Lymphoepithelial interactions in the mouse thymus: phenotypic and kinetic studies on thymic nurse cells.

Thymic nurse cells (TNC), complexes between epithelial cells and thymocytes, are further characterized. Our results show that TNC are predominantly located in the subcapsular and outer cortical region of the mouse thymus. The enveloped thymocytes display the characteristics of cortical thymocytes. They are PNA+, Thy-1+, Lyt-123+, TL+, ThB+, H-2K+, IA+, and cortisone and radiation sensitive. In vitro cultivation of TNC in the presence of interleukin 2 induces a phenotype change to Lyt-1-, ThB-, Lyt-23+. The yield of TNC is highly dependent on the isolation conditions. Moreover, the thymocytes enveloped by an individual TNC do not constitute a single clone. The latter findings strongly suggest that complete envelopment is probably an isolation artifact. However, the cellular composition of the complexes is not random but rather the result of a preexisting in vivo association between an immature thymocyte subpopulation and outer cortical epithelial cells. TNC represent the in vitro correlate of this in vivo interaction. The implications of these results for intrathymic T cell differentiation are discussed.