Intravenous Labeling and Analysis of the Content of Thymic Perivascular Spaces.

Following development in the thymus, T cells are thought to exit into the periphery predominantly through perivascular spaces (PVS). This exit route is used by conventional T cells, and likely also applies to unconventional T cell subsets, such as precursors of CD8αα and TCRγδ intraepithelial lymphocytes, regulatory T cells and natural killer T cells. Additional cell types might also be found in the PVS and initiate interactions with exiting T cells. The exact content of the PVS, and the processes within, are not well studied. To distinguish vascular from resident cells within various tissues by flow cytometry, intravenous (i.v.) labeling is becoming a commonly employed method. We recently used anti-CD45.2 antibodies and magnetic enrichment to further evaluate this technique, and compared labeled and unlabeled cells in the thymus and blood. This assay can be used to specifically investigate hematopoietic cell subsets within the PVS of the thymus.