Human MSC-mediated activation of influenza matrix protein 1-specific T-T hybridomas. (A) Bone marrow-derived DR1-positive human MSCs were treated or not for 24 hours with recombinant human IFNγ (100 ng/mL) and subsequently cocultured for 24 hours with influenza matrix protein 1-specific DR1-restricted T-cell hybridomas with or without 100 μg/mL purified influenza matrix protein 1. Supernatant was collected and tested for IL-2 release by ELISA. Means of duplicates ± standard deviations of 1 of 2 representative experiments are shown. (B) Human MSCs were analyzed by flow cytometry for B7-H1 surface expression before and after recombinant IFNγ treatment (100 ng/mL for 24 hours). Plots show isotype control IgG staining profile (broken line) versus specific Ab staining profile (dark line).