Phenotypic Mapping of The Chicken Embryonic Thymic Microenvironment Developing Within an Organ Culture System

The chicken thymic microenvironment, as it developed in an embryonic thymus organculture system, was phenotypically mapped using a panel of mAb defining bothepithelial and nonepithelial stromal cell antigens. We have previously reported thatthymocyte proliferation and differentiation will proceed for up to 6–8 days in thymusorgan culture, hence demonstrating the functional integrity of the thymicmicroenvironment in vitro. During this time, the stromal component reflected that of thenormal embryo with cortical and medullary epithelial areas readily identifiable by bothmorphology and surface-antigen expression. An abundance of subcapsular and corticalepithelial antigens was detected in the cultured thymus, particularly those normallyexpressed by the epithelium lining the capsule, trabeculae, and vascular regions (typeepithelium) in the adult and embryonic thymus. Medullary epithelial antigensdeveloped in organ culture, although were present in lower frequency than observed inthe age-matched embryonic thymus. MHC class II expression by both epithelial andnonepithelial cells was maintained at high levels throughout the culture period. Withincreasing time in culture, the ratio of epithelial to nonepithelial cells decreased,concurrent with a decrease in thymocyte frequency and suggestive of a bidirectionalinteraction between these two cell types. Thus, a functionally intact thymicmicroenvironment appears to be maintained in embryonic thymus organ culture, amodel that is currently being exploited to assess the role of stromal antigens, as definedby our mAb, in the process of thymopoiesis.