Interactions between lymphoid cells and a thymic stromal cell line in vitro.

In the present study, we have optimalized the adherence assay to allow monitoring of the level of contact between thymocytes and a thymic epithelial cell line, E-5, in vitro. This type of interaction is not MHC-restricted, thus is unlikely to participate in the education of thymocytes to self. It was also shown that adherence does not vary from strain to strain, except for B6lpr/lpr immunodeficient mice which showed a markedly decreased adherence. This might be caused by the high level of L3T4-, Lyt-2- thymocytes in these mice (Davignon et al., 1985), since enriched double negative cells were shown not to adhere to E-5 cells. Preliminary characterization of adhering thymocytes suggests an heterogeneous mature phenotype. These cells appear around day 16 of fetal life and increase gradually until birth to remain constant throughout life. On the basis of contact duration, two populations of adhering thymocytes exist: one spontaneously detached after 1.5 hr, refractive to further adherence and the other which adheres for up to 14 hr. Contact between lymphoid and E-5 cells was shown to induce PHA responsiveness.