Thymic Rejuvenation by Adult Grafts in the Lymph Node

Abstract

Immunologic aging is defined as a process in which the immune system undergoes tremendous decline in T cell numbers and function, thus affecting one’s ability to effectively mount an immune response. The degeneration of the thymus, the primary immune organ responsible for T cell development, is central to immunologic aging. Various studies have assessed thymic regeneration as an effective way to offset immune function decline. In this study, we determined the effect of mouse adult thymus transplants in the lymph node of athymic nude mice to rejuvenate thymus function. We transplanted thymuses of increasing ages and assessed engrafted ectopic thymuses by histology as well as for blood T cell numbers and function. We observed that transplanting aged thymuses, up to 8 months old, in the lymph node regenerated thymus function and corresponding T cell activation with some thymic rejuvenation when compared to the expected native thymus in control animals. However, transplanting 11- and 14-month old thymus in the lymph node had decreased-to-limited thymic function with no thymic rejuvenation detected. These observations provide important insights into the plasticity and regenerative capabilities of the thymus during age-associated involution.