Blunted IL-7 response of pro-B cells derived from young and aged My-bi HSCs. BM cells from young (A) or aged (B) D2 or B6 mice were cultured in 10 ng/mL IL-7 for 1 week. BM cells from hosts, clonally repopulated by individual My-bi HSCs (C), were cultured in the same way. The data are expressed as mean percentage recovery of donor-type cells after culture (± SD). The number (n) of independent experiments performed is indicated at the bottom.