Fig. 1

Lineage specific markers are maintained in hTERT immortalized HBFCs. a Diagram depicting the cumulative population doublings of CD105⁺ and CD26⁺ HBFCs transduced with empty vector (evHBFC^CD105; open squares and evHBFC^CD26; open triangles) or hTERT (iHBFC^CD105; closed squares and iHBFC^CD26; closed triangles) and recorded between passages 10 (day zero) and 57 (day 412). Whereas iHBFC^CD105 and iHBFC^CD26 continued to proliferate, empty vector controls ceased to expand after around 18 and 24 population doublings, respectively. Also, note that iHBFC^CD26 have an intrinsic growth advantage irrespective of immortalization. b iHBFCs were examined repeatedly for the expression of lineage markers CD105 and CD26 by immunoperoxidase staining (brown), here illustrated for cells in passage 50. Like their primary ancestors, iHBFC^CD105 are CD105^high/CD26^low (left) and iHBFC^CD26 are CD105^low/CD26^high (right). Nuclei are counterstained with hematoxylin (blue) (bar = 50 μm)