Regional variation in macrophage antigen expression by murine epididymal basal cells and their regulation by testicular factors

Factors controlling the appearance in the epididymis of basal cells and their expression of macrophage antigens were examined by ligating the efferent ducts to prevent the entry of spermatozoa in adult and juvenile mice. Fixation and antigen retrieval techniques were developed to preserve tissue morphology and expression of two macrophage antigens in paraffin-embedded epididymal tissue. A combination of periodate-lysine-phosphate fixation, low-temperature embedding and enzyme predigestion of sections permitted immunohistochemical detection of the mature macrophage antigen Mac-1, whereas the panmacrophage marker F4/80 required fixation in neutral-buffered formalin. Epididymal basal cells were immunostained for F4/80 and quantified with avidin-biotin-peroxidase. In the adult mouse, the total number of basal cells per millimeter length of tubule cross section perimeter and the percentage expressing the F4/80-antigen were significantly higher in the initial segment and caput region than in all other epididymal regions. In the initial segment, immunostained basal cells surrounded the tubule in a network, and some extended towards the lumen. Ligation of the efferent ducts to prevent inflow of testicular secretions significantly reduced the number of basal cells per cross section in the initial segment of the adult and juvenile; the percentage of basal cells expressing macrophage antigens in the initial segment and the caput epididymidis was also reduced. Since basal cells still appeared in the ligated postpubertal epididymis, it is concluded that testicular exocrine secretions entering the epididymal lumen around puberty are not the major influence on basal cell appearance in the murine epididymis, but they may modulate their expression of macrophage antigens.