Protection against Fasciola hepatica in the intestine is highly correlatedwith eosinophil and immunoglobulin G1 responses against newly excysted juveniles

Rats were infected with Fasciola hepatica and challenged at regular interva ls up to 38 weeks using an ex vivo gut loop, a technique developed in our l aboratory. The kinetics of the observed immune responses against F. hepatic a in gut tissue and serum were investigated and correlated to protection. I mmunohistochemical methods were wed to measure the frequency of eosinophils , immunoglobulin (Ig)E-positive cells, and mucosal mast cells in the gut lo op, and to determine whether the newly excysted juveniles were coated with IgG antibodies or surrounded by eosinophils, or both. Enzyme-linked immunos orbent assays and a radioimmuno assay were used to measure serum antibody r eactive with newly excysted juveniles. Results showed that protection was h ighly correlated with the frequency of eosinophils and IgE-positive cells i n the gut, but was only moderately correlated with the frequency of mucosal mast cells. Newly excysted juveniles taken from rats exhibiting high level s of protection were always coated with IgG antibodies and surrounded by eo sinophils. Protection was highly correlated with titers of serum IgGI antib odies directed against newly excysted juveniles, but was only weakly correl ated with titers of serum IgA and IgE antibodies. Because protection was hi ghly correlated with IgGI in gut tissue and serum, and with eosinophils in gut tissue, we suggest that IgGI and eosinophils are important in protectin g rats against F. hepatica.