Developmental Expression of IL-2-Receptor Light Chain (CD25) in the Chicken Embryo

Abstract

Thymocyte differentiation obeys the same fundamental principles in mammals as in avianspecies. This parallelism does not only affect the developmentally controlled acquisition ofCD3, 4, 8, and TcR isotype expression, but also concerns CD25, the light chain of the interleukin-2 receptor (IL-2R). On chicken thymocytes, surface CD25, which is recognized by themonoclonal antibody INN Ch16, is first observed during day 11 of embryonic life, and peaksat day 14, when it is expressed by about one-third of all lymphoid cells. CD25 is found onsubsets of all ,thymocyte populations as defined by TcRαβ, TcRγδ, 2, CD4, and CD8 expression,cortical or medullary localization, and is also present on a subset of intrathymic nurse-celllymphocytes. These findings suggest phylogenetic conservation of the IL-2/IL-2R-triggereddifferentiation pathway previously described for mammalian species, thus under-liningits probable functional importance.