Alkaline phosphatase positive lymphocytes (APPL) in man

APPL are located in human lymph nodes in almost the same sites as in the laboratory rodents studied up to date. This means that their echotaxis is almost identical and may be an old phylogenetic heritage. But APPL may be found in man until puberty only; thereafter they disappear from all the lymphatic organs. At the age of 40 their depletion is perfected. This evolution of APPL is parallelized by thymus involution. Therefore we may strengthen the conclusion that APPL belong to the T-dependent lymphocytes and that all lymphocytes which really have visited the thymus acquire the enzymatic marker.