Abstract

Thymus plays an important role in the development and regulation of immune responses and other physiological processes. The present study aimed to examine the morphological and immunohistochemical changes of the thymus in Haysex Brown cross chickens with regard to their age. The morphofunctional studies of thymus were performed to determine and analyze age-related changes in anatomical (absolute and relative thymus mass), histological (area of the thymus cortex and medulla, area of connective tissue base, cortex index, number of thymic corpuscles in the lobule), and immunohistochemical (subpopulations of lymphocytes with surface markers CD4+ and CD8+ and their differentiation status) indexes. The study demonstrated that maximum morphological development of thymus could be observed in 20 and 40-day-old chickens. Up to 20 days of age, thymus mass increased proportionally with the chicken body weight. The results indicated that 40-day-old chickens had 1.46 times increase in the cortex index, compared to 20-day-old birds and 1.82 times compared to 8-day-old birds. An increase in the density and number of T-lymphocytes with surface markers (CD4+) and was evident through aging. Regarding aging-associated alternations, the differentiation index (CD4+: CD8+ ratio) reached 1.26±0.09, 1.52±0.25, and 1.56±0.23 in 40, 90, and 110-day-old chickens, respectively. The histological and cell parameters of the thymus in clinically healthy chickens can be used as indicators of normal functioning and to diagnose immunodeficiency in birds.