An ultrastructural study of the histopathology of early Taenia taeniaeformis infection in nfr hypothymic mice, reconstituted hypothymic mice and phenotypically normal littermates (parasitology, metacestode)
Description
NFR/nu mice fail to mount an eosinophilic response to Taenia taeniaeformis infection during the first three weeks of infection. Giant cells are absent from lesions and collagen deposition does not occur. The latter observation may be due to the absence of fibroblasts to enter the lesion site. Metacestode cysts in NFR/nu mice are larger and more numerous than they are in NFR/+ mice. Neutrophils are the primary phagocytes in NFR/nu mice with Taenia taeniaeformis infection. Macrophages are not abundant at lesion sites and, where present, rarely exhibit secondary lysosomes. Both neutrophils and macrophages are active phagocytes in lesions in NFR/+ mice. Eosinophils constitute an important feature of the response of NFR/+ mice, and the initial accumulation of these cells is not dependent upon the presence of protective antibody. Neonatal thymus grafts restore NFR/nu mice, and recipients respond to infection with a marked eosinophilic infiltration, giant cell formation, fibroblast accumulation and collagen deposition. Average cyst size and total lesions are comparable to those seen in NFR/+ mice. Thymus-grafted mice do not exhibit the same ability to destroy invading metacestodes as NFR/+ mice. This indicates that inflammatory cells alone are not capable of eliminating the metacestodes, and suggests that some additional host defense mechanism is necessary. Thymocyte injections have no effect upon the inflammatory response, but if thymocytes are given in several injections over a period of time, the numbers of metacestodes which successfully reorganize are adversely affected. Thymocyte suspensions most likely contain predominantly immunoincompetent cells incapable of effecting restoration of the host inflammatory response A fibrotic capsule does not develop about metacestodes in NFR/nu mice. However, a host 'capsule' is apparent at 14 and 21 days post-exposure. This capsule is comprised of an inner area of epitheliod cells and an outer region of transitional macrophages. Development of metacestodes in NFR/nu mice progresses normally. However, during the first ten days of growth bladder volume is two to three times normal recorded values. This size discrepancy is no longer apparent by 14 days post-exposure