MICROANATOMICAL DISTRIBUTION OF DENDRITIC CELLS IN NORMAL TONSILS

Lymphoid dendritic cells play an essential role in antigen presentatio n in primary immune responses and are believed to be important in norm al healthy responses of the mucosal immune system. The microanatomical distribution of HLA-DR-positive/S100 antigen-positive dendritic cells was analyzed in 10 normal palatine tonsils. Tonsil biopsies were obta ined from 8 normal children undergoing otolaryngological surgery for r easons completely unrelated to tonsil disease. Two samples of normal a dult tonsil were also obtained. Standard immunohistochemical methods, with antigen retrieval, were used to detect cell surface markers in fo rmalin-fixed and/or frozen tissue specimens, The clinical identificati on of these tonsils as normal was confirmed by their microscopic appea rance. HLA-DR antigen expression was restricted to lymphocytes, macrop hages and dendritic cells; all normal epithelia were negative. S100-po sitive dendritic cells were readily detected in surface and crypt epit helium and were rare in submucosal sites or follicles. T cells were ob served as frequently as dendritic cells in epithelial sites. Dendritic cell density was highest in extrafollicular T cell areas, where CD4-p ositive lymphocytes were especially abundant. A significant correlatio n was observed between the total number of different bacterial species isolated from individual normal tonsils and the frequency of dendriti c cells in both the crypt epithelium and extrafollicular T cell areas. The number of dendritic cells at the tonsil surface was not similarly related to the bacterial flora.