Subset-Specific Regulation of the Lymphatic Exit of Recirculating Lymphocytes In Vivo

The blood-to-lymph recirculation of lymphocytes is required for the maintenance of immune surveillance and the dissemination of memory. Although the ability of lymph-borne cells to recirculate has been well documented, relatively less is known about the migration capacity of PBLs. We have found a clear preference for PBLs to recirculate through s.c. rather than intestinal lymph nodes. This preference could be directly attributed to the migratory characteristics of γδ-T cells. γδ-T cells were found to express significantly higher levels of L-selectin than other subsets, suggesting that at least some of this preferential migration could be attributed to their interaction with ligands on vascular endothelium. More detailed experiments showed that γδ-T cells migrated through lymph nodes with greater efficiency than αβ T cells or B cells, which clearly indicated an enhanced ability of γδ-T cells to exit lymph nodes in the efferent lymph independent of entry from the blood. This hypothesis was supported by histological examination, where γδ-T cells were found almost exclusively in the interfollicular traffic areas within lymph nodes. These data indicate that γδ-T cells are the most active recirculating lymphocyte subset in ruminants and suggest new mechanisms to regulate the traffic of lymphocyte subsets through normal lymph nodes.