Immunolocalisation of cell surface peptidases in the developing human breast.

The immunocytochemical distribution of three cell surface peptidases was investigated in samples of developing infant breast ranging in age from newborn to 9.5 months. We have previously demonstrated that in the adult breast these enzymes identify subpopulations of epithelial cells and fibroblasts. We therefore wished to address two questions: (a) At what stage in breast development can fibroblast subpopulations be identified, and (b) Is the distribution of these peptidases related to cellular differentiation and morphogenesis? At the histological level there was a cuff of stromal cells closely associated with the developing ductular and lobular structures. At all stages of ductular and lobular development the fibroblasts in this layer were consistently negative for dipeptidyl peptidase IV (DPP IV) and clearly distinguished from the fibroblasts in the surrounding matrix, some of which expressed DPP IV in an age-dependent manner. Within the infant breast aminopeptidase N (APN) was localised to luminal epithelial cells and all fibroblasts, whilst neutral endopeptidase (NEP) was specifically localised to myoepithelial cells. These results are considered in relation to the role of stromal-epithelial interactions during morphogenesis and the proposed function of these enzymes.