Effect of Batf2 deficiency on gene epxression in murine alveolar macrophages treated ex vivo with IFNg and K. pneumoniae supernatant
Basic leucine zipper transcription factor ATF-like 2 (BATF2) is a transcription factor that is emerging as an important regulator of the innate immune system. We previously identified BATF2 among the top upregulated genes in human alveolar macrophages treated with LPS, but the signaling pathways that induce BATF2 expression in response to Gram-negative stimuli are incompletely understood