Binding of cortical thymocytes to a medullary epithelial cell line: a brief review

In this review, we bring together data regarding complexes formed between thymocytes and a line of thymic epithelial cells, E-5. We show that E-5 has all the markers which identify it as of epithelial and medullary origin. We show that thymocytes which form complexes with it belong to the double positive, CD4 + CD8 + population, and that the receptor responsible for binding to epithelial cells is likely to be an as yet unidentified glycoprotein. The ligand on E-5 cells is also a glycosylated protein. Adhering thymocytes are in a state of mitotic activity, and their incubation with E-5 cells does not induce increased responsiveness to polyclonal mitogens. Non-adhered thymocytes, on the other hand coincubated With E-5 cells increase their responsiveness to ConA and initiate responsiveness to PHA. Differentiation of adhering thymocytes is evidenced by their acquisition of refractoriness to a secondary adherence, and by the modification of their surface phenotype.