Scanning, transmission and immunoelectron microscopical studies of the tonsil-like lymphoid organ of normal and horseradish-peroxidase-injected laboratory suncuses.

Fine structures of normal and horseradish peroxidase (HRP)-stimulated tonsil-like lymphoid organs of the laboratory suncus (Suncus murinus) were examined by scanning, transmission and immunoelectron microscopies. The normal organs appear as a pair of small oval protrusions at the upper lateral sites of the fauces, and consist of a single lymph nodule with a germinal center and a crypt-like epithelium with prominent lymphoid cell infiltration. Postcapillary venules (PCV) and efferent lymphatics are associated within the marginal region of the nodule and separated from the neighboring pharyngeal tissues. Numerous lympho-plasma cells, interdigitating cells and reticulum cells occurred within the lymphoid parenchyma, as well as in the intraepithelial infiltrating cell populations. In the HRP-stimulated animals, the anti-HRP antibodies producing lympho-plasma cells were often seen in the parenchyma and epithelia; however, similar HRP-antibody-positive lymphocytes were rarely detected in the PCV lumina. In addition, some HRP antibody bearing interdigitating cells were also identified in the same parenchyma. These data indicate that the suncus' tonsil-like organs have a positive immune function to oral antigens, together with the suncus' systemic immune system and it is hypothetically presumed that the organ may correspond to a homologous organ of the human palatine tonsil in comparative anatomy.