Differentiation of epithelial stroma during ontogenesis of the thymus in mice: a speculation on the origin of the thymus as a sensory organ.

Two monoclonal antibodies recognizing subpopulations of epithelial stroma cells of the embryonic mouse thymus are described. Antibody Th-115/7 reacts with epithelial cells of the thymus cortex: antibody Th-101/5 binds to stroma cells of the thymus medulla. In cryosections of whole embryos Th-115/7 bound in addition to mucosal epithelial cells of the pharynx, of the Th-101/5 stained submucosa cells of various regions of the pharynx, of the cavum nasi, of the tongue etc. These observations are compatible with the hypothesis that the thymus anlage originally had developed as a sensory organ at the entrance of the pharynx before it became a primary lymphoid organ.