CCAAT-enhancer binding protein delta (C/EBPδ) protects against Klebsiella pneumoniae-induced pulmonary infection: potential role for macrophage migration.

Mounting evidence suggests an important role for CCAAT-enhancer binding protein delta (C/EBPδ) in the acute-phase response after bacterial infection. However, whether C/EBPδ limits pneumonia remains elusive and is the aim of this study. Therefore, bacterial outgrowth, inflammatory responses, inflammatory cell influx, and survival were assessed in wild-type and C/EBPδ(-/-) mice infected with Klebsiella pneumoniae via the airways. We showed that C/EBPδ expression is highly induced in the lung during pulmonary infection and that Klebsiella-induced mortality was significantly increased among C/EBPδ(-/-) mice. Bacterial loads and inflammatory responses were similar in wild-type and C/EBPδ(-/-) mice early during infection, whereas bacterial loads were increased in C/EBPδ(-/-) mice later during infection. Moreover, macrophage numbers were reduced in lungs of C/EBPδ(-/-) mice. In vitro experiments showed that C/EBPδ only slightly affects macrophage function. Our data thus show that C/EBPδ contributes to host defense against Klebsiella-induced pneumonia and suggests that C/EBPδ-dependent macrophage mobilization is a key mechanism.