i., and 22·1 times higher on day 31 p.i. Perhaps unexpectedly, Group 5 hamsters (primary + secondary infections) made a slower start, with eosinophil numbers just 9·4 times higher 10 days p.c., but caught up rapidly and by day 17 p.c. eosinophil counts were 27·7 times higher than those BMN 673 in naïve animals on day 10 (day 73 of the experiment), before falling by days 24 and 31 p.c. This curve was best described by the quadratic equation y = −437·9 +87·1x−1·95×2 (where y = eosinophils/mm2 and x = days after challenge); R2 = 41·3%, F2,15 = 5·3, P = 0·019). In naïve hamsters, Paneth cell numbers average 1–3 cells per crypt (18), and here the values in naive animals were well within

the normal range (Figure 6). As found earlier, (18) the mean numbers in animals experiencing a primary infection were lower

(Figure 6, days 73 and 94 p.i. in Group 2, primary continuous infection). When hamsters were given the second infection alone (Group 4), Paneth cell numbers were in the naive control range on day 10 p.i., but already lower by day 31 p.i. Removal of the adult worm population in Group 3 (primary abbreviated infection), caused an exaggerated response (Figure 6), with mean numbers more than doubling on days 73 and 94 p.i. (actually 38 and 59 days selleck chemicals llc after removal of adult worms, see Table 1). Immunized-challenged hamsters (Group 5, primary + secondary infections) appeared to maintain these higher levels of Paneth cell counts, without any detectable change in cell density/crypt in the period 10, 17, 24 and 31 days p.c. (regression of Paneth cells/mm2 of mucosal tissue on days after challenge, confined to Group 5; Rp = 0·037, n = 20, P = N.S.). The results reported in this paper show clearly that despite tolerating long-lasting chronic infections with the hookworm, A. ceylanicum, hamsters undergo profound changes in the mucosal environment that are typical of Th2-driven immune responses generated by helminths in the mammalian gut. Notwithstanding the intense changes occurring in the mucosa, PAK6 some adult worms appeared to be remarkably resilient and survived for lengthy periods of time in the grossly abnormal

environment of the inflamed intestine in both primary and challenge infections. In this study, hamsters given a primary infection with 50L3 still had adult worms 73 and 94 days later. Despite the length of time from infection to examination, the infected animals had remarkably high mast cell, goblet cell and eosinophil counts, and markedly reduced villi and hypertrophied crypts. These data extend those reported in our earlier paper in which animals were subjected to heavier infections and studied only until day 42 p.i. and support also the idea that the persistence of the inflammatory changes is attributable to the surviving adult worms. Nevertheless, none of the animals in the current study showed overt clinical signs of infection, indicating that hamsters can sustain and tolerate a long drawn out mucosal inflammatory response, lasting for weeks.