ROLE OF CATHEPSIN-D IN THE DEGRADATION OF HUMAN SERUM-ALBUMIN BY PERITONEAL-MACROPHAGES AND VEILED CELLS IN ANTIGEN PRESENTATION

Murine peritoneal macrophages (PMO) and veiled cells (VC) isolated fro m the thoracic duct of irradiated lymphadenectomized (MNLX) mice prese nted intact human serum albumin (HSA) to stimulated T lymphocytes, but VC were not as effective as PMO in presenting the antigen. Pepstatin A significantly inhibited the presentation of HSA by VC. Lysates prepa red from PMO degraded [I-125]HSA at pH 4.0 to peptides as demonstrated by SDS-polyacrylamide-gel electrophoresis and autoradiography. Degrad ation was inhibited by pepstatin A, suggesting that cathepsin D might be responsible for processing the antigen. In contrast, lysates prepar ed from VC did not degrade [I-125]HSA. The localization of cathepsin D , by light microscopy, was examined on cytospins of PMO and VC by mean s of a peroxidase anti-peroxidase technique (PAP). Cathepsin D was fou nd in vacuoles in the cytoplasm of PMO and, in some cases, appeared to be bound to some areas of the cell surface, but the enzyme could not be detected in VC.