Localization of foetal antigen 2 (FA-2) in foetal and adult human skin.

Foetal antigen 2 (FA-2) is a connective-tissue-associated antigen isolated from second trimester human amniotic fluid. FA-2 has an alpha-electrophoretic mobility and is a single-chain molecule with a molecular weight of 26 kDa as determined by polyacrylamide gel electrophoresis (PAGE). Using indirect immunofluorescence and the immunoperoxidase technique, FA-2 was found to be in the lamina densa/sublamina densa region of the basement membrane zone (BMZ) in adult as well as in foetal skin. FA-2 was found throughout the dermis in foetal skin, whereas in adult skin it was found to be associated with the BMZ and around the blood vessels, hair follicles and eccrine glands. Intracellular FA-2 antigen was demonstrated in proliferating fibroblasts by the indirect immunoperoxidase technique and immunoelectron microscopy of the fibroblasts revealed staining of the antigen in the cisternae of the rough endoplasmatic reticulum at the trans-side of the Golgi complex as well as in vesicles close to the plasma membranes. FA-2, a hitherto undescribed antigen associated with human BMZ, is probably being synthesized by proliferating fibroblasts.