Figure 4.

Immunization schedule and humoral immune response induced by vaccination. (A) Schematic diagram of the immunization protocol. BALB/c mice (23 mice/group) were immunized subcutaneously with 50 μg of the recombinant proteins (HBc_Δ, H82, HBc_ΔH82, H301, HBc_ΔH301, R82, HBc_ΔR82, R301, and HBc_ΔR301) at 0,2, and 4 weeks after first immunization. Serum samples were collected at 0, 2, 4, and 6 weeks. Three mice per group were sacrificed and spleens were obtained 2 weeks after the last immunization. Then, 10 mice per group were infected intraperitoneally with 1 × 10³ tachyzoites of the RH strain, and the other 10 mice in each group were orally challenged with 30 cysts of the Pru strain. (B) Detection of the levels of T. gondii-specific IgG antibody (a) and IgG1 and IgG2a subclass antibodies (b) in the sera of the immunized mice by enzyme-linked immunosorbent assay (ELISA). Serum samples were collected from the mice by retro-orbital bleeding at 0, 2, 4, and 6 weeks after the first immunization. After stimulation with 10 μg/ml of the recombinant proteins, humoral immune responses were analyzed. Results have been expressed as the mean of OD₄₅₀ ± SD values (n = 15) and are representative of at least three independent experiments. *p < 0.05, **p < 0.01, ***p < 0.001.