Subset-specific regulation of the lymphatic exit of recirculating lymphocytes in vivo

The blood-to-lymph recirculation of lymphocytes is required for the mainten ance of immune surveillance and the dissemination of memory. Although the a bility of lymph-borne cells to recirculate has been well documented, relati vely less is known about the migration capacity of PBLs, We have found a cl ear preference for PBLs to recirculate through s,c, rather than intestinal lymph nodes. This preference could be directly attributed to the migratory characteristics of gamma delta -T cells. gamma delta -T cells were found to express significantly higher levels of L-selectin than other subsets, sugg esting that at least some of this preferential migration could be attribute d to their interaction with ligands on vascular endothelium, More detailed experiments showed that gamma delta -T cells migrated through lymph nodes w ith greater efficiency than cup T cells or B cells, which clearly indicated an enhanced ability of gamma delta -T cells to exit lymph nodes in the eff erent lymph independent of entry from the blood. This hypothesis was suppor ted by histological examination, where gamma delta -T cells were found almo st exclusively in the interfollicular traffic areas within lymph nodes. The se data indicate that gamma delta -T cells are the most active recirculatin g lymphocyte subset in ruminants and suggest new mechanisms to regulate the traffic of lymphocyte subsets through normal lymph nodes.