Distribution and Age‐Related Changes of IL‐21 Immunopositive Cells in the Thymus of Ostrich Chicks

Artificially reared ostriches face susceptibility to stress, infections, with mortality rates reaching 40% during the brooding phase. The thymus serves as a vital central and lymphoid immune organ, pivotal in combating external antigenic challenges and aiding in T lymphocyte differentiation. This study aims to investigate the distribution and changes of IL-21 in the thymus of African ostrich chicks, offering a morphological foundation for immune modulation and disease prevention in African ostriches. The current study utilized healthy African ostrich chicks aged 1, 15, 30, 45, 60, 75, and 90 days as experimental cohorts. Paraffin sectioning and immunohistochemical techniques were employed to investigate the morphological characteristics, distribution, and development change patterns of interleukin-21 (IL-21) immunopositive cells in the thymus of ostrich chicks. The results revealed that IL-21 immunopositive (IL-21-ip) cells exhibited a round or oval shape and were predominantly situated in the thymic medulla, with some presence in the cortex and at the corticomedullary junction. The expression intensity of IL-21 in the thymus and the density of positive cells exhibited a gradual increase followed by a decrease as the chicks aged. Both the expression intensity and the quantity of positive cells peaked at 75 days old. These results suggest a potential significant role for IL-21 in regulating thymic development in African ostriches.