Purification of Toxoplasma antigen for hemagglutination tests

Simple hemagglutination inhibition test for the diagnosis of toxoplasmosis

A simple hemagglutination inhibition (HI) test for the serological diagnosis of toxoplasmosis has been developed and evaluated. A total of 84 human and 120 mouse serum samples were tested by the newly developed HI test and compared with an immunoglobulin G-indirect fluorescent antibody test. Statistical analysis of serum titers obtained by using the HI test and the immunoglobulin G-indirect fluorescent antibody test showed a correlation coefficient of 0.89. The diagnostic efficacy of HI when compared with the immunoglobulin G-indirect fluorescent antibody diagnostic test results was 96.43% for human sera and 100% for mouse sera. The unique hemagglutination antigen, derived from Toxoplasma gondii (Rh strain) exotoxin, spontaneously binds with mouse or rat erythrocytes, causing the hemagglutination reaction. In this study, 2, 4, or 8 hemagglutinating units of T. gondii exotoxin was used with Swiss/Webster mouse erythrocytes as an indicator for the HI assay. The results indicate that 8 hemagglutinating units is optimal because this concentration has the least unexplained variability. T. gondii exotoxin was stable for at least 18 months at -70 degrees C. The Toxoplasma HI test we report in this paper is shown to be a fast, easy, highly specific, and sensitive test for the diagnosis of toxoplasmosis.

The antigenic structure of Toxoplasma gondii: a review

Even though T. gondii is ubiquitous in the animal kingdom, definitive information on its antigenic structure has only become available over the last few years, largely as a result of recent advances in immunology and biochemistry. New knowledge in this area will enable the immune response to the parasite to be studied in greater detail and may lead to the development of newer, more meaningful diagnostic tests for toxoplasmosis, and possibly a vaccine against it. This paper reviews knowledge on the antigenic structure of this extremely widespread and important protozoan parasite.

Immunoenzymatic detection of three kinds of 43,000-molecular-weight antigens by monoclonal antibodies in the insoluble fraction of Toxoplasma gondii

Monoclonal antibodies (TpM 3, TpM 6, and TpM 19) against Toxoplasma gondii insoluble antigens were produced by the hybridization of NS-1, a mouse myeloma cell line, with spleen cells from mice immunized with T. gondii insoluble antigens. TpM 3, TpM 6, and TpM 19 were characterized by the dye test, the latex agglutination test, two types of enzyme-linked immunosorbent assays, using either T. gondii supernatant antigens or T. gondii insoluble antigens, and immunoperoxidase staining. TpM 3, TpM 6, and TpM 19 antigens were analyzed by the immunoblotting method, using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrophoretic transfer of the antigens to nitrocellulose sheets. TpM 3, TpM 6, and TpM 19 were all negative by the dye test, the latex agglutination test, and the enzyme-linked immunosorbent assay, using T. gondii supernatant antigens but positive by the enzyme-linked immunosorbent assay, using T. gondii insoluble antigens. Each antibody gave unique spot patterns in the cytoplasm of tachyzoites, and each detected antigens of ca. 43,000 molecular weight with different electrophoretic patterns. Purified TpM 3 antigen bound only to TpM 3 but not to TpM 6 or TpM 19. Comparable results were obtained with TpM 6 and TpM 19 antigens. Rabbit anti-T. gondii sera reacted with both TpM 3 and TpM 19 antigens. However, human anti-T. gondii sera reacted only with TpM 3 antigen. These results indicate that T. gondii insoluble antigens contained at least three types of 43,000-molecular-weight antigens that have been revealed for the first time in this paper.

Ultrastructural and biochemical studies on the immunohistochemistry of Toxoplasma gondii antigens using monoclonal antibodies

To determine the cellular distribution of Toxoplasma antigens, RH strain tachyzoites were incubated with either one of three monoclonal antibodies (FMC 19, FMC 20, FMC 22) to T. gondii, or one of two controls (the murine myeloma protein MOPC 21, or phosphate buffered saline), and then incubated with peroxidase-labelled goat-antimouse IgG. Diaminobenzidine was added as substrate and electron microscopy was used to localize the reaction. All three antibodies bound to the entire periphery of the tachyzoite surface membrane. To ascertain the chemical composition of the antigens against which seven monoclonal antibodies (FMC 18, FMC 19, FMC 20, FMC 22, FMC 23, 2G11, 3E6) to T. gondii reacted, untreated, pronase-treated, or periodate-treated tachyzoites were incubated with the antibodies or MOPC 21, and then with [125I]-Protein A. The pronase-treated tachyzoites showed reduced binding for six of the antibodies, compared with the reduction in binding of MOPC 21 with the pronase-treated parasites. The periodate-treated tachyzoites had reduced binding for FMC 18 only. The results of these experiments confirm that most Toxoplasma surface antigens are protein in nature, and are consistent with the hypothesis that at least one cytoplasmic antigen is secreted onto the parasite cell surface.

