Figure 4.

L-selectin mediates optimal T cell homeostatic proliferation during lymphopenia. Wild type or L-selectin^−/− splenocytes were labeled with CFSE (0.25 μM) and injected (5 × 10⁶ cells) intravenously into RAG-1^−/− recipient mice. Four days after transfer, the recipient spleen was harvested, immunostained to detect T cells, and analyzed by flow cytometry. CFSE fluorescence is decreased by one half with each cell division thus allowing proliferation to be assessed in vivo. The transfer of wild type cells yielded robust homeostatic proliferation of T cells, while the transfer of L-selectin^−/− cells (i.e., excluded from entering the PLN) exhibited much reduced proliferation.