HAECs promote the regeneration of cells with hematopoietic stem and progenitor phenotypes. (A) Bone marrow cells (BMC) were harvested from the femurs of mice treated with 580 cGy 137Cs whole body irradiation (WBI) and cultured in the absence (−EC, black bars) or presence (+EC, grey bars) of HAEC monolayers (input BMC: 2 × 106 cells). (B) After 7 days in culture, total BMC were counted and (C) HSCs (Linlo, CD150+, Sca-1+, c-Kit+ (CD150+LSK) cells) were identified by FACS. (D) The absolute number of CD150+LSK cells recovered on day 7 from 2 × 106 input BMC is shown. Error bars show SEM of 5 independent experiments.