Thymic lymphoma cells as a model for complex-formation between thymocytes and thymic medullary epithelial cells

The formation of complexes between thymocytes and thymic stromal elements is known to be involved in T cell differentiation. We have previously described one type of lympho-stromal interaction involving CD4+ CD8+ thymocytes and a medullary epithelial cell line (E-5). In this study we report the potential for complex formation of two different thymic lymphoma cell lines (Ti-6 and RDM-4). Ti-6 cells were shown to adhere to the E-5 cells, while RDM-4 cells were totally incompetent. Phenotypic characterization of these cell lines suggests that immature thymocytes are not capable of forming complexes with medullary epithelium and that a certain level of differentiation is required to do so. Comparison of their phenotypes showed that the possibility of some classical T cell surface markers being the receptor for the E-5 ligand can be dismissed.