An investigation of the antigenic structure of Toxoplasma gondii

Mechanical fragmentation has been the prime method for preparing soluble Toxoplasma gondii antigens for use in serodiagnosis. The three methods most commonly used (lysis-in-water, sonication and freeze-thawing) all yielded three antigenic peaks (4, 5 and 6) on crossed immunoelectrophoresis. Antigen 6 has been shown to be heat stable (56 degrees C/1 h) and appears to be a major antigen in the indirect haemagglutination test (IHAT). Saponin and octyl glucoside were found to be the most effective detergents for solubilization when used in combination, yielding between 7 and 11 antigens. Using a new triple-staining technique, antigen 3 has been characterized as a glycoprotein, antigen 7 as a lipopolysacchiaride and antigens 1, 2, 4, 5, 6 and 8 to 11 as proteins. Molecular weight determination by gel filtration has been carried out and the majority of the antigens have a mol. wt of 10(5) to 1.5 x 10(5) daltons. Crossed immunoelectrofocusing has shown that all the antigens are isoelectric at acidic pH. The findings of this preliminary investigation into the basic antigenic structure of T. gondii are discussed in relation to future work and the rational development of serodiagnostic tests.

[Serological studies on rabbits inoculated with Toxoplasma gondii]

Serological studies on toxoplasmosis were conducted with rabbits sera that were immunized with RH strain or infected with Beverley strain of Toxoplasma gondii. Complement fixation tests, agar-gel double diffusion tests and agar-gel immunoelectrophoresis were performed. Toxoplasma crude antigen was prepared from the organisms in mice peritoneal fluids, which were infected with RH strain of Toxoplasma gondii. The organisms were suspended in saline volume originally exudated and counted in hemocytometer for purity of the organisms over 99%. These suspended organisms were prepared by sonication, and the solution was centrifuged for 30 min. at 10,000 rpm in 4 degrees C. These supernatant fluids were used as crude antigen. On the other hand, purified antigens were fractionated on Sephadex G-200 gel filtration. A Sephadex G-200 column, 80 by 4 cm, equilibrated with Tris-HCl-(0.1M)-NaCl (1.0M) buffer, pH 8.0 was used. The eluate fractions were collected in 3 ml per hour and the absorbance at 280 nm was measured with a Beckman Du-2 spectrophotometer. Each tube is pooled into 6 fractions by protein density graph. For immunization of rabbits, crude antigen of RH strain was emulsified with an equal amount of incomplete Freund's adjuvant and l ml of mixture was injected subcutaneously into them once a week for 5 successive weeks. Antisera were obtained at an interval of a week, beginning the first week after the last immunization, while several rabbits were infected with Beverley strain of Toxoplasma gondii by inoculating about 200 cysts and antisera were obtained from them serially at a week interval. The results were as follows: 1. The sera from the rabbits immunized with the RH strain or infected with Beverley strain of Toxoplasma gondii againist the crude antigen showed the first positive reactions in 2 or 3 weeks after the administration or immunization in complement fixation tests. Maximum titers appeared in 4 or 5 weeks after immunization with RH strain and in 7 or 9 weeks after infection with Beverley strain respectively. 2. Complement fixation tests showed the positive reactions in the rabbits sera immunized with RH strain against the purified antigens II, III, IV, V and VI: moreover, antigen IV fraction showed the highest titer. On the other hand in the rabbits sera infected with Beverley strain against the purifed antigens II, III and IV fractions showed the positive reaction; especially, antigen fraction IV showed the highest titer. 3. In immuno-diffusion tests, the sera from the rabbits immunized with RH strain and infected with Beverley strain, against the crude antigen appeared the precipitin bands 2 weeks after the immunization or infection. And the former showed the 2 or 5 precipitin bands after 5-8 weeks and the latter showed the l or 2 precipitin bands after 6 weeks. 4. The sera from the rabbits immunized with RH strain against the purified antigens II, III, IV,V and VI showed the precipitin bands, and the sera from the rabbits infected with Beverley strain against the purified antigens II, III and IV showed the precipitin bands in the immuno-diffusion tests. Especially antigen IV was the strongest reaction against the sera from RH strain and Beverley strain. 5. In agar-gel immunoelectrophoresis, the immunized sera against the crude antigen showed 8 arcs. But the infected sera against the crude antigen showed 4 or 5 arcs. 6. The immunized sera against the fractionated antigens II, III, IV, V, VI showed arcs, but against the fractionated antigen IV showed 6 arcs and in the antigens II, III, V, VI showed l or 2 arcs only. On the other hand, the infected sera against the fractionated antigens IV showed 4 arcs, II and III showed the l arcs, which was the most weak of all.