Fibrocyte subsets in the peripheral blood of SSc-ILD patients and normal subjects. Human peripheral blood mononuclear cells (PBMCs) were isolated and analyzed by flow cytometry for CD45, CXCR4 and ColI. Seven patients and seven normal subjects were used in these studies. (A) Note that the number of CD45+/ColI+ and CXCR+/ColI+ cells is higher in SSc-ILD blood than in normal blood. Note that CD45+/ColI+ fibrocytes are much more prevalent than CXCR4+/ColI+ cells. **P < 0.01. *P < 0.05. (B) and (C) Primary data demonstrating that fluorescence levels provided by isotype controls are readily distinguished from fluorescence levels provided by specific antibodies. For FL1 fluorescence, primary antibodies are biotinylated isotype controls (B) and biotinylated rabbit anti-ColI (C). For FL2 fluorescence, antibodies are isotype control phycoerythrin (PE) (B) and anti-CD45 PE monoclonal antibody (C).