Thymocyte emigration in the chicken: an over-representation of CD4+ cells over CD8+ in the periphery.

We have examined the emigration of chicken thymocytes after intrathymic fluorescein isothiocyanate (FITC) labelling in situ. In this paper we show that in young birds about 0.7% and 0.4% of thymocytes emigrate from the thymus to the blood and the spleen, respectively, per day. This suggests that, as in mammals, most thymocytes die within the thymus. At 3 weeks of age γδ and αβ T cells leave the thymus in comparable levels to their appearance in the blood. The phenotype of recent emigrants in peripheral tissues is similar to that of mature T cells. Interestingly, recent emigrants contain relatively much higher numbers of CD4⁺ and fewer CD8⁺ cells than is observed in peripheral tissues in a steady-state situation. [ABSTRACT FROM AUTHOR]