The localization of IgA, IgG, IgM, SP and the relationships of plasma cells and lymphocytes to blood vessels in the tonsillar crypt epithelium were investigated. Immunofluorescent techniques were used that included antisera specific for the two antigenic determinants of external secretory IgA, namely, 4s SP and 7s IgA, and also antisera specific for 7s IgG and 19s IgM. The secretory piece was absent in the crypt epithelium and in most of the crypt lumen. Aggregations of plasmacyte series cells, containing either IgG, IgA, or IgM were present in the crypt epithelium. Mature plasma cells of these aggregations abutted against the walls of blood sinusoids located in the epithelium, which suggested secretion into these sinusoids. All three immunoglobulins were also identified between epithelial cells and small lymphocytes. Postcapillary venules with emigrating small lymphocytes abounded in sub-epithelial sites, and were present at the lower border zone of the epithelium. Lymphocytes in shapes of diapedesis were observed in the endothelium of epithelial blood sinusoids. These observations are in accord with the hypothesis that a “circulation” of many lymphocytes occurs in the epithelium facilitating the activation of any one genetically committed lymphocyte.
Crypt Epithelium
