Phenotypic Analysis of the Chicken Thymic Microenvironment During Ontogenic Development

The development of monoclonal antibodies (mAb) reactive with the thymicmicroenvironment has identified distinct subpopulations within the stromal component,but the function of these subregions in intrathymic T-cell differentiation remainsessentially an enigma. In this study, we have used such a panel of mAb to examine thechicken thymus during ontogenic development to gain insight into the contributions ofthese thymic regions to the distinct phases of T-cell development and to furthercharacterize the development of this organ. Our reagents have demonstrated thecomplex differentiation of the primitive endodermal epithelium into more specializedstructures and the development of other thymic stromal components frommesectodermal cells. We also describe molecules localized to the subcapsular andperivascular regions, which have an ontogenic expression corresponding to the earlylocalization and stimulation of thymic precursors and another molecule on themedullary vasculature expressed corresponding to the exit of mature cells from thethymus. In addition, two markers of distinct medullary epithelial clusters are initiallyexpressed corresponding to the appearance of T-cell receptor-1 (TcR-1) and TcR-2positive cells in the medulla, respectively. These mAb potentially represent excellentreagents for further definition of the thymic modulation of T-cell differentiation.