In vivo depletion of T-cells and cytokines during primary exposure of sheep to parasites

This study examined the role of CD8+ and WC1 + T-cells and of interferon (IFN)-γ in the development of protective immunity against infection with the enteric nematode parasite Trichostrongylus colubriformis in sheep. Monoclonal antibodies (mAb) were administered during induction of the immune response to deplete or neutralise these components. Protection against the primary and challenge infections was assessed by faecal egg count and total worm count. Prolonged administration of mAb recognising IFN-γ and CD8 resulted in significantly increased protection during the 6 week primary infection and following challenge. CD8+ cells were depleted from blood but not from intestinal mucosa. After injection of mAb (CC15) recognising the surface antigen WC1, WC1 + and Tcrγδ+ cells were depleted from blood but not markedly from enteric mucosa, and protection against challenge, although variable, was increased by up to 88%. It appears that CD8+ and WC1 +γδ+ cells and IFN-γ all retard the potential development of naturally acquired immunity against the parasite.