PHYLOGENETIC OCCURRENCE OF LYMPHOCYTES WITHIN GUT EPITHELIUM

(I) In thr search for a bursa equivalent in bursaless vertebrates the lymphocytes within the epithelium of the gut have been brought into focus. (2) Some observations on the kinetics of these lymphocytes, the theliolymphocytes, in rats seem consistant with the hypothesis that a bursal function may be exerted by a completely diffuse lymphoepithelial relationship along the gut tract. (3) In this study, the occurrence of theliolymphocytes in the gut of key forms in phylogenetic development is described. (4) The most primitive vertebrates expressing adaptive immunity have few theliolymphocytes. (5) The highest number, close to 50% of the cells of the epithelium, was found in certain fishes which have well developed plasma cell and antibody producing system. (6) The majority of the theliolymphocytes are in most species situated in close proximity to the basement membrane. (7) In amphibians and some reptiles many of the theliolymphocytes are pyroninophilic and some are actually plasma cells. (8) The number of theliolymphocytes per epithelial nuclei as studied here gives an instant picture of the cells in the epithelial compartment. The compartment studied here, we believe, could well turn out to contain an important and hereto neglected component of the lymphoid population. For this reason, it seems pertinent to describe it systematically in the phylogenetic perspective. © 1969 S. Karger AG, Basel.