Antigenemia and Specific IgM and IgG Antibody Responses in Rabbits Infected with Toxoplasma gondii

Abstract

Toxoplasmosis is usually diagnosed using serological tests with increases in specific IgG and IgM antibodies. However, these tests are not reliable in immunocompromised patients, nor is it possible to differentiate clearly between the acute and latent forms of toxoplasmosis [1,2]. Because a relatively high percentage of individuals have antibodies without a recognized parasite infection, the early detection of Toxoplasma gondii antigen in the serum or other body fluids of patients would help to diagnose correctly and prevent late complications. For detecting Toxoplasma antigen, several laboratory procedures are available. Direct detection procedures, such as microscopic examination, immune histology, or cell culture are reliable, but they are either insensitive or time-consuming [1,2]. PCR is highly sensitive and specific, although heme, heparin, and other poorly characterized substances have been reported to decrease the efficiency of PCR [3]. ELISA is considered to be a highly sensitive, practical method for detecting the parasite antigen [2]. Many reports have discussed titrating serum antibodies in hosts after Toxoplasma infection, however, little information is available on the correlations among parasitemia, circulating antigens, and antibody titers in T. gondii-infected hosts.To assess the sequential changes in parasite antigen and antibody responses in blood, 5 New Zealand white rabbits weighing 2-3 kg were infected with 1,000 tachyzoites of the RH strain of T. gondii subcutaneously. Then, blood samples were drawn from an ear vein of each rabbit every other day for 20 days. To check parasitemia in the rabbits, 0.5 ml of heparinized blood from each rabbit was injected intraperitoneally into 4 mice, and their survival was monitored for 20 days after infection.The ELISA for detecting circulating antigens was performed in microtitration trays [4,5]. To obtain mouse anti-Toxoplasma antisera, mice were infected with 20 brain cysts of avirulent Me49 strain of T. gondii orally. The mice were then sacrificed at 6 months after infection, and the sera were precipitated with saturated ammonium sulfate solution, resuspended in 0.01 M phosphate buffered saline. Mouse anti-Toxoplasma antisera were diluted with 0.1 M carbonate-bicarbonate buffer (pH 9.6, 10 mg/ml). Then, 100 ml were pipetted into 96-well microtiter plates (Nunc, Roskilde, Denmark) and incubated at 4℃ overnight. The plates were washed with PBS containing 0.05% Tween 20 (PBS/Tween 20), to which 0.1 ml of rabbit serum diluted 1 : 50 with PBS/ Tween 20 containing 0.1% bovine serum albumin was added. Toxoplasma lysate antigen (TLA) was prepared as a control. The plates were incubated at room temperature (RT) for 2 hr, and then 0.1 ml sample serum from the infected rabbit was added. After washing, 150 ml of horseradish peroxidase (HRP)-conju- Antigenemia and Specific IgM and IgG Antibody Responses in Rabbits Infected with Toxoplasma gondiiKorean J Parasitol. Vol. 47, No. 4: 409-412, December 2009 DOI: 10.3347/kjp.2009 Abstract: In this experiment, the correla...

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Prevalence of <i>Toxoplasma gondii</i> Infection in Rabbits of Korea by Serological Tests and Nested Polymerase Chain Reaction

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