Immunochemistry of Fasciola hepatica in the rat model

The excretions, secretions and surface components of a parasite are by their nature centrally involved in the host/parasite interaction. Rats, like cattle, are capable of developing resistance to fasciolosis after primary infection and are therefore considered a suitable laboratory model for cattle. The objective of this study was to characterise the excretory/secretory (ES) and surface components of Fasciola hepatica as it develops in the rat, and to identify those components involved in the host/parasite interaction that may have diagnostic and/or protective value. Three trials were conducted during the study in order to produce supplies of rat antiserum which was protective against F. hepatica, Rats were infected with either 10 (first trial) or 20 (second and third trials) F. hepatica metacercariae as information from the literature indicated that these doses were adequate to stimulate the production of protective antibody levels. The rat sera from the three trials were checked for the presence of protective antibodies by passive protection studies. Only in the latter two trials was the level of protection conferred on recipient statistically significant. The probable causes for the lack of significant protection in trial 1 are discussed. The silver stained protein profiles of ES from newly excysted (D0) flukes and one-day old (D1) flukes were characteristic and were similar to each other. The ES of parenchymal 14-day old (D14) and adult (D56) flukes were markedly different from D0 and D1 flukes but similar to each other. The silver stained total ES protein profiles of the developing flukes were very different from the total biosynthetically (35S-methionine) radio-labelled ES protein profiles. Possible reasons for this are discussed. However, as with the total silver stained ES protein profiles there were clear changes in the profiles of the biosynthetically radio-labelled ES as the flukes developed. It is suggested that these differences in the ES products may reflect the changing environment and activities of the flukes. The possible functions of the changing ES products are discussed.