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

Identification and biochemical characterization of antigens of tachyzoites and bradyzoites of Toxoplasma gondii with cross-reactive epitopes

The aim of the present work was the identification and biochemical characterization of antigens from the tachyzoite and bradyzoite stages of Toxoplasma gondii that share cross-reactive epitopes. Our previous work has demonstrated the induction by tachyzoite excreted-secreted antigens of both a humoral and a cell-mediated protective response. We investigated the question as to whether some bradyzoite and tachyzoite (excreted-secreted, soluble or membrane) antigens share cross-reactive epitopes. Using immunoprecipitation techniques, we identified four tachyzoite antigens with molecular weights of 63, 43, 39, and 28.5 kDa, which were recognized both by sera raised against tachyzoite antigens and by chronic-phase human sera with residual IgG antibodies. In an attempt to define the biochemical nature of these antigens, we show that the 43- and 28.5-kDa antigens seem to be glycosylated since they bind to concanavalin A, as does a 37-kDa tachyzoite antigen.

Toxoplasma gondii: characterization of monoclonal antibodies that recognize rhoptries

We have previously reported on a series of monoclonal antibodies that recognize the rhoptries of Toxoplasma gondii and that interfere with the action of penetration enhancing factor. The antibodies immunoprecipitate several related antigens from [35S]methionine-labeled parasites that range in size from 60 to 43 kDa. By immunoblot, one of the antibodies reacts with the 60 kDa protein in the presence of protease inhibitors. Trypsin digestion of the antigen destroyed antigenic reactivity indicating that the 60 kDa antigen is a protein. The antigen was stable to periodate oxidation and failed to react with Schiff's reagent, indicating that the antigen contains little or no carbohydrate. Two-dimensional gel electrophoresis followed by immunoblot showed that the antigen recognized by Tg 49 was an acidic protein with an approximate pI of 5.8.

Efforts towards a vaccine against Toxoplasma gondii: a review

In a review, past as well as present investigations carried out towards a vaccine against toxoplasmosis are outlined. A historical retrospect of the various immunization experiments is given, recent research projects intending the characterization of antigens that are relevant to host protective immunity are described, and a prospect to future problems and developments expected in the field is drafted.

Ultrastructural localization of an intracellular Toxoplasma protein that induces protection in mice

We report the ultrastructural localization of Toxoplasma antigens recognized by monoclonal antibody F3G3, which protects mice against lethal challenge. By using colloidal immunogold labeling, F3G3 failed to react with the surface of intact Toxoplasma cells, confirming previous observations that it recognizes an intracellular antigen. Immunoperoxidase labeling with F3G3 was obtained only when Toxoplasma cells were previously exposed to Triton X-100. A specific immunoperoxidase reaction was located beneath the surface membrane in the region of the pellicle and within the elaborate network of vesicles which are extruded from the surface of Toxoplasma cells during entry into host cells. Similar results were obtained with mouse polyclonal sera and a second monoclonal antibody, 6-86-1E11, both of which were produced against the F3G3 affinity-purified protein. The location of the epitope recognized by F3G3 was confirmed by purifying T. gondii-derived surface membrane vesicles, separating these proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and immunoblotting. Monoclonal antibody 6-86-1E11 and the analogous polyclonal sera reacted with the antigenically related proteins of 58 and 28 kilodaltons that were found both in the intact organisms and in the purified surface membrane vesicles. These results indicate that the epitope recognized by F3G3 is located beneath the Toxoplasma cell surface membrane and is contained within plasma membrane-derived vesicles.

The immunocytochemical demonstration of Toxoplasma antigen in the brains of congenitally infected mice

The peroxidase anti-peroxidase immunocytochemical staining method was used to identify Toxoplasma antigen in paraffin embedded sections of the brains of 22 mice congenitally infected with the parasite. Intact Toxoplasma tissue cysts were readily demonstrated in the brain in all cases. In 4 of the 22 infected mice there was evidence of rupture of the cyst wall and/or presence of extra-cystic Toxoplasma antigen. Further support for the extra-cystic location of Toxoplasma antigen was obtained by electron microscopy of reprocessed tissue which revealed endozoites in the area immediately surrounding a ruptured cyst. The possible implications of these findings in relation to the pathogenesis of congenital toxoplasmic meningo-encephalitis are discussed.

Toxoplasma gondii: redistribution of monoclonal antibodies on tachyzoites during host cell invasion

Immunodetection of protein P30, a major surface antigen of Toxoplasma gondii tachyzoites, by a specific monoclonal antibody has demonstrated a homogenous distribution of this antigen on the surface of intra- and extracellular tachyzoites at all stages of their endodyogenic development. On living zoites, no redistribution of anti-P30 was obtained, contrasting with the capping obtained with antiserum to T. gondii. Upon invasion of a host cell, however, most of the coat of anti-P30 was shed from preincubated zoites at the level of the moving junction governing the entry of the parasite into the host cell.

Congenital toxoplasmic retinochoroiditis in the mouse--the use of the peroxidase anti-peroxidase method to demonstrate Toxoplasma antigen

The peroxidase anti-peroxidase immunocytochemical staining method has been used to demonstrate Toxoplasma antigen within paraffin-embedded sections of the eyes of mice congenitally infected with Toxoplasma. Intact Toxoplasma tissue cysts were demonstrated within the retina but in no other ocular structure. No endozoites and no extra-cystic antigens were detected by this technique within any of the eyes examined. The possible implications of these findings in relation to the pathogenesis of toxoplasmic retinochoroiditis are discussed.

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.