Fibrocytes and fibroblasts—Where are we now

Fibroblasts are considered major contributors to the process of fibrogenesis and the progression of matrix deposition and tissue distortion in fibrotic diseases such as Pulmonary Fibrosis. Recent discovery of the fibrocyte, a circulating possible precursor cell to the tissue fibroblast in fibrosis, has raised issues regarding the characterization of fibrocytes with respect to their morphology, growth characteristics in vitro, their biological role in vivo and their potential utility as a biomarker and/ or treatment target in various human diseases. Characterization studies of the fibrocyte continue as does emerging conflicting data concerning the relationship to or with the lung fibroblast. The source of signals that direct the traffic of these cells, as well as their response to therapeutic intervention with newly available drugs, bring new insights to the understanding of this cell type. The identification of exosomes from fibrocytes that can affect resident fibroblast activities suggest mechanisms of their influence on pathogenesis. Moreover, interesting comparisons with other pathologies are emerging involving the influence of circulating mesenchymal precursor cells on tissue responses.