A fibroblast-associated antigen: Characterization in fibroblasts and immunoreactivity in smooth muscle differentiated stromal cells

Abstract

Fibroblasts with smooth muscle differentiation are frequently derived from human breast tissue. Immunofluorescence cytochemistry of a fibroblast- associated antigen recognized by a monoclonal antibody (MAb), 1B10, was analyzed with a view to discriminating smooth muscle differentiated fibroblasts from vascular smooth muscle cells. The antigen was detected on the cell surface and in cathepsin D-positive and acridine orange-accumulating vesicular compartments of fibroblasts. Ultrastructurally, the antigen was revealed in coated pits and in endosomal and lysosomal structures. 1B10 recognized three major brands migrating at apparent M(r) of 38,000, 45,000, and 80,000, in addition to many minor bands between M(r) 45,000 and 97,000, including M(r) 52,000. The M(r) 45,000 and 38,000 were associated with the cell membrane and M(r) 52,000 as well as M(r) 38,000 were associated with the lysosomes. The 1B10 immunoreactivity was specific to fibroblasts and smooth muscle differentiated fibroblasts within the context of vascular smooth muscle cells.