Stromal markers


I have been too quick with my delete button but this is in response to the recent query regarding markers to differentiate pre-adipocytes from other stromal cells. I have been immunohistochemically dissecting human fibrohistiocytic and fatty tumors for a few years and this is what I believe.
Regarding fibroblasts, for normal, resting, non-reactive fibroblasts,  CD34 is the marker. CD34 stains ubiquitous interstitial undifferentiated fibroblast-like cells in fibrous and fibroadipose connective tissue and a whole family of their neoplasms. From studies on spindle cell, pleomorphic and myxoid lipomas and well differentiated liposarcoma and dedifferentiated liposarcomas, I have come to believe that the ubiquitous CD34+ dendritic interstitial fibroblast-like cell is an adipocyte precursor. Whether all or a subset of these cells are adipocyte percursors is unknown. CD34+ fibroblasts are also myofibroblast precursors. These reactive myofibroblasts express smooth muscle actin. In soft tissue tumors, myofibroblasts often  retain CD34 expression. CD34+ interstital cells also give rise to collagen producing fibrocytes which are positive for vimentin and procollagen type 1.
Other stromal cells, also part of the microvascular unit, take part in tissue remodelling. Factor XIIIa is a marker for dendritic stromal histiocytes that accumulate greatly during tissue remodelling and tumor formation. Factor XIIIa produced by these histiocytes ("tissue cells") helps to orchestrate tissue remodelling controlling  many aspects of  the spreading, adhesion, cytoskeletal  makeup of fibroblasts and endothelial cells (and probably developing adipocytes)  and transglutaminase FXIIIa stabilizes many different matrix proteins (collagens, fibrin, fibronectin) by cross linking them homo- and heterotypically. The FXIIIa positive denrtic histiocytes also differentiate further into phagocytic macrophages that tend to lose FXIIIa expression as they acquire lysosomal CD68 expression indicating phagocytic ability.  Mast cells, also showing dendritic morphology, have many functions, including modulating the biologic activity of the above described FXIIIa+ histiocytes.  Mast cells can be stained using the KP1 clone of CD68, mast cell tryptase,  and of course CD117 (c-kit).
I know that there are many varied genetic markers for genes involved in various stages of adipocyte development. I wonder how many of these can be colocalized to CD34+ dendritic cells in adipose and fibrous connective tissue.
References on request.
Jeffrey S. Silverman HT HTL QIHC (ASCP)
Pathologists' Assistant
Southside Hospital
Bay Shore New York USA

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