In vitro model of postoncosphere development, and in vivo infection abilities of Taenia solium and Taenia saginata

Abstract

Taenia solium is known to cause human cysticercosis while T. saginata does not. Comparative in vitro and in vivo studies on the oncosphere and the postoncospheral (PO) forms of T. solium and T. saginata may help to elucidate why cysticercosis can occur from one and not the other. The aim of this study was to use in vitro culture assays and in vivo models to study the differences in the development of the T. solium and T. saginata oncosphere. Furthermore, this study aimed to evaluate the expression of cytokines and metalloproteinases (MMPs) in human peripheral blood mononuclear cells (PBMCs), which were stimulated by these oncospheres and PO antigens. T. solium and T. saginata activated oncospheres (AO) were cultured in INT-407 and HCT-8 intestinal cells for 180 days. The T. solium began to die while the T. saginata grew for 180 days and developed to cysticerci in INT-407 cells. Rats were inoculated intracranially with AO and PO forms of either T. saginata or T. solium. Rats infected with T. solium AO and PO forms developed neurocysticercosis (NCC), while those infected with the T. saginata did not. Human PMBCs were stimulated with antigens of AO and PO forms of both species, and the production of cytokines and metalloproteinases (MMPs) was measured. The T. solium AO antigen stimulated a higher production of IL-4, IL-5, IL-13, IFN-γ, and IL-2 cytokines compared to T. saginata AO. In the PO form, the T. saginata PO antigen increased the production of IL-4, IL-5, IL-13, IFN-γ, IL-1β, IL-6, IL-10, TNF-α and IL-12 cytokines compared to T. solium, suggesting that this global immune response stimulated by different forms could permit survival or destruction of the parasite depending of their life-cycle stage. Regarding MMPs, T. solium AO antigen stimulated a higher production of MMP-9 compared to T. saginata AO antigen, which may be responsible for altering the permeability of intestinal cells and facilitating breakdown of the blood-brain barrier during the process of invasion of host tissue.

Fig 1. Light microscopy of postoncospheral form of T. solium and T. saginata displaying parasite morphology at different times of development in INT-407 culture.

T. solium and T. saginata at 15-day PO form (a) 30-day PO form (b) and at 60-day PO form (c) Magnification 100x.

Fig 2. Light microphotography of T. saginata postoncospheral form at 120 and 180 days of culture in INT-407 cells.

At 120 days of culture a pre-scolex-like structure appears (a) and at 180 days of culture, a scolex appears (b). Magnification 100x.

Fig 3. Production of cytokines by human PBMCs stimulated with T. solium and T. saginata AO form.

Cultures supernatant were collected at 48 h from healthy human PBMC stimulated with 20 μg/ml of activated oncosphere antigens. (a) T_H1- related cytokines, (b) T_H2- related cytokines, and (c) other cytokines. Data presented are the mean ± SEM of healthy human donors (n = 10–13) minus control. * P< 0.05 was considered statistically significant.

Fig 4. Production of cytokines by human PBMCs stimulated by T. solium and T. saginata PO 30-day forms.

Cultures supernatant were collected at 48 h from healthy human PBMC stimulated with 20 μg/ml of 30-day PO form antigens. (a) T_H1- related cytokines and (b) T_H2- related cytokines, and (c) other cytokines. Data presented are the mean ± SEM of healthy human donors (n = 10–13) minus control. * P< 0.05 was considered statistically significant.

Fig 5. Production of MMP-9 by human PBMC stimulated with T. solium and T. saginata form.

Culture supernatant was collected at 48 h from healthy human PBMC stimulated with 20 μg/ml of activated oncosphere antigens and 20 μg/ml of 30-day PO form antigens of T. solium and T. saginata. Data presented are the mean ± SEM of healthy human donors (n = 5–6) minus control. * P< 0.05 was considered statistically significant; n.s. = not significant.