Cell mediated and innate immune responses in pigs following vaccination and challenge with Toxoplasma parasites

Toxoplasma gondii has a worldwide distribution and can infect almost all warm blooded animals including pigs and humans. This study aims to examine the immune responses induced in pigs following vaccination (live S48 tachyzoites) and/or challenge with T. gondii oocysts, through the examination of changes in levels of transcription in CD4, CD8α, IFN-γ, IL-12p35, CXCR3, MyD88. The experiment involved four groups of animals; pigs in group 1 (Challenged) (Chal) were challenged orally with (1 × 10³ oocysts) on day 28 of the experiment. Pigs in group 2 (Vaccinated /Challenged) (Vac/Chal) were vaccinated (S48 isolate tachyzoites) on day 0, then challenged on day 28. The group 3 (Vaccinated) (Vac) animals were vaccinated (S48 isolate tachyzoites) on day 0 of the experiment. Finally the group 4 (control) pigs remained non-vaccinated and non-challenged. All animals were culled 6 weeks post challenge. At post mortem samples of retropharyngeal lymph node (RLN), mesenteric LN (MLN) and spleen were collected, RNA was extracted and cDNA synthesised. The results showed significant increases in IFN-γ expression in samples from groups 1 (Chal) and 2 (Vac/Chal) (RLN) and groups 1, 2 and 3 (Vac) (spleen) and in MyD88 expression (RLN) in samples from groups 1, 2 and 3 compared to the group 4 (control) animals. Significant increases were also observed in CD8α expression in group 1 (Chal) (RLN) and groups 1 and 2 (Vac/Chal) (RLN and MLN) compared against group 4 (control) and group 3 (Vac) respectively. Conversely, significant down regulation of CD4 and/or IL-12p35 transcription was found in at least one sample from groups 1 (Chal), 2 (Vac/Chal) and 3 (Vac) compared to group 4 (control) pigs. This study demonstrates that cell mediated and innate immune responses are generated in pigs following exposure to T. gondii parasites (oocysts or tachyzoites), key amongst them appear to be IFN-γ, MyD88 and CD8α.