OX40/OX40L axis plays a role in BMMC functions. (A) OX40 expression and CFSE dilution in gated CD45.2 Teffs and CD45.1 Tregs after 72 hours of coculture with BMMCs. (B-C) Proliferation of Teffs (B) and Tregs (C) obtained from WT or Tnfrsf4^−/− mice, alternatively labeled with CFSE, and seeded in different combinations, in the presence or not of BMMCs. Numbers above bars indicate percentage inhibition of Tregs. *P < .05, compared with the corresponding condition in the absence of BMMCs. °P < .05, compared with the corresponding condition in the presence of WT T cells. (D-E) OX40L expression in BMMCs after 24 or 72 hours of culture alone or in the presence of Teffs, Tregs, or both. When indicated, BMMCs received scaled amounts of recombinant IL-6 (rmIL-6, 1, 5, 20, and 50 ng/mL). (E) Mean fluorescence intensity of OX40L staining (relative to isotype staining) in BMMCs. *P < .05, compared with the same condition at 24 hours. Data are from 1 representative of 2 independent experiments.