Formation of Morphologically Unusual Features, Associated with Immunodeficiencies, in Lymph Nodes of Gnotobiotic Rats Exposed to a Conventional Milieu

Abstract

Athymic animals are characterized by unusual features in lymph nodes, which are indicative of immunodeficiencies. These features include hypertrophy of follicles, atrophy of the peripheral cortex above the center of deep cortex units, and the formation of lymphocyte clusters at the periphery of these units as well as of compartment replicas in the capsules. Such features were recently observed in some nodes of a minority of aged euthymic animals and we concluded that they probably also reflected immunodeficiencies, since immunodeficiencies may emerge in aging euthymic animals. In an attempt to validate this conclusion, we exposed one-year-old gnotobiotic animals to a conventional milieu, thereby presumably rendering these euthymic animals somewhat immunodeficient, and checked their nodes for unusual features. Nodal unusual features, similar to those encountered in nodes of athymic and of some aged euthymic animals, arose rapidly and the ex-gnotobiotic animals either manifested signs of infections or died. These findings support our previous conclusion that the arising of such features reflects a progressive emergence of a certain state of immunodeficiency with aging.