OX40 ligand regulates splenic CD8− dendritic cell-induced Th2 responses in vivo

• OX40 ligand (OX40L) is highly expressed on anti-CD40-stimulated CD8− conventional dendritic cells (cDCs).
• OX40L contributes to both the development of Th2 cells and secondary Th2 responses induced by KLH-pulsed CD8− cDCs in vivo.
• OX40–OX40L pathway is also crucial bone marrow-derived DCs-induced Th2 responses in vivo.

In mice, splenic conventional dendritic cells (cDCs) can be separated, based on their expression of CD8α into CD8− and CD8+ cDCs. Although previous experiments demonstrated that injection of antigen (Ag)-pulsed CD8− cDCs into mice induced CD4 T cell differentiation toward Th2 cells, the mechanism involved is unclear. In the current study, we investigated whether OX40 ligand (OX40L) on CD8− cDCs contributes to the induction of Th2 responses by Ag-pulsed CD8− cDCs in vivo, because OX40–OX40L interactions may play a preferential role in Th2 cell development. When unseparated Ag-pulsed OX40L-deficient cDCs were injected into syngeneic BALB/c mice, Th2 cytokine (IL-4, IL-5, and IL-10) production in lymph node cells was significantly reduced. Splenic cDCs were separated to CD8− and CD8+ cDCs. OX40L expression was not observed on freshly isolated CD8− cDCs, but was induced by anti-CD40 mAb stimulation for 24 h. Administration of neutralizing anti-OX40L mAb significantly inhibited IL-4, IL-5, and IL-10 production induced by Ag-pulsed CD8− cDC injection. Moreover, administration of anti-OX40L mAb with Ag-pulsed CD8− cDCs during a secondary response also significantly inhibited Th2 cytokine production. Thus, OX40L on CD8− cDCs physiologically contributes to the development of Th2 cells and secondary Th2 responses induced by Ag-pulsed CD8− cDCs in vivo.