Dear Dr. Ian,

It all depends on which functional state of fibroblast you wish to study. If
you want an undifferentiated "reserve cell fibroblast", you can stain for
the human progenitor cell antigen CD34. These cells are known as dendritic
interstitial cells and they richly populate collagenous connective tissues-
normal  areolar, dermal, and visceral connective tissues, particularly in
the adventitia of vessels and skin adnexae. If you want an activated more
functional fibroblast, use procollagen (collagen type I) antibody. If you
want to study myofibroblasts, use the 1A4 clone of alpha smooth muscle
actin. It is my theory that the CD34+ cells differentiate into the latter
two types during tissue remodeling and in neoplasia (reprints on request).
Hope this helps. I love to chat about this stuff.
Jeff Silverman HT HTL QIHC (ASCP)