Hymenolepis diminuta infections in congenitally athymic (nude) mice: worm kinetics and intestinal histopathology.

Congenitally athymic (nu/nu) mice and their thymus-bearing (+/nu) littermates were used to study the effect of a tapeworm, Hymenolepis diminuta, infection, particularly the worm kinetics and histopathology of the small intestine. Groups of nu/nu and +/nu mice were infected once with 5 cysticercoids and examined for 20 days post infection. Worms were expelled both in nu/nu and in +/nu mice, albeit earlier in the latter animals. In both groups specific antibodies could be detected. The antibody titre was highest in the +/nu mice, which also formed more pyroninophilic, including plasma cells. The number of eosinophils increased significantly in the infected nu/nu mice, but not in the +/nu mice. A significant increase in mast cells and globule leucocyte formation was observed in the infected +/nu mice, but none of these cells were found in nu/nu mice which also expelled the worms. No changes in the villus/crypt ration in the jejunum were observed. The mitotic index of the epithelial crypt cells in the jejunum increased in the infected nu/nu mice reaching a peak at day 16 post infection. After re-infection nu/nu mice were not able to expel worms earlier than after primary infection. In passive immunization experiments with serum from both infected nu/nu and +/nu mice no conclusive evidence was obtained for a role of serum antibodies in host protection. It was concluded that host protection to the tapeworm, H. diminuta was dependent on the number of worms and worms could be expelled in the absence of functional T-cells. The hypothesis was put forward that the functional antigens are related to the scolex region and not to the total worm mass.