Microcrypt extensions of tonsillar crypts.

The crypts of human palatine tonsils were examined electron microscopically. The cryptal epithelia contained three types of micropores (termed microcrypt). Type I microcrypts opened between intercellular spaced of the epithelial cells. Free cells were observed in the micropores. Type II microcrypts opened near the center of a cryptal epithelial cell. Type III microcrypts appeared after "specialized epithelial cells" degenerated and fell off. Many mature plasma cells are attached to the walls of the sinusoidal vessels in the lower boundary zone of the epithelium and subepithelial layer. Lymphocytes were observed migrating from the postcapillary venules of the subepithelial zone. The findings indicate that the microcrypts are probably orifices for tunnel-like passages of free cells and that they are located in the walls of the tonsillar crypts. The lymphocytes in the passages perhaps come from lymphoid tissues in the subepithelial layer and postcapillary venules, and the antibodies produced in the cryptal epithelia of the palatine tonsils may contribute to humoral immunity.