The binding, internalization, and release of thymocytes by thymic nurse cells

Recent studies in our laboratory have described the development of the SV40-transformed thymic nurse cell (TNC) line SVT-II2, that maintains the ability to internalize thymocytes in vitro. SVT-II2 cells were shown to bind and internalize a subset of the alpha beta TCR+, CD4+CD8+ thymocyte population exclusively. Also, SVT-II2 cells express cell surface class I and class II MHC antigens. These data are consistent with reports that suggest that TNCs may have a role in thymic education. In this report, we used scanning electron microscopy, transmission electron microscopy, and long-term video microscopy to study binding, internalization, and release of thymocytes by TNCs. The results of these experiments showed the internalization event to be selective and dynamic. The process appears to involve programmed cooperation between the two cell types that terminates with the release of selected thymocytes. Although no changes in thymocyte cell surface phenotype were detected as a result of their interaction with TNCs in vitro, over 90% remained viable after a 48-hr incubation period.