ABSTRACT

Genital and immunological organs undergo marked declines due to aging. The immunological decline can incur infections, auto-immune diseases and malignancy. The spontaneously hypertensive rat (SHR rats) are derived from Wistar rats with high blood pressure after serial brother-sister mating. As the name stands for, SHR rats have been used worldwide for studies of human essential hypertension. From the fact that carcinogenesis, either natural or chemically induced, does not differ between in normal mice and nude mice which congenitally do not have thymus, another type of immuno-responsible cells have been identified; that is natural killer (NK) cells. NK cells are found in nearly all mammals. Compared with that in W rats, the activation of NK cells in SHR rats is promoted with aging. Immunologically the most characteristic feature of SHR rats is the non-specifically activated macrophages and NK cells. In particular, abnormally activated macrophages disturb T cell functions directly or indirectly through various suppressive factors and oxygen radicals.