The adenoid defender of the nasopharynx. A study of the cells in the surface secretion in the nasopharynx

Abstract

The adenoid is implicated in the pathogenesis of upper airway infections (UAI), but in a not yet understood way. In contrast to the adenoid tissue, the surface secretion on the adenoid, which contains not only pathogenic bacteria and viruses but also leukocytes, has attracted little interest. This omission is surprising, especially as leukocytes in the mucosal surface secretions in the sinuses and the tonsils are found to be essential for clearing infections at these sites. The present studies therefore aimed to reveal whether leukocytes migrate from the adenoid into the secretion and, if so, i) are the leukocytes viable, ii) what leukocyte types are represented and iii) are the leukocytes activated? 74 children were enrolled in the studies, 62 with and 12 without a history of frequent UAI. Ten adults served as controls. Samples of adenoid tissue were obtained in connection with adenoidectomy. Samples of surface secretion from the adenoid, and the corresponding mucosal area in the adults, were obtained with an imprint technique. The samples were analysed by light and fluorescence microscopy, immunochemistry, ELISPOT and flow cytometry.The results revealed that B cells, T cells, granulocytes, macrophages and plasma cells migrate into the adenoid surface secretion. The number of leukocytes obtained varied between 210.000 and 3.100.000, of which about 87% were viable. Proliferating lymphocytes were found both in the epithelium and in the secretion, indicating clonal expansion.A large proportion of the immunocytes in the secretion actively produced IgA, IgM and IgG, with a dominance of IgG immunocytes.Phagocytosis observed in the adenoid secretion in children with and without recurrent UAI was significantly correlated to the number of bacteria in the secretion. A large proportion of the T cells in the adenoid surface secretion were activated and some possessed NK-cell like activity.Conclusions: The adenoid supplies the surface secretion with large numbers of viable, morphologically intact leukocytes. This population of leukocytes produces immunoglobulin and has phagocytic capacity. In all probability, the leukocytes play an essential role in the control of the microbial flora and, possibly, the inflammatory processes in the nasopharynx.