title: Nasopharyngeal tonsils (adenoids) contain extrathymic corticothymocytes.
abstract: Adenoidal tissue (also known as nasopharyngeal tonsils) of 58% of humans in the pediatric age group contains immature T-lymphoid cells with the phenotype of thymocytes (TdT+, CD1abc+, cytoplasmic CD3+, coexpressing CD4 and CD8, lacking an Intraepithelial Lymphocyte-associated phenotype). The notable difference in comparison to palatine tonsils is the clustering in groups and sheets, comprising hundreds or thousands of cells (1.7%±0.2 of total T cells). The thymic epithelium is morphologically and phenotypically absent. Adenoids share with tonsils and lymph nodes the presence of immature B cell precursors (TdT+, CD1a-, Pax5+, Surrogate light chain±), however in these latter the presence of TdT+, CD1a+, Pax5- precursors is absent or limited to individual cells. Human adenoids are distinct among the Waldeyer's ring lymphoid tissue because of the known embryogenic derivation from the third pharyngeal pouch, from which the thymus develops; in addition, they may display phenotypic incomplete features of a vestigial thymus.
authors.affiliation: Anatomic Pathology, Department of Surgery and Translational Medicine, Universitá degli Studi di Milano-Bicocca, Milano, Italy.
authors.forename: Serena
authors.initials: S
authors.lastname: Buscone
authors.affiliation: Otolaryngology, Department of Surgery and Translational Medicine, Universitá degli Studi di Milano-Bicocca, Milano, Italy.
authors.forename: Werner
authors.initials: W
authors.lastname: Garavello
authors.affiliation: Anatomic Pathology, Department of Surgery and Translational Medicine, Universitá degli Studi di Milano-Bicocca, Milano, Italy; Pathology, Azienda Ospedaliera San Gerardo, Monza, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Pagni
authors.affiliation: Otolaryngology, Department of Surgery and Translational Medicine, Universitá degli Studi di Milano-Bicocca, Milano, Italy.
authors.forename: Renato Maria
authors.initials: RM
authors.lastname: Gaini
authors.affiliation: Anatomic Pathology, Department of Surgery and Translational Medicine, Universitá degli Studi di Milano-Bicocca, Milano, Italy; Pathology, Azienda Ospedaliera San Gerardo, Monza, Italy.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Cattoretti
mesh_terms: D000234:Adenoids / Q000166:cytology / Q000276:immunology*; D000943:Antigens, Differentiation / Q000276:immunology*; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D008297:Male; D014066:Palatine Tonsil / Q000166:cytology / Q000276:immunology*; D060168:Thymocytes / Q000166:cytology / Q000276:immunology*
chemical_list: D000943:Antigens, Differentiation