Quantitation of antibodies to Toxoplasma gondii in swine sera by enzyme-linked immunosorbent assay

Naturally occurring antibodies that react with protozoan parasites

In this paper, Eiji Konishi reviews general features of naturally occurring (natural) antibodies that react with protozoan parasites. Several functions of natural antibodies have been identified in relation to their multireactivity, but reports on protozoan infection have dealt mainly with the role of natural antibodies in the innate immunity of the host, These antibodies lyse cells in the presence of complement and have opsonizing activity, in vitro. Studies of their origin have shown the possibilities of (1) continuous polyclonal stimulation by gastrointestinal bacteria, and (2) there being multireactive antibodies secreted by CD5(+) B cells. The protective functions of natural antibodies are important in the interpretation of the host range, the mode of infection, and the course of the disease of certain protozoan parasites.

Correlation between antibody levels in Toxoplasma gondii infected pigs and pathogenicity of the isolated parasite

Sera and diaphragm muscle tissues were obtained from 109 commercial pigs between September 1991 and May 1992 from the slaughterhouse at La Plata, Provincia Buenos Aires, Argentina. Anti-Toxoplasma gondii IgG antibody reactivity to T. gondii antigens were assayed using sera by indirect immunofluorescence assay and immunoblotting technique. Anti-T. gondii IgG titers at serum dilutions of 1:1024 and higher were noted in 11.0% of the tested sera, and at dilutions of 1:16 and lower in 36.7% of the serum samples. Using mouse inoculation test, T. gondii was isolated from 14 pig diaphragm samples. Of five samples derived from pigs with antibodies at dilutions of 1:1024 and higher, four contained trophozoites which, when inoculated into mice intraperitoneally, killed all recipient hosts within 15 days post inoculation. Parasites detected in seven out of eight samples from pigs with antibodies at serum dilutions of 1:64 and lower formed cysts in the brain, and mice survived longer than 13 days post inoculation. Immunoblotting demonstrated antibody reactivity in pig sera samples with relatively high titers for parasite antigens. Results of the present study suggest that antibody production in infected pigs is apparently dependent on the pathogenicity of the parasite strain.

ELISA for assessing Toxoplasma gondii antibodies in pigs

The ELISA technique was applied to assess Toxoplasma gondii antibodies in pigs. Among 925 swine examined 36.4 per cent of the animals were seropositive. Serum titres ranged from 100 to 3,200.

Naturally occurring immunoglobulin M antibodies to Toxoplasma gondii in Japanese populations

Varying degrees of naturally occurring immunoglobulin (Ig) M antibodies to Toxoplasma gondii were observed in almost all of adult Japanese populations negative for IgG antibodies as determined by an enzyme-linked immunosorbent assay (ELISA). The antibody activity was reduced by absorption of sera with Toxoplasma soluble antigen or by 2-mercaptoethanol treatment of the IgM fraction after sucrose density gradient centrifugation. Umbilical cord sera had almost no detectable IgM antibodies, and the ELISA value in infants increased with age until 1 year. Most paired sera collected from adults at a 1-year interval showed constant IgM antibody levels, suggesting retention of natural IgM antibodies throughout their lives without changing ELISA values of greater than or equal to 0.1/year. Polar staining was observed in immunofluorescent studies for 14 serum samples with natural IgM antibody levels of greater than or equal to 0.5, while samples obtained from a pregnant woman with natural IgM antibody levels of greater than or equal to 0.9 reacted to the whole organism as was observed in positive sera of acute patients. Western blotting analysis revealed that natural IgM antibodies were directed to multiple antigen molecules. The band pattern differed slightly from one serum to another, but almost consistent patterns were observed in sera sequentially obtained from an adult over 4 years.

Annual change in immunoglobulin G and M antibody levels to Toxoplasma gondii in human sera

Sera collected from a Japanese population over 4 years at yearly intervals were examined for antibodies to Toxoplasma gondii by enzyme-linked immunosorbent assay (ELISA). Distributions of immunoglobulin (Ig) G antibody levels for 6 age groups consistently showed two antibody groups with constant mean ELISA values. Quantitative analysis of annual changes in IgG antibody levels for 1,366 pairs indicated increase of greater than or equal to 0.1 in 28 samples and decrease of greater than or equal to 0.1 in 58 samples, with the remaining 1,280 samples showing changes of less than 0.1. Mean ELISA values of samples with increase and decrease were 0.479 and 0.833, respectively, and the difference of 0.354 was similar to 0.412, that was the sum total of mean annual changes in samples with increase (0.228) and decrease (0.184). Increase of greater than or equal to 0.1 from the initial IgG antibody level of less than 0.1, which was considered as a serological evidence for newly acquired infection, was observed in 3 samples, but no increase was demonstrated in IgM antibody level. The changing pattern of IgG and IgM antibody levels in people during the initial and chronic phases of asymptomatic infections is discussed.

A pregnant woman with a high level of naturally occurring immunoglobulin M antibodies to Toxoplasma gondii

A pregnant woman diagnosed as positive for immunoglobulin M antibodies to Toxoplasma gondii did not have a subsequent rise of specific immunoglobulin G antibodies until delivery. The antibodies were therefore considered as naturally occurring immunoglobulin M antibodies. The baby was completely normal without any clinical and serologic signs suggestive of congenital toxoplasmosis.