ABSTRACT
The thymic defect is the main reason for the laboratory existence of the nude mouse. The defect was discovered in 1968 when the concept of two basically different lymphocyte populations was emerging and led to an explosive proliferation of cellular immunology. One of the major human amnion antigens has been identified in the human embryonic thymus, namely in Hassall’s corpuscles of normal, but not of immunodeficient children. The ectodermal cell layer of the third branchial cleft covers the endodermal portion of the anlage. Since the applied monoclonals label also the epidermal cells in the basal stratum of the skin and of other squamous epithelial linings it may be suggested that the endocrine epithelial thymic cells are of ectodermal origin and that they migrate into the endodermal thymic anlage at different times of organ development.
