Restoration of capacity to support B lymphopoiesis by OP9-309 cells transfected with periostin. (A) Western blot analysis of OP9-309 and OP9-309P cells reexpressing his-tagged periostin. Blot probed with anti–his Ab and anti–actin Ab (control). (B) Cocultures of murine and rabbit BM with OP9-309 and OP9-309P cells; number of total cells in cocultures is indicated; error bars shown as SEM from a range of 2 samples. (C) Flow cytometric analysis of B220⁺ (murine) and CD79a⁺ (rabbit) cells arising from cocultures (gray histograms indicate cells from OP9-309P cultures; and open histograms, cells from OP9-309 cultures). Similar results were obtained in 3 independent experiments.