Cytotoxic cells of the immune system may kill infected or transformed host cells via the perforin/granzyme or the Fas ligand (FasL) pathways. The purpose of this study was to determine mRNA expression of perforin, granzyme A and FasL inEimeria tenella-infected tissues at primary infection and infection of immune chickens as an indirect measure of cytotoxic cell activity. Chickens were rendered immune by repeated E. tenellainfections, which were manifested as an absence of clinical signs or pathological lesions and significantly reduced oocyst production upon challenge infection. During primaryE. tenellainfection, perforin, granzyme A and FasL mRNA expression in caecal tissue was significantly increased at 10 days after infection, compared to uninfected birds. In contrast, at infection of immune birds, perforin and granzyme A mRNA expression in caecal tissue was significantly increased during the early stages of E. tenellachallenge infection, days 1–4, which coincided with a substantial reduction of parasite replication in these birds. These results indicate the activation of cytotoxic pathways in immune birds and support a role for cytotoxic T cells in the protection againstEimeriainfections.
