FGF-2 and/or VEGF-A stimulation and the presence of MPDL22 cells up-regulated tube formation of bEnd5 cells. (A) Co-stimulation of FGF-2 and VEGF-A induced tube-like structures of bEnd5 cells at 12 hrs. Tube formation: Results of 1 representative experiment out of 3 separate experiments are shown. Number of tubes: Data represent the mean ± SD of 5 separate experiments. *p < .05, vs. non-stimulation, FGF-2, or VEGF-A alone. **p < .05, vs. anti-VEGF-A treatment. (B) Co-cultures with bEnd5 and MPDL22 with FGF-2 stimulation promoted tube formation at 12 hrs, and treatment with anti-VEGF neutralizing Ab abrogated tube formation of bEnd5 induced by co-culture with MPDL22 and FGF-2 stimulation. Tube formation: Results of 1 representative experiment of 3 separate experiments are shown. Number of tubes: Data represent the mean ± SD of 5 separate experiments. *p < .05, vs. anti-VEGF-A treatment. (C) Cell-to-cell interactions between MPDL22 and bEnd5 promoted VEGF production. Supernatant from 48-hour MPDL22 cells or bEnd5 cells culture, or from MPDL22/bEnd5 co-culture, was collected. The level of VEGF-A in the supernatant was determined by ELISA. Results of 1 representative experiment of 3 separate experiments are shown. The data represent the mean ± SD of triplicate assays. *p < .05, vs. co-culture of MPDL22/ bEnd5 cells without cell-to-cell interaction.