Histology of transplantable murine epithelial tumors infiltrated with immature T lymphocytes: Neoplastic analogues of the thymus

Serially transplantable murine thymic and salivary gland epithelial tumors were studied by immunohistologic methods and by electron microscopy. At the ultrastructural level, tumors appear to be identical. The large polygonal epithelial cells lack rough endoplasmic reticulum, Golgi apparatus, and secretory vesicles, and are anchored together by tonofilaments and desmosome junctions. Some areas in the tumors are composed solely of the neoplastic epithelium, while other areas are richly 'infiltrated' with lymphocytes having a cortical thymocyte phenotype and supported by a lacy dendritic network of neoplastic epithelial cells. Immunohistochemical staining demonstrates that the epithelial cells express class I and class II major histocompatibility gene complex (MHC) antigens, epidermal keratin, and the ER-TR4 and ER-TR5 thymic epithelial markers. Lymphocyte-rich regions show homogeneous staining for both L3T4 (CD4) and Lyt-2 (CD8) T-cell antigens.