Abstract
Aging is a complex and multifaceted biological process that results in the gradual decline of physiological functions over time. It is associated with reduced performance across multiple systems, affecting metabolic, reproductive, musculoskeletal, and immune functions. While immune aging has been extensively studied in endothermic animals, and in particular mammals such as laboratory rodents, comparatively little is known about how aging manifests in ectothermic vertebrates like reptiles. This study explored the lymphoid tissue (spleen and thymus) of Boa constrictor, a boid snake indigenous to South and Central America and Mexico, but widely kept in captivity all over the world, for potential age-related changes. We observed a significant decrease in cellularity in the spleen, coupled with an increase in organ size correlated with age. In both spleen and thymus the connective tissue of capsule and trabeculae increased significantly with age, indicative of progressive fibrosis. In addition, several changes were observed with increasing frequency in older animals, epithelial hyperplasia in the thymic medulla as well stromal fibrosis and an increasing infiltration by so-called granular cells in both organs. Granular cells likely represent a leukocyte subtype; their presence indicates a progressive chronic low-grade inflammatory state in the lymphoid organs, a feature known as inflammaging in other animal classes. They may also play a role in the progressive fibrosis of the connective tissue. The results firstly describe morphological evidence of aging in B. constrictor and indicate similarities in the aging across animal classes.