Apoptosis as the adaptation mechanism in survival of Trichinella spiralis in the host.

The study evaluates the role of apoptosis-inducing factor (AIF) in the process of striated muscle cell transformation after occupation by Trichinella spiralis. Its relationship with other apoptosis-related factors [apoptotic protease-activating factor 1, Bcl-2 associated protein X (BAX), Bcl-2, caspase 3, survivin, poly (ADP-ribose) polymerase-1 (PARP-1), and endothelial and inducible (iNOS) nitric oxide synthase] was evaluated by immunohistochemistry. In the context of low BAX and caspase 3 expression and strong distribution of AIF in the sarcoplasm and nucleus at the very early stage of infection, we suppose that AIF-mediated signaling is involved in the apoptosis activation in the area of Trichinella occupation. In the time course of nurse cell formation, survivin and caspase 3 migrated into the enlarged nuclei with strong PARP-1 expression. In the end of encapsulation of Trichinella, expression of all proapoptotic factors ceased and only survivin in the nuclei and Bcl-2 positivity in the cytoplasm persisted in the formed nurse cell. The expression of sarcoplasmic iNOS was absent during the process of muscle cell de-differentiation and reappeared within the nurse cell. It seems that upregulation and downregulation of factors of apoptosis in the skeletal muscle cell represents an adaptive mechanism providing a comfortable niche for the parasite.