Fibroblasts are cells that form the connective tissue. They can differenciate into distinct connective tissue cells and maintain the extracellular matrix of the fibrous connective tissue. They produce the matrix molecules of scar tissue, among them collagens, hyaluronic acid, glycosaminoglycans and glycoproteins of the extracellular matrix, reticular and elastic fibres or mucopolysaccharides. The latter influence the cell differentiation described above. Fibroblasts also generate important growth mediators for endothelia and cells in form of their Fibroblast Growth Factors (FGFs). Fibroblast activity is regulated, among others, by IL-1 and TNF.

Vimentin is the most frequently found intermediate filament in fibroblasts. Thus, it is a reliable fibroblast marker. The Fibroblast Surface Antigen (SFA) is a glycoprotein produced by connective tissue cells (mesenchymal cells, fibroblasts, and astroglia cells) that is also suited for detection of fibroblasts and fibroblast cell lines.

To mark undifferenciated fibroblasts, antigen CD34 (human hematopoietic progenitor cells) is a good choice. It is distributed in most connective tissues, among them alveolar connective tissue and the connective tissue of skin and blood vessels. A marker for fibroblast differentiation in the human dermis are endogenous peroxidases (B. Coulomb et al., 1983). Immunohistochemistry with Heat Shock Protein 47 (HSP47) showed that it can also be used to mark skin fibroblasts (K. Kuroda und S. Tajima, 2004).

For activated fibroblasts, we recommend procollagen type 1 or Prolyl-4-Hydroxylase beta antibodies, the latter occurring in epithelia, endothelia, alveolar macrophages and in interstitial cells.

To detect myofibroblasts, the anti-alpha-actin antibody with the clone designation 1A4 from smooth muscle tissue can be used. Reticular fibroblasts form the cellular framework of lymphoid and non-lymphoid organs. They express ER-TR7, intracellular components which are thus very practical to use for marking such fibroblast types. The antibody ABIN133811 reacts to an antigen in fibroblast cytoplasm that has not yet been described. It detects reticular fibroblasts of the mouse.

Fibroblast-specific protein 1 (FSP1) can be detected in mice as early as day 8,5 p.c. It occurs in the cytoplasm of fibroblasts, but not in epithelial cells. Rarely, FSP1 antibodies will react to the parenchym. In case of inflammation, epithelial cells are marked by FSP1 antibodies, too, which are thus assumed to be converting to fibroblasts at the site of inflammation (F. Strutz et al., 1995).