The Harderian gland, its secretory duct and porphyrin content in the Plains mouse (Pseudomys australis).

The Harderian gland of the Australian Plains mouse (Pseudomys australis) consists of tubules lined by a single layer of epithelial cells with a surrounding meshwork of myoepithelial cells. The epithelium contains three types of cell. Type I cells, characterised by their many large apical lipid vacuoles, are comparable with cells reported in other rodents. Secretion is exocytotic and, to a lesser extent, apocrine. Type II cells are highly distinctive with extremely large mitochondria arranged in stacks and whorls. Unusually for Harderian glands, these cells possess prominent conventional Golgi complexes and lysosomes. Cytoplasmic 'slashes', possible vacuole-precursors, are also present. Type III cells have few distinguishing features and may be resting cells. They are occasionally binucleate and mitotic figures occur. The gland contains stored porphyrins, chiefly protoporphyrin, in the form of solid intraluminal accretions. There is a marked sex difference, with females having higher levels of porphyrin than males. Among the components of the interstitial tissue are mast cells, plasma cells and porphyrin-containing macrophages. The secretory duct contains large quantities of cell debris, including nuclei, and is lined by columnar cells with single large apical vacuoles. The outer opening of the duct is lined by mucus-secreting cells and stratified squamous epithelium.