Immunoprotective responses against murine sarcocystosis by β - Irradiated sporocysts

This study aimed to induce protective immunity against infection with Sarcocystis muris in experimental mice using β-irradiated sporocysts. Mice were vaccinated with 50 sporocysts of S. muris which were exposed to 1.84 μSv β-irradiation for 2, 4 and 8 h. After challenge infection, different samples were taken for evaluation. Serum and intestinal wash were assayed for IFN-γ and IgA, respectively. Mesenteric lymph nodes (MLNs) and spleen were investigated for CD4⁺ and CD8⁺ T cells using immunohistochemistry. For liver, the morphological changes in parasitic stages and the count of infiltrated CD8⁺ T, NK1.1⁺ and FasL⁺ cells were also investigated. Real time (RT) - PCR was used for detection of liver MHC I, CD1d, IFN-γ, perforin and FasL as well as the parasite 18S ribosomal(r) RNA in liver and muscle tissues. Alterations of liver parasitic stages as well as a decrease in the infection with the parasite in both of liver and muscle tissues were dependent on radiation exposure time. An investigation for the mechanism of immunoprotection showed an increase in liver NK1.1⁺ & FasL⁺ cells, serum IFN-γ and intestinal IgA, while CD4⁺ and CD8⁺ T showed a remarkable increase in MLNs and spleen. FasL expression increased in the liver dependently on radiation exposure time, while perforin, MHC I and CD1d were not. β-irradiated sporocysts with 1.84 μSv for 8 h s could induce the highest protection against infection with Sarcocystis. This could be largely relied on the increased infiltration of NK cells and associated higher expression of FasL in the liver.