IL18 and infection: Over the course of a challenge infection with T. circumcincta, transcription of interleukins 1β (IL-1β), 2 (IL-2), 4 (IL-4), 5 (IL-5), 6 (IL-6), 10 (IL-10), 12 (IL-12p40), 13 (IL-13) and 18 (IL-18), interferon gamma (IFNγ), transforming growth factor beta one (TGFβ1) and tumour necrosis factor alpha (TNFα) was examined in the abomasal mucosa and gastric lymph node of naïve and previously infected (PI) yearling sheep and 5-month-old lambs.