A fibroblast is a type of cell that synthesizes and maintains the extracellular matrix of many animal tissues. Fibroblasts provide a structural framework (stroma) for many tissues, and play a critical role in wound healing. They are the most common cells of connective tissue in animals.

Fibroblasts have a branched cytoplasm surrounding an elliptical, speckled nucleus having 1 or 2 nucleoli. Active fibroblasts can be recognized by their abundant rough endoplamic reticulum. Inactive fibroblasts, which are also called fibrocytes, are smaller and spindle shaped. They have a reduced rough endoplasmic reticulum. Though disjointed and scattered when they have to cover a large space, fibroblasts when crowded often locally align parallelly in clusters.

The main function of fibroblasts is to maintain the structural integrity of connective tissue by continuously secreting precursors of the extracellular matrix. Fibroblasts make collagens, glycosaminoglycans, reticular and elastic fibers, and glycoproteins  found in the extracellular matrix. In growing individuals fibroblasts are dividing and synthesizing ground substance. Tissue damage stimulates fibrocytes and induces the mitosis of fibroblasts.

Endogenous peroxidases in normal human dermis

• a marker of fibroblast differentiation. PMID: 6863983

ER-TR7

• reticular network (RN) can be clearly visualized by fluorescence immunohistochemistry coupled with confocal imaging using a monoclonal antibody, ER-TR7. PMID: 15237106
• reticular fibroblasts express ER-TR7. PMID: 12900524
• a putative marker of connective tissue in lymphoid organs. PMID: 11880143
• the interstitial cells were identified as interstitial fibroblasts by immunostaining with ER-TR7. PMID: 10792616
• majority of cells in all colonies were positive for the connective tissue marker ER-TR7. PMID: 3424418
• detects reticular fibroblasts, which constitute the cellular framework of lymphoid and nonlymphoid organs and their products, and it reacts with an intracellular component of fibroblasts. PMID: 3519751

Fibroblast-specific protein 1 (FSP1)

• a specific marker for fibroblasts. PMID: 16105038, PMID: 7615639

MAS516

• reacts with surface membrane molecules expressed by human fibroblasts, tissue macrophages and peripheral blood monocytes. PMID: 7829129

prolyl 4-hydroxylase (5B5)

• cytoplasmic marker of human fibroblasts, and specifically involved in the synthesis of collagen  PMID: 1611660, PMID: 1760520
• considered as a typical fibroblast marker, reacts with human prolyl-4-hydroxylase which is an intracellular enzyme related to collagen biosynthesis. PMID: 7829129
• a putative marker of collagen-producing cells and, therefore, in this context, of fibroblasts, and it reacts with the beta subunit of proline-4-hydroxylase, the enzyme which catalyses the formation of 4-hydroxyl proline in collagen and other proteins with collagen-like amino acid sequences. 5B5 is expressed by a proportion of synovial intimal cells and by fibroblasts in the underlying connective tissue in normal, OA and RA synovia. PMID: 9566669
• Tissue from patients who had Dupuytren disease was examined immunohistochemically with the 5B5 antibody, which is a marker for fibroblasts. PMID: 7822340
• also expressed in epithelial, endothelial as well as interstitial cells and in alveolar macrophages. PMID: 7856409, PMID: 2737246
• 5B5-alpha identifies active but not resting fibroblasts. PMID: 2165882
• 5B5 to prolyl 4-hydroxylase stained human umbilical vein endothelial cells (HUVEC) as well as synoviocytes and FB. PMID: 8082888
• 5B5 were used to localize the beta subunit in human extraembryonic tissues. The strongest sites of 5B5 reactivity were extravillous cytotrophoblasts in the basal plate, uteroplacental arteries and amniochorion, syncytiotrophoblast displayed variable weaker reactivity. PMID: 8244775