Fasciola hepatica: influence of thymus function on the course of infection in mice.

The mouse has been shown to be a suitable experimental host in studies of the resistance to Fasciola hepatica infection. The present experiment compares the course of infection in two different strains of mice, including immunodeficient (congenitally athymic (nude)--(nu/nu)) mice. It was found that the infection was lethal in nu/nu mice, whereas nu/nu mice reconstituted with a neonatal thymus graft reacted as intact mice. The white blood cell picture of nu/nu mice remained unchanged during the infection and between day 24 and 30 after inoculation nearly all nu/nu mice died. Thymus-bearing mice showed blood leucocyte increase and neutrophilia from week 3 after primary inoculation. Furthermore, a marked peritoneal cell reaction occurred 2--4 weeks after primary inoculation. The total number of cells in peritoneal cavity increased approx. 10--15 times and a very remarkable eosinophil peak was seen in week 3 after primary inoculation. In nu/nu mice the peritoneal cell increase was approx. twice that of uninoculated mice and no eosinophil response was observed. When results obtained with the various groups of mice are compared, it appears that resistance to F. hepatica during infection is dependent on a functional thymus.