05) and TNF-α (P < 0.01) in the spleens; IL-4 and IL-10 expressions in both the spleen and liver were significantly increased (P < 0.01) in the infected mice treated with DSCG. These findings suggest that mediators associated with the MC activation may play an important role in modulating acute inflammatory pathogenesis and parasite clearance during T. gondii infection in this strain of mice. Thus, MC activation/inhibition mechanisms are potential novel targets for the prevention and control of T. gondii infection.

Toxoplasma gondii excretory secretory antigenic proteins of diagnostic potential

Infection with Toxoplasma gondii is widespread and important in humans, especially pregnant women and immunosuppressed patients. A panel of tests is usually required for diagnosis toxoplasmosis. Excretory secretory antigen (ESA) is highly immunogenic, and thus it is a good candidate for investigation into new infection markers. ESA was prepared from tachyzoites of RH strain of T. gondii by mice intraperitoneal infection. Sera were obtained from several categories of individuals who differed in their status of anti-Toxoplasma IgM, IgG and IgG avidity antibodies. The ESA was subjected to SDS-PAGE, two-dimensional gel electrophoresis and Western blot analysis. Antigenic bands of approximate molecular weights of 12, 20 and 30 kDa, when probed with anti-human IgM-HRP and IgA-HRP, showed good potential as infection markers. The highest sensitivity of the bands was 98.7% with combination of IgM and IgA blots with sera of patients with anti-Toxoplasma IgM+ IgG+. The specificities were 84% and 70% with sera from other infections and healthy controls in IgM blots and IgA blots respectively. By mass spectrometry, the 12 kDa protein was identified as thioredoxin. The two top proteins identified for 20 kDa molecule were microneme protein 10 and dense granule protein 7; whereas that for 30 kDa were phosphoglycerate mutase 1 and phosphoglycerate mutase.

Evaluation of excreted/secreted antigens derived from peritoneal of toxoplasma infected small mice to detect IgG against Toxoplasma

The present study, evaluated, using the components of peritoneal fluid of infected mice (as another source of E/SA), for the detection of Toxoplasma specific IgG in human serum. Peritoneal fluids of mice infected by intraperitoneal (IP) inoculation of Toxoplasma tachizoites were collected after 3 days and centrifuged at 750 x g for 15 min then the supernatant was precipitated with ammonium sulphate solution (40% saturated) and used as components containing E/SA. Forty nine uninfected (without anti-Toxoplasma antibodies) and thirty two positive (with IgG to Toxoplasma) human serum samples were selected (all sera were first tested by standard method for detection of IgG antibodies anti-T. gondii) then the sera were tested by ELISA using E/SA. The cut-off point with 95% confidences was found to be 0.78. Moreover, sensitivity and specificity of the method were determined to be 84 and 92%, respectively. The present results indicate that peritoneal exudates from mice infected with T. gondii may be used as a source of antigenic material for the detection of Toxoplasma-specific IgG and may be valuable for the development of new tools in the serodiagnosis of toxoplasmosis.

Toxoplasma gondii and mast cell interactions in vivo and in vitro: experimental infection approaches in Calomys callosus (Rodentia, Cricetidae)

In the present work, we studied some qualitative and quantitative characteristics of mast cells located in the peritoneal cavity, submandibular and dorsal lymph nodes and ileum of Calomys callosus experimentally infected by Toxoplasma gondii. In uninfected animals, the majority of mast cells had similar ultra-structural characteristics, including several cytoplasmic granules with homogeneous and electron dense contents. However, after 1 h of infection, a significant influx of mast cells into peritoneal cavity was observed. The number of mast cells in this compartment decreased progressively in infected animals, and was significantly lower than the number of mast cells in control animals after 48 h of infection. Mast cells from infected animals or from purified suspensions that were infected in vitro presented significant morphological modifications, suggesting a degranulation process: cytoplasmic granules with electron dense content, fusion of the cytoplasmic granules, intracytoplasmic channels, cytoplasmic granules with flocculent material, plasma membrane rupture and granule contents in the extracellular environment. A remarkable increase in the influx of neutrophils toward the peritoneal cavity of the infected animals was observed after 12 h of infection. Moreover, this event occurred after the mast cell degranulation process took place. The relative increase in the number of mast cells and neutrophils was also followed by an increase in the number of macrophages, but there was a significant decrease in lymphocyte influx. After 48 h of infection, the parasite had spread from the peritoneal cavity to all organs examined. Also, mast cells from these organs showed evident morphological alterations, indicating the presence of the degranulation process. These results suggest that mast cells are deeply involved with the acute phase of the inflammatory response in this experimental model.

Immune responses against excreted/secreted antigens of Toxoplasma gondii tachyzoites in the murine model

In the present study, excretory secretory antigens (ESA) of Toxoplasma gondii were evaluated in immunization of 8-10 week inbred female Balb/c mice. Tachyzoites of the parasite were cultured in cell-free incubation medium (RPMI-1640), and then supernatant of the medium was loaded on an ion-exchange chromatography column. Two fractions (ESA-F(1) and ESA-F(2)) were collected from the column. For immunization of the mice, 50 were allocated into 5 groups of 10. The first, second, third, and fourth groups were immunized, twice with total-ESA, ESA-F(1), ESA-F(2) or toxoplasma lysate antigen (TLA), respectively. The fifth group was selected as a negative control group (non-immunized). The virulent RH strain of Toxoplasma gondii was used to challenge. Delayed-type hypersensitivity responses (DTHs) were measured by intra-footpad injection measuring induration at timed intervals. Lymphocyte transformation tests (LTTs) were done on lymph node cells using [3H] thymidine incorporation as an indication of reactivity. Peritoneal macrophages from sensitized mice were stimulated and nitric oxide was measured by Griess method. The ESA-F(1) and ESA-F(2) fractions were separated on poly acrylamide gel electrophoresis (PAGE) and SDS-PAGE. ESA-F(1) had 4 bands on PAGE and 14 bands on SDS-PAGE. ESA-F(2) had one band on PAGE and two bands on SDS-PGE. Sensitized mice showed DTH and lymphocyte transformation responses to total-ESA, ESA-F(1), and ESA-F(2) and peritoneal macrophages produce nitric oxide following stimulation. In challenge experiments, all non-immunized mice died within 10 days, whereas immunized mice survived for longer time periods (P<0.05). The highest survival rate was observed in mice that immunized with ESA-F(2). We suggest that these antigens especially ESA-F(2) should be of value for the development of new strategies for immunization against toxoplasmosis.

Dissecting the IgM antibody response during the acute and latent phase of toxoplasmosis

A major problem in anti-toxoplasma IgM serology is the occurrence of clinically non-relevant (CNR) IgM in sera of latently infected (LI) individuals. The susceptibility for CNR IgM of the Toxo ISAGA IgM, Platelia Toxo IgM and Vidas Toxo IgM assays was determined using sera of LI individuals with an IgM titer in the Abbott IMx Toxo IgM assay. The specificity of CNR-IgM and IgM antibodies in sera of acutely infected (AI) individuals was compared by immunoblotting.Seven/19 samples with CNR IgM antibodies were found positive in the ISAGA IgM, compared with 16/19 and 17/19 with the Vidas and Platelia Toxo IgM assays, respectively. In contrast, immunoblotting allowed a distinction between CNR IgM and AI IgM antibodies of the 30 sera studied.Clearly, IgM assays are susceptible to CNR IgM antibodies. In cases of doubt, immunoblotting is of value as confirmation method. Because CNR IgM antibodies are specific for toxoplasma, it will be difficult to improve IgM ELISAs in such a way that CNR IgM antibodies will not interfere with the analysis.