The cell surface phenotype of primary-cultured stromal cells does not change with age. FACS histograms of the distribution of (A) VCAM-1 and (B) SCF on primary cultured stromal cells. Gates were set to include only live stromal cells based on FSC, SSC, and acLDL uptake. Eleven other less well-characterized monoclonal antibodies against stromal cells were also tested and no differences in either surface intensity or cellular distribution were found with increasing age (data not shown).