An enhanced role for the recirculating lymphocyte in the neonatal immune system

Lymphocytes continually recirculate between the blood and the tissues via t he lymph independent of antigen. A great deal is known regarding both the p hysiology and the molecular mechanisms responsible for the process in adult s. However, relatively little is known regarding the development of the rec irculating lymphocyte pool in very young animals or fetuses. We have direct ly measured the recirculation of lymphocyte subsets in antigen-inexperience d newborn animals, and found extensive recirculation of T cells through bot h intestinal and subcutaneous lymph nodes. Apparent selective migration of recirculating lymphocytes could be attributed to subset-specific migration of gamma delta-T cells through subcutaneous lymph nodes. This clearly demon strates that the preference for gamma delta-T cells to recirculate through SCLN is lineage specific, and independent of the presence of antigen. Most surprising was the observation that the recirculating lymphocyte pool was p roportionately larger in neonatal animals than in adults, which correlated with the histological appearance of newborn lymph nodes. This data strongly suggests that development of the recirculating lymphocyte pool is inversel y correlated with antigen exposure, and decreases in size with age and the acquisition of immunological memory. (C) 2000 Elsevier Science Ltd. All rig hts reserved.