An investigation of the antigenic structure of Toxoplasma gondii

Cytokine responses induced by Toxoplasma gondii in astrocytes and microglial cells

To investigate the role of astroglia in intracerebral immune response to Toxoplasma gondii, astrocytes cultured from mouse brain were inoculated with mouse-virulent or -avirulent toxoplasma strains. In comparison to microglia/ brain macrophages, astrocytes as host cells allowed stronger proliferation of avirulent parasites. Toxoplasma infection of astroglia was accompanied by release of interleukin- (IL)1 alpha, IL-6, and granulocyte/macrophage colony-stimulating factor (GM-CSF) activity, whereas alternative challenge by lipopolysaccharide (LPS) evoked no IL-1 response and significantly higher titers of IL-6 and GM-CSF. At the mRNA level, both stimuli induced transcription of all three cytokines in astrocytes. Secretion of IL-1 and IL-6 upon infection was triggered by T. gondii brady- and tachyzoites in a time- and dose-dependent manner. Heat killing of parasites, but not an exposure to polymyxin B, abrogated their cytokine-inducing activity, thus indicating that an LPS-independent stimulus is provided by T. gondii. When administered in combination, LPS synergistically augmented the IL-1-inducing effect of toxoplasma infection. In comparison, T. gondii-induced, but not an LPS-triggered, IL-6 response of astrocytes resisted to antagonization with IL-10. The IL-6 response of parasitized astroglia was up-regulated by external tumor necrosis factor (TNF)-alpha and transforming growth factor (TGF)-beta 1, with only TNF-alpha enhancing simultaneous release of IL-1. Substantial secretion of IL-10 and TNF-alpha was detected in T. gondii-infected microglia, but not in astrocyte cultures. A possibly autocrine stimulation of infected astroglia via IL-1 was found to be unlikely, since addition of IL-1 receptor antagonist did not affect the release of IL-6 and GM-CSF while inhibiting these responses in IL-1-treated cells. The findings substantiate a separate, T. gondii-induced pathway of astroglia activation characterized by the release of IL-1 which may drive local inflammatory reaction both at initial infection of the brain and during reactivating toxoplasmosis.

Identification of Toxoplasma gondii antigens involved in the IgM and IgG indirect hemagglutination tests for the diagnosis of toxoplasmosis

Crude Toxoplasma gondii antigens represent raw material used to prepare reagents to be employed in different serologic tests for the diagnosis of toxoplasmosis, including the IgM and IgG indirect hemagglutination (IgG-HA and IgM-HA) tests. So far, the actual antigenic molecules of the parasite involved in the interaction with agglutinating anti-T. gondii antibodies in these tests are unknown. The absorption process of serum samples from toxoplasmosis patients with the IgG-HA reagent (G-toxo-HA) demonstrated that red cells from this reagent were coated with T. gondii antigens with Mr of 39, 35, 30, 27, 22 and 14 kDa. The immune-absorption process with the IgM-HA reagent (M-toxo-HA), in turn, provided antibody eluates which recognized antigenic bands of the parasite corresponding to Mr of 54, 35 and 30 kDa, implying that these antigens are coating red cells from this reagent. The identification of most relevant antigens for each type of HA reagent seems to be useful for the inspection of the raw antigenic material, as well as of reagent batches routinely produced. Moreover the present findings can be used to modify these reagents in order to improve the performance of HA tests for the diagnosis of toxoplasmosis.

Effect of feline immunodeficiency virus infection on Toxoplasma gondii-specific humoral and cell-mediated immune responses of cats with serologic evidence of toxoplasmosis

Serum samples from 89 cats with serologic evidence of toxoplasmosis were identified by using an enzyme-linked immunosorbent assay (ELISA) that detected Toxoplasma gondii-specific immunoglobulin M (IgM) or T. gondii-specific immunoglobulin G (IgG). Concurrent feline immunodeficiency virus (FIV) infection was detected in 36 cats using an ELISA for detection of FIV-specific IgG. The majority of the cats in both the FIV-seropositive and FIV-seronegative groups were male and > 5 years of age. FIV-seropositive cats were more likely to have T. gondii IgM titers without IgG (P < 0.05) or any T. gondii IgM titer (P < 0.05) than were FIV-seronegative cats. FIV-seronegative cats (1328) had a higher T. gondii IgG geometric mean titer than did FIV-seropositive cats (724) and were more likely to have T. gondii IgG titers > 1:2048 than were FIV-seropositive cats (P < 0.05). Cats with serologic evidence of both T. gondii and FIV infections had persistent T. gondii IgM titers for > 12 weeks. Lymphoblast transformation in response to concanavalin A, T. gondii-specific intracellular antigens, and T. gondii-specific secretory antigens was compared in T. gondii seropositive and FIV-seronegative cats, cats with serologic evidence of T. gondii infection alone, and cats with serologic evidence of concurrent FIV and T. gondii infections. Lymphocytes from all but one cat in the FIV-seropositive group responded to concanavalin A. Whereas lymphocytes from FIV-seronegative cats with serologic evidence of toxoplasmosis responded to T. gondii-specific antigens, four of five of the FIV-seropositive cats with concurrent serologic evidence of toxoplasmosis did not.

Human glioblastoma cell line 86HG39 activates T cells in an antigen specific major histocompatibility complex class II-dependent manner

The capacity of three different human glioblastoma cell lines to activate human T cells was analysed by measuring major histocompatibility complex (MHC) antigen expression, monokine secretion and lectin, mAb OKT3 and antigen-driven T cell proliferation. All glioblastoma cells tested were able to induce PHA and concanavalin A (ConA)-driven T cell proliferation in a dose-dependent fashion, while all failed to induce T cell activation with mAb OKT3. In addition, the glioblastoma cell line 86HG39 was able to induce tetanus toxoid and toxoplasma lysate antigen-specific T cell proliferation. The responding T cell lines originated from only one out of five different donors. This foreign antigen-specific T cell proliferation induced by 86HG39 cells could be inhibited with mAb L243 directed against HLA-DR molecules. The study of monokine secretion by 86HG39 cells showed a strong interleukin (IL)-6 secretion after lipopolysaccharide (LPS) treatment, whilst no IL-1 secretion was observed. Furthermore, only 86HG39 cells were positive for HLA-DR molecules, whereas interferon (IFN) gamma treatment of 87HG28 and 87HG31 cells was necessary for the induction of class II antigen expression. Thus, cell line 86HG39 shows many features of an antigen presenting cell and the interaction of these cells with MHC compatible human T cells might be a useful model to study cellular immune reactions within the central nervous system.

Detection and characterization of circulating antigens in acute experimental infections of mice with four different strains of Toxoplasma gondii

Acute infections with four different strains of Toxoplasma gondii, all of them being highly pathogenic for mice, were provoked by intraperitoneal injection of 2.2 x 10(7) trophozoites. The times of the appearance of circulating antigens in the sera of the infected mice were determined and the amounts of these antigens were measured by an enzyme-linked immunosorbent assay. The molecular weight of the circulating antigens was determined by gel filtration and by Western blot following PAGE. The isoelectric points of these antigens were determined by immunoblotting after isoelectric focusing. Circulating antigens were detectable up to ng amounts/ml serum from the 1st day p.i. onwards. The circulating antigens consisted of a number of proteins with molecular weights of greater than 10(4), 300, 65, 25, and less than 5 kd. The isoelectric points of these proteins were situated between pH 3.5 and pH 7. Time of appearance and structure of the circulating antigens were very similar in all four Toxoplasma strains. Circulating antigens are apparently generated regularly in experimental acute Toxoplasma infections, and lysis of parasite cells appears to be the major mechanism of their formation.

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.

Use of monoclonal antibodies in an ELISA to detect IgM class antibodies specific for Toxoplasma gondii

Two monoclonal antibodies CH6 and C1E3 were used in an antibody class capture assay for the detection of IgM antibodies specific for Toxoplasma gondii. CH6 was used on the solid phase to capture human IgM. After a Toxoplasma gondii antigen had been added, specifically bound material was detected using C1E3 coupled to horseradish peroxidase. The assay was compared with an established system using polyclonal antisera at both the capture and antigen detection stages. A good correlation was found, with 97.3% (125 of 128) of sera giving the same classification in both assays. Three sera were positive only in the polyclonal system. No false positive results were found when 118 negative sera were examined. The two monoclonal antibodies provide a viable alternative to the use of polyclonal sera at the capture and antigen detection stages in the antibody class capture assay for the measurement of specific IgM against T gondii.

Experimental studies on circulating antigen of Toxoplasma gondii in intermediate hosts: criteria for detection and structural properties

The present study was performed to demonstrate circulating antigen (cag) of Toxoplasma gondii in the sera of orally and intraperitoneally infected rabbits and swine, to determine the time of their appearance after infection, and to characterize the antigenic components of the cag by means of affinity chromatography, SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and electrophoretic blot onto nitrocellulose sheets. Cag, as detected by an indirect ELISA, was found in the sera of both rabbits and swine from week 5 to week 8 after infection. Electrophoretic separation of cag extracted from swine and human sera showed 5 and 8 distinct protein bands, respectively, the molecular weight of which ranged between 25 and 100 kD. After Western blot, 2 of the 5 protein bands of swine-cag (27 and 57 kD) and 3 of the 8 protein bands of human cag (27, 32, and 57 kD) reacted with the anti-Toxoplasma antibody used in the ELISA. On the basis of the data presented, the influence of the dose and mode of infection as well as that of the preparation method of antisera on cag detection is 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.

Enzyme linked immunosorbent assay for detection of antibodies against Besnoitia besnoiti in cattle

The use of the ELISA method for the detection of antibodies to B. besnoiti in cattle is described and compared to the IFAT technique. One hundred and twenty-one sera were examined, of which 61 were sera of calves experimentally infected with B. besnoiti, 52 sera from field animals and eight were sera with high titres of antibodies to other parasites. The specificity of both assays correlates but ELISA seemed to be more sensitive. The ELISA technique provides a rapid and reliable method for the screening of B. besnoiti infection in cattle.

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.

Characterization of Toxoplasma gondii antigens that react with human immunoglobulin M and immunoglobulin G antibodies

Studies were performed to define the nature of the Toxoplasma gondii antigens that are recognized by human immunoglobulin M (IgM) and IgG antibodies. Both IgM and IgG antibodies were found to be directed mainly against T. gondii membrane antigens in sera obtained from patients with acute toxoplasmosis. Treatment of the membrane preparation with DNase, RNase, or lipase had no apparent effect on the reactivity of the membrane antigens with IgM and IgG antibodies. Lipids isolated from tachyzoites were not recognized by either IgM or IgG antibodies. Exposure of T. gondii membranes to heat, proteolysis, or oxidation with sodium periodate decreased the reactivity of the membrane preparations with both IgM and IgG antibodies. A preparation of T. gondii proteins and polysaccharides were recognized by both immunoglobulin classes. T. gondii polysaccharides reacted with human IgG antibodies produced during both the acute and chronic phases of the infection. We concluded that, after infection with T. gondii, IgM and IgG antibodies are elicited in response to both protein and carbohydrate constituents of the invading parasite.

Comparative study of three tests (dye test, indirect haemagglutination test, latex agglutination test) for the detection of antibodies to Toxoplasma gondii in human sera

An evaluation has been made of a commercial latex agglutination test, Toxotest-MT (TMT) (Eiken, Japan), for the detection of antibodies to Toxoplasma gondii in human sera. In qualitative studies, 878 sera were examined in both the TMT and dye test (DT) and 96.6% agreement was found, In quantitative studies 339 sera were titrated in the TMT and DT, with 337 of these sera also titrated in the indirect haemagglutination test (IHAT). Agreement between the DT and TMT was best, 78% of the sera showing titres within +/- 1 dilution in the two tests. The IHAT and TMT gave 66% agreement, while the DT and IHAT showed least agreement, 40.9%. The results suggest that the pattern of antigenic determinants to which antibody levels are measured are different in the three test systems. The TMT is a better substitute for the DT than the IHAT.