Immune responses in Indonesian thin tail and Merino sheep during a primaryinfection with Fasciola gigantica: lack of a specific IgG(2) antibody response is associated with increased resistance to infection in Indonesian sheep

After a primary infection with Fasciola gigantica, the immune responses in a resistant (Indonesian thin tail) and a susceptible (Merino) breed of shee p were analysed. The number of adult flukes recovered from the livers of th e Indonesian thin tail sheep were significantly lower than those found in t he Merino animals. On days 8, 14 and 25 p.i., Indonesian thin tail sheep ex hibited a significantly higher eosinophilia than Merino sheep, whereas neut rophilia was significantly elevated in the Indonesian thin tail sheep on da ys 36 and 48 p.i. Serum from both sheep breeds demonstrated IgM, IgG(1) and IgE responses to F. gigantica. In contrast, the Indonesian thin tail sheep produced significantly lower levels of IgG(2) antibodies relative to the h igh level detected in Merino sheep. The IgE response was biphasic in both s heep breeds with the first response detected by day 14 and the second respo nse developing from days 30 to 60 p.i. Western blotting showed that a simil ar profile of adult fluke antigens was recognised by IgG(1) and IgE antibod ies in both the Indonesian thin tail and Merino sheep. The IgE response was directed to a major antigen at about 92 kDa. We postulate that IgG(2) coul d act as a blocking antibody for protective effector responses against F. g igantica in sheep and that the Indonesian thin tail sheep, by downregulatin g IgG(2) responses, have an enhanced capacity for killing F. gigantica in v ivo. (C) 1999 Australian Society for Parasitology Inc. Published by Elsevie r Science Ltd. All rights reserved.