[The palatal tonsils as a part of the lymphatic system. Inflow and outflow of newly-formed lymphocytes].

Many lymphocytes continuously migrate from one lymphoid organ to another. The tonsils are also included in the migratory stream of long-lived lymphocytes. We investigated the question whether newly formed lymphocytes, for example, those produced in the spleen or mesenteric lymph nodes, also migrate to the tonsils and to which compartment. The spleen and mesenteric lymph nodes of normal young pigs were selectively labelled with the DNA precursor 3H-thymidine and one day later smears and sections of the tonsils were autoradiographed. About 1% of all spleen-derived young lymphocytes and about 0.5% of all emigrated mesenteric lymph node lymphocytes were found in palatine tonsils. These were almost exclusively small to medium sized lymphocytes. These cells were mainly found in the interfollicular area around high endothelial venules. Surprisingly high numbers were also located in the reticular epithelium of the crypts, in the corona and even in follicles. In a second series of experiment palatine tonsils were selectively labelled by multiple minute injections of 3H-thymidine. The follicles showed a very high labelling index but labelled lymphocytes were also identified in other compartments. One day later tonsil-derived lymphocytes were found in the spleen and lymph nodes. There is thus a continuous exchange of newly formed lymphocytes between the tonsils and other lymphoid organs.