The tonsillar immune system: its response to exogenous antigens

The palatine tonsil is the only lymphoid organ directly exposed to the outside environment. This characteristic anatomical feature appears to be immunologically significant with the defence activity primarily directed against exogenous antigens. However, the palatine tonsil is also often the site of secondary diseases, such as focal infections. This study investigated how the tonsil responds to horseradish peroxidase (HRP) dropped into the crypts and the effects of this response on the regional lymph node and the kidney as a distant organ. HRP entered through the microcrypts was phagocytosed by macrophages, gathered mostly around the vessels and emigrated to the regional lymph nodes. Anti-HRP antibody-producing cells were observed not only in the tonsil but also in the regional lymph node. In this long-term study with repeated immunization, fusion of the epithelial foot process and reduction of the anionic charge in the glomerulus were often found electron microscopically. This investigation suggests that the tonsil has important roles in the defence activity in relation to the general immune system; otherwise it becomes a primary site for focal infections.