Antigenemia and specific IgM and IgG antibody responses in rabbits infected with Toxoplasma gondii

Abstract

In this experiment, the correlation between antigenemia and specific antibody responses in Toxoplasma gondii-infected rabbits was assessed. We injected 1,000 T. gondii tachyzoites (RH) subcutaneously into 5 rabbits. Parasitemia, circulating antigens, and IgM and IgG antibody titers in blood were tested by ELISA and immunoblot. For detection of parasitemia, mice were injected with blood from rabbits infected with T. gondii and mice died between days 2 and 10 post-infection (PI). Circulating antigens were detected early on day 2 PI, and the titers increased from day 4 PI and peaked on day 12 PI. Anti-Toxoplasma IgM antibody titers increased on day 6 PI and peaked on days 14-16 PI. IgG was detected from day 10 PI, and the titers increased continuously during the experiment. The antigenic protein patterns differed during the infection period, and the number of bands increased with ongoing infection by the immunoblot analysis. These result indicated that Toxoplasma circulating antigens during acute toxoplasmosis are closely related to the presence of parasites in blood. Also, the circulating antigen levels were closely correlated with IgM titers, but not with IgG titers. Therefore, co-detection of circulating antigens with IgM antibodies may improve the reliability of the diagnosis of acute toxoplasmosis.

Keywords: Toxoplasma gondii; antibody; antigenemia; parasitemia; rabbit.

Fig. 1

Mouse inoculation test for detecting parasitemia in rabbits infected with the RH strain of T. gondii. Four mice of each group were injected with 500 µl of heparinized blood from rabbits intraperitoneally, and mouse survival was monitored for 20 days after the infection.

Fig. 2

Kinetics of the Toxoplasma circulating antigen (●), specific IgM (○), and IgG antibody (▼) titers in T. gondii-infected rabbit sera. The circulating antigen and anti-Toxoplasma IgM and IgG antibody titers were determined by ELISA. Each point represents the mean ± SD of 3 or 5 rabbits.

Fig. 3

Correlation between the circulating antigen and IgM (Line A) or IgG (Line B) antibody titers of sera from rabbits infected with T. gondii. The circulating antigen and antibody titers were determined by ELISA.

Fig. 4

Immunoblot patterns of sera from rabbits infected with 1,000 tachyzoites of the RH strain of T. gondii. Lane 1, molecular weight standard (kDa); lane 2, serum from normal rabbits; lane 3, rabbit serum on day 2 PI; lane 4, day 4 PI; lanes 5 and 6, day 6 PI; lanes 7 and 8, day 8 PI; lanes 9 and 10, day 10 PI; lanes 11 and 12, day 12 PI; lanes 13 and 14, day 14 PI; lanes 15 and 16, day 16 PI; lanes 17 and 18, day 18 PI; lanes 19 and 20, day 20 PI.