Human thymus contains amnion epithelial antigens.

Antibodies produced in rabbits to detergent-solubilized human amnion were found to react with Hassall's corpuscles in human thymus. Following nomenclature for placental antigens, the immunogenic group responsible for these antibodies has been tentatively designated as amnion antigens 1 (AA1). The anti-AA1 antisera did not react with other thymic components, nor did they react with any other extra-embryonic tissues than amniotic epithelium. Some adult ectodermally derived tissues, such as breast ductal and corneal epithelium, reacted with anti-AA1, but others such as skin and vagina did not. These findings link an antigenic relationship between amniotic epithelium and certain ectodermal derivatives. Amnion exists long before these tissues are formed, raising the possibility that amniotic epithelium may play an inductive role in their development.