Expression of PD-L1 and PD-L2 on HBECs regulates CD8 T cell responses. HBECs were first stimulated with IFN-γ and TNF for 24 hours. After three washes, HBECs were incubated either with an isotype control antibody or blocking antibodies specific for PD-L1 and PD-L2, prior to the addition of ex vivo human CD8 T cells labeled with CFSE in the presence of anti-CD3 and anti-CD28. These reagents were left for the entire co-culture period. After 6 days of co-culture, proliferation, IFN-γ and granzyme B were analyzed by flow cytometry. A. Representative dot plots of CD8 T cell responses for 2 different donors: proliferation assessed by CFSE dilution (X axis) vs. IFN-γ (top panel) or granzyme B (bottom panel) production (Y axis). Flow cytometry plots are gated on living CD8 T cells. B-D. Data obtained from 5 CD8 T cell donors on 3 HBECs preparations for proliferation (B), IFN-γ (C) and granzyme B production (D). Student's t-test: * P < 0.05, ** P < 0.01.