Macrophages and interdigitating cells; their relationship to migrating lymphocytes in the white pulp of rat spleen.

The pathway of lymphocyte migration through the white pulp of rat spleen and the relationship of migrating cells to the accessory cells (marginal zone macrophages and interdigitating cells, IDCs) of the white pulp compartments were analysed. Donor lymphocytes were obtained from lymph nodes, enriched for T lymphocytes and labeled in vitro with 5-(3H)uridine. They were injected intravenously into syngeneic recipients from which samples of spleen were taken at short intervals from 3 to 300 min after injection. Autoradiographs of semithin and ultrathin sections showed that, in the internal layer of the marginal zone (MZ), lymphocytes tended to accumulate within some regions in close proximity to marginal-zone macrophages before migrating into the periarteriolar lymphoid sheath (PALS). The lymphocytes enter PALS between protrusions of the accessory cells located in the peripheral area of the sheath. During migration towards the central area of PALS, a close contact between both cell types was noted. In the central area of PALS, preferential accumulation of lymphocytes around IDCs was observed. Labeled lymphocyte distribution within PALS and the rate of cell migration through the white pulp seem to depend on lymphocyte-IDC contact. A common feature of accessory cells which may affect the migration of lymphocytes in both MZ and PALS is the presence of Birbeck granules.