The human adenoid. A morphologic study.

Abstract

OBJECTIVE: We examined the route by which antigen on the surface of the adenoid may be brought into contact with the lymphoid follicles in the submucosa of the adenoid. DESIGN: We studied under light and electron microscopy 13 adenoids from children undergoing elective surgery. Portions of all of the specimens were fixed in formalin and embedded in paraffin and plastic for hematoxylin-eosin and periodic acid-Schiff staining. Portions of four adenoids were fixed in glutaraldehyde for electron microscopy. RESULTS: Two major types of epithelium were evident by light microscopy: a ciliated or squamous epithelium containing few lymphocytes and a nonciliated-flat epithelium with a heavy infiltration of lymphocytes ("lymphoepithelium"). Scanning microscopy showed the surface of this lymphoepithelium to be composed largely of cells with multiple microfolds known as M-cells. Freeze-fracture technique showed many lymphocytes under the M-cells. Transmission electron microscopy showed the lymphocytes to be located in compartments formed by the epithelial cells. Light microscopy study of 50 serial sections embedded in plastic suggested that the compartments communicated to form intraepithelial channels for the lymphocytes. CONCLUSION: The epithelium of the adenoid has areas with ciliated epithelium adjacent to areas with epithelium containing M-cells and intraepithelial lymphatic channels. HYPOTHESIS: The lymphoepithelium of the adenoid is a mechanism for transporting antigen via the M-cells to the underlying lymphoid follicles.