An assessment of a commerically available haemagglutination test for detecting toxoplasma antibodies in ovine sera

Toxoplasma infection and systemic lupus erythematosus: analysis of the serological response by immunoblotting

AIMS

To examine the serological response of patients with systemic lupus erythematosus (SLE) and toxoplasma infection and to compare the blot profiles with those from immunocompetent subjects of similar immune response.

METHODS

Forty serum samples from patients with SLE were tested for toxoplasma antibodies using the dye and indirect haemagglutination tests. Specific IgM was measured by mu-capture enzyme linked immunosorbent assay (ELISA). The sera were immunoblotted using antigen strips prepared from the RH strain of Toxoplasma gondii. For comparison, control blots were prepared from pooled sera from immunocompetent subjects with serological evidence of acute (pool 1), or chronic (pool 2) toxoplasma infection, or with no evidence of infection (pool 3).

RESULTS

Some of the blot profiles from the patients with SLE were compatible with the corresponding serology but others showed considerable variation, particularly among the IgM blots. The blots from sera with low dye test titres suggested that the latter could be false positive results.

CONCLUSIONS

Toxoplasma infection may enhance the production of autoantibodies which, when combined with the high titres characteristic of SLE, might interfere in the dye test and other serological tests. Immunoblotting could prove useful in the immunocompromised for confirming the presence of specific toxoplasma antibodies and for the staging of infection in those with positive serology.

Toxoplasmosis in heart and heart and lung transplant recipients

Of the first 250 heart and 35 heart and lung transplant recipients at Papworth Hospital, Cambridge, who survived for more than one month after transplantation, 217 heart and 33 heart and lung patients were investigated serologically for evidence of Toxoplasma gondii infection. Six patients acquired primary T gondii infection, most probably from the donor organ. Five patients experienced T gondii recrudescence, two of whom had recovered from primary infection a few years earlier. Two patients died from primary T gondii infection and the severity of symptoms in the other patients with primary infection was related to the amount of immunosuppressive treatment. Prophylaxis with pyrimethamine (25 mg a day for six weeks) was introduced for T gondii antibody negative transplant recipients who received a heart from a T gondii antibody positive donor after the first four cases of primary toxoplasmosis. Of the seven patients not given pyrimethamine, four (57%) acquired primary T gondii infection. This compared with two of the 14 patients (14%) given prophylaxis.

Serological survey for Toxoplasma infections in sheep

A factorial-design survey was performed to determine the prevalence of specific antibody against Toxoplasma in young and adult sheep from 6 areas in 3 different geoclimatic zones in South Australia. Serum samples obtained from 1,159 sheep belonging to 59 flocks were tested by a conventional indirect haemagglutination test (IHAT) as well as by an enzyme-linked immunosorbent assay (ELISA) which used class-specific conjugates to detect both IgG and IgM against Toxoplasma. Titres greater than 64 were detected in 7.4%, 9.2% and 25.2% of the sheep by the IHAT, IgG-ELISA and IgM-ELISA respectively. A significant positive correlation was found between the results of the IgG-ELISA and the IHAT with identical results obtained for 1,050 samples. Antibody detected by all 3 tests was more prevalent and higher in titre in adult sheep than in lambs as well as in sheep from Kangaroo Island than in those from mainland South Australia. Although the regional differences in prevalence suggested a relationship with climate, no significant correlations were detected between the prevalence results and any single climatic factor; namely, average annual rainfall, average annual evaporation or mean temperature range.

Problems with serological diagnosis of Toxoplasma gondii infections in heart transplant recipients

Of the first 128 patients to receive either heart or heart and lung transplants at Papworth Hospital, four developed Toxoplasma gondii infections acquired from the donor heart and two died. Six patients had passively acquired T gondii antibody as a result of blood transfusions around the time of transplantation. Eight patients developed antibodies against T gondii, which were detectable by changes in the latex agglutination test titres but not by those of the dye test. These false positive latex agglutination reactions occurred simultaneously with cytomegalovirus infection and were associated with the IgM serum fraction in the patients' sera. These reactions were not associated with cytomegalovirus specific IgM, Paul-Bunnell antibody, nor detectable rheumatoid factor. These findings emphasise the need for T gondii dye test confirmation of latex agglutination test titre rises in heart transplant recipients.

Detection of specific IgG and IgM antibodies to Toxoplasma gondii with a commercially available enzyme immunoassay kit system

A total of 138 serum samples submitted for toxoplasma serology have been examined by enzyme immunoassay using kits produced by Labsystems Oy for the detection of specific antibodies of the IgG and IgM class. Results were compared with the dye test, an indirect haemagglutination test, and an indirect immunofluorescence test for specific IgM. The enzyme immunoassay was less sensitive than the dye test, but by running both IgG and IgM enzyme immunoassays, 92.4% sensitivity was achieved. The specificity of the enzyme immunoassay was good, with only one dye test negative serum giving a positive (but weak) IgG enzyme immunoassay reaction. Thirty serum samples from patients with no evidence of exposure to Toxoplasma gondii gave negative results in the IgM enzyme immunoassay. Enzyme immunoassay results were expressed in enzyme immunoassay units, as a percentage value of a standard serum. This convention will be of value in the direct comparison of assay systems and in the application of quality control procedures.

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.