Dipeptidyl peptidase iv expression identifies a functional sub‐population of breast fibroblasts

The immunocytochemical distribution of the cell‐surface enzyme dipeptidyl peptidase IV (DPP IV) has been studied in the human breast at the light and ultrastructural level. The presence of the enzyme was demonstrated on the cell membranes of interlobular fibroblasts, whilst intralobular fibroblasts were DPP‐IV‐negative. A fluorograph, after immunoprecipitation of 35S‐methionine‐labelled proteins of fibroblasts from primary breast cultures with an anti‐serum to DPP IV, demonstrated a band at 135 kDa consistent with the presence of the enzyme. The clear delineation of 2 functionally distinct sub‐populations of breast fibroblasts was maintained in benign fibro‐adenomas and cystosarcoma phyllodes, both tumour types having growth characteristics of intralobular stroma. This observation has important implications for both normal breast biology and for breast carcinogenesis.