Basal cells of the human epididymis--antigenic and ultrastructural similarities to tissue-fixed macrophages.

Very little is known about the basal cells in the epididymal epithelium. Their function is unclear, although they are present in all mammalian epididymides studied. The corpus epididymides from five patients undergoing castration because of prostatic carcinoma were fixed and processed for electron microscopy. Basal cells were characterized by a slightly heterochromatic nucleus with prominent nucleolus, pale round mitochondria, dispersed endoplasmic reticulum, and sparse Golgi apparatus; they were often rich in lipofuscin inclusions, possibly originating from principal cells. Some peritubular macrophages in close proximity to the epithelium were structurally similar to basal cells. Immunohistochemical staining revealed in the epididymides of another ten patients that the basal cells were recognized by the monoclonal antibody (mAb) 25F9 against mature, tissue-fixed macrophages but not by mAbs 27E10 or RM3/1, which were against activated macrophages usually found in acute or late inflammation, respectively. On the basis of the present findings, as a working hypothesis a scavenging role of the basal cells in a local immune defense mechanism is proposed, in which antigenic products (possibly of sperm degradation), taken up by the principal cells, would be phagocytosed by the basal cells. It could be inferred that when the basal cells are overloaded, they would leave the epithelium to be replenished by tissue-fixed macrophages.