Fibrocyte

Fibrocyte is a very old term used to identify inactive mesenchymal cells, that is cells showing minimal cytoplasm,limited amounts of rough endoplasmic reticulum and lack of biochemical evidence of synthesis of proteins. The term "fibrocyte" contrasts with the term "fibroblast." Fibroblasts are connective tissue cells characterized by synthesis of proteins of the fibrous matrix, particularly the collagens. When tissue is injured, the predominant mesenchymal cells, the fibroblast, have been believed to be derived from the fibrocyte or possibly from smooth muscle cells lining vessels and glands. Commonly, fibroblasts express smooth muscle actin, a form of actin first found in smooth muscle cells and not found in resting fibrocytes. Fibroblasts expressing this form of actin are usually called "myo-fibroblasts." Recently, the term "fibrocyte" has also been applied to a blood born cell able to leave the blood, enter tissue and become a fibroblast. As part of the more general topic of stem cell biology, a number of studies have suggested that the blood contains marrow derived cells that can differentiate into fibroblasts. These cells have been reported to express the hematopoietic cell surface markers CD34+, CD45+, as well as as collagen. Chesney J, Bacher M, Bender A, Bucala R. The peripheral blood fibrocyte is a potent antigen-presenting cell capable of priming naive T cells in situ. Proc Natl Acad Sci U S A. 1997 Jun 10;94(12):6307-12.] These cell can migrate to wound sites, suggesting a role in wound healing.Abe R, Donnelly SC, Peng T, Bucala R, Metz CN. Peripheral blood fibrocytes: differentiation pathway and migration to wound sites. J Immunol. 2001 Jun 15;166(12):7556-62.] There are several studies suggesting that fibrocytes mediate wound healing and fibrotic tissue repair.Yang L, et al., Peripheral blood fibrocytes from burn patients: identification and quantification of fibrocytes in adherent cells cultured from peripheral blood mononuclear cells. Lab Invest. 2002 Sep;82(9):1183-92.] [Schmidt M, Sun G, Stacey MA, Mori L, Mattoli S. Identification of circulating fibrocytes as precursors of bronchial myofibroblasts in asthma. J Immunol. 2003 Jul 1;171(1):380-9. ] [Moore BB, Kolodsick JE, Thannickal VJ, Cooke K, Moore TA, Hogaboam C, Wilke CA, Toews GB. CCR2-mediated recruitment of fibrocytes to the alveolar space after fibrotic injury. Am J Pathol. 2005 Mar;166(3):675-84. ]

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