Which steps in lymphocyte recirculation are regulated by interferon-gamma?

Lymphocyte traffic throughout the body is a basic mechanism of immune surveillance. Most studies of the regulation of the extravasation of lymphocytes have focused on the interaction between endothelial cells of the high endothelial venules (HEV) in lymphoid organs and lymphocytes via the interaction of various adhesion molecules. Cytokines play a major role in the regulation of immune reactions, and some have been shown to upregulate adhesion molecules important for lymphocyte migration. Using interferon-gamma (IFN gamma) as an example of such a cytokine, we summarize the available data on regulation by IFN gamma of the different phases of lymphocyte migration from the blood via HEV, through the lymphoid organ and finally exiting the organ. Much data obtained in in vitro assays have not yet been confirmed in vivo, and therefore a number of questions remain unanswered. Our hypothesis is that the interaction of lymphocytes with endothelial cells represents just one aspect of regulation, and that lymphocyte migration is probably regulated much more effectively within the lymphoid organ.