Toxoplasma gondii KI-1, a recent new isolate from Korea, shows similar pathogenicity and infectivity to mice compared to the virulent RH strain. To understand characteristics of host immunity, including immune enhancement or suppression, we investigated proliferative responses and phenotypes of spleen cells. In addition, kinetics of IFN-gamma, a Th1 cytokine, was examined in BALB/c mice up to day 6 post-infection (PI). Intraperitoneal injection of mice with 103 KI-1 tachyzoites induced significant decreases (P < 0.05) in proliferative responses of spleen cells. This occurred at days 2-6 PI even when concanavalin A (con A) was added and when stimulated with KI-1 antigen, suggesting suppression of the immunity. CD4+ T-cells decreased markedly at day 2 PI (P < 0.05), whereas CD8+ T-cells, NK cells, and macrophages did not show significant changes, except a slight, but significant, increase of CD8+ T-cells at day 6 PI. The capacity of splenocytes to produce IFN-gamma by con A stimulation dropped significantly at days 2-6 PI. These results demonstrate that intraperitoneal injection of KI-1 tachyzoites can induce immunosuppression during the early stage of infection, as revealed by the decrease of CD4+ T-cells and IFN-gamma.
Animals ; CD4-Positive T-Lymphocytes/*immunology ; CD8-Positive T-Lymphocytes/immunology ; Cell Proliferation ; Female ; *Immune Tolerance ; Interferon-gamma/secretion ; Killer Cells, Natural/immunology ; Macrophages/immunology ; Mice ; Mice, Inbred BALB C ; Spleen/*immunology ; Toxoplasma/*immunology/*pathogenicity

This study investigated whether elevated host immune capacity can inhibit T. gondii infection. For this purpose, we used silk protein extracted from Bombyx mori cocoons as a natural supplement to augment immune capacity. After silk protein administration to BALB/c mice for 6 weeks, ratios of T lymphocytes (CD4+ and CD8+ T-cells) and splenocyte proliferative capacities in response to Con A or T. gondii lysate antigen (TLA) were increased. Of various cytokines, which regulate immune systems, Th1 cytokines, such as IFN-gamma, IL-2, and IL-12, were obviously increased in splenocyte primary cell cultures. Furthermore, the survival of T. gondii (RH strain)-infected mice increased from 2 days to 5 or more days. In a state of immunosuppression induced by methylprednisolone acetate, silk protein-administered mice were resistant to reduction in T-lymphocyte (CD4+ and CD8+ T-cells) numbers and the splenocyte proliferative capacity induced by Con A or TLA with a statistical significance. Taken together, our results suggest that silk protein augments immune capacity in mice and the increased cellular immunity by silk protein administration increases host protection against acute T. gondii infection.
Animals ; Bombyx/*chemistry ; CD4-CD8 Ratio ; Cell Proliferation ; Cells, Cultured ; Cytokines/secretion ; Insect Proteins/*immunology ; Leukocytes, Mononuclear/immunology ; Male ; Mice ; Mice, Inbred BALB C ; Silk/immunology ; Spleen/immunology ; Survival Analysis ; Toxoplasma/*immunology/pathogenicity ; Toxoplasmosis, Animal/immunology/*prevention & control

Toxoplasma gondii Korean isolate (KI-1) tachyzoites were inoculated intraduodenally to BALB/c mice using a silicon tube, and the course of infection and immune responses of mice were studied. Whereas control mice, that were infected intraperitoneally, died within day 7 post-infection (PI), the intraduodenally infected mice survived until day 9 PI (infection with 1x10(5) tachyzoites) or day 11 PI (with 1x10(6) tachyzoites). Based on histopathologic (Giemsa stain) and PCR (B1 gene) studies, it was suggested that tachyzoites, after entering the small intestine, invaded into endothelial cells, divided there, and propagated to other organs. PCR appeared to be more sensitive than histopathology to detect infected organs and tissues. The organisms spread over multiple organs by day 6 PI. However, proliferative responses of splenocytes and mesenteric lymph node (MLN) cells in response to con A or Toxoplasma lysate antigen decreased significantly, suggesting immunosuppression. Splenic CD4+ and CD8+ T-lymphocytes showed decreases in number until day 9 PI, whereas IFN-gamma and IL-10 decreased slightly at day 6 PI and returned to normal levels by day 9 PI. No TNF-alpha was detected throughout the experimental period. The results showed that intraduodenal infection with KI-1 tachyzoites was successful but did not elicit significant mucosal immunity in mice and allowed dissemination of T. gondii organisms to systemic organs. The immunosuppression of mice included reduced lymphoproliferative responses to splenocytes and MLN cells to mitogen and low production of cytokines, such as IFN-gamma, TNF-alpha, and IL-10, in response to T. gondii infection.
Animals ; Cell Proliferation ; Cytokines/secretion ; Disease Models, Animal ; Duodenum/immunology/parasitology/pathology ; Endothelial Cells/parasitology ; Histocytochemistry ; Immune Tolerance ; Lymph Nodes/immunology ; Mice ; Mice, Inbred BALB C ; Polymerase Chain Reaction ; Rodent Diseases/immunology/parasitology/pathology ; T-Lymphocyte Subsets/immunology ; Toxoplasma/*immunology/pathogenicity ; Toxoplasmosis, Animal/*immunology/parasitology/pathology

Although some reports have been published on the protective effect of antibodies to Toxoplasma gondii surface membrane proteins, few address the inhibitory activity of antibodies to dense granular proteins (GRA proteins). Therefore, we performed a series of experiments to evaluate the inhibitory effects of monoclonal antibodies (mAbs) to GRA proteins (GRA2, 28 kDa; GRA6, 32 kDa) and surface membrane protein (SAG1, 30 kDa) on the invasion of T. gondii tachyzoites. Passive immunization of mice with one of three mAbs following challenge with a lethal dose of tachyzoites significantly increased survival compared with results for mice treated with control ascites. The survival times of mice challenged with tachyzoites pretreated with anti-GRA6 or anti-SAG1 mAb were significantly increased. Mice that received tachyzoites pretreated with both mAb and complement had longer survival times than those that received tachyzoites pretreated with mAb alone. Invasion of tachyzoites into fibroblasts and macrophages was significantly inhibited in the anti-GRA2, anti-GRA6 or anti-SAG1 mAb pretreated group. Pretreatment with mAb and complement inhibited invasion of tachyzoites in both fibroblasts and macrophages. These results suggest that specific antibodies to dense-granule molecules may be useful for controlling infection with T. gondii.
Animals ; Antibodies, Monoclonal/*pharmacology/therapeutic use ; *Antigens, Protozoan ; Female ; Fibroblasts/parasitology ; Host-Parasite Relations ; Immunization, Passive ; Macrophages/parasitology ; Mice ; Mice, Inbred BALB C ; Protozoan Proteins/*immunology ; Support, Non-U.S. Gov't ; Toxoplasma/*pathogenicity ; Toxoplasmosis/parasitology/*therapy