The intestinal immune response of the mouse to the tapeworm Hymenolepis diminuta

It is now conclusively evident that the intestinal tapeworm Hymenolepis diminuta in the mouse can establish successfully, but is thereafter rejected by an immunological mechanism that is thought to be thymus-dependent. The lack of damage to the small intestine in H. diminuta infection makes this an almost unique and potentially valuable model for the investigation of intestinal immune responses. The work presented in this thesis was undertaken to more fully characterise this host-parasite system, and the nature of the immune response of the mouse to H, diminuta was investigated in four different aspects. Firstly, the thymus-dependency of the response was confirmed, and the role of antibody in the expulsion of H. diminuta investigated; secondly, the source of the antigens which stimulate the protective response was investigated; thirdly, a study was made of the effect of an intestinal response to an unrelated parasite on H. diminuta and H. microstoma in rats and mice; fourthly, lymphocytes from the mesenteric lymph nodes of infected mice were tested for their ability to transfer immunity between mice, and to migrate to the small intestine of infected mice. The effects of pregnancy and lactation in the mouse were studied in relation to rejection of H. diminuta; both phases of the reproductive cycle are known to cause depression of T effector lymphocytes, whereas antibody responses are unaffected or enhanced. It was shown that pregnant and lactating mice reject H, diminuta more slowly than nulliparous mice, and that growth of the worms is much enhanced in comparison with worms from nulliparous mice. The delay in rejection caused by lactation was found to be greater than that observed during pregnancy, from which it can be concluded that immunodepression is more marked in lactating mice. The period of slowest rejection coincides with the period when greatest growth of the worms was noted (i.e. during mid-lactation), but the relative contributions of the immunodepression and the increased food intake of pregnant and lactating mice to the enhanced worm growth are far from clear. It was demonstrated that the immunological defect operating during pregnancy and lactation lies in the effector arm of the response, as sensitisation against H. diminuta occurred normally in these animals, but the response to reinfection of previously immunised animals was shown to be depressed during pregnancy and lactation. Experiments were carried out in which immunisation of mice with H, diminuta failed to provide any protection against H, diminuta infection in their offspring; antibody transferred in colostrum had no effect on either growth or survival of the worms in the young mice, which have little innate capacity to respond to the infection. From these and the above experiments, it was concluded that anti-worm antibody in the absence of effective T lymphocyte function has no measureable independent effect on H. diminuta. The relative roles of the scolex and strobila of H. diminuta in stimulating the immune response of the mouse were investigated by transplantation of worms with large or small weights of strobila into the duodenum of mice. It was found that the larger worms were rejected more quickly by the mice, and it is argued that this difference was not due to the smaller worms being more resistant to immunological attack, or to a time-related exposure of protective antigens, but to differences in size or surface area. Confirmation of this idea came from studies with stunted worms derived from heavily irradiated cysticercoids. At 35 krad and above, the worms excyst normally, but show little growth thereafter. These stunted worms, which cosist of a scolex and a stump of undifferentiated neck tissue, were rejected by mice via an immunological mechanism, but were shown to be poorly immunogenic; they are rejected slowly by mice, and stimulate poor immunological memory in comparison with normal worms. It was concluded that the protective antigen(s) arise from the tegument, but that the anterior end of the worm is more antigenic per unit weight than the posterior end. This theory is shown to fit many established observations, and brief discussion is made of the implications for vaccination studies, and of the possible nature of the protective antigens from the tegument of the worm. (Abstract shortened by ProQuest.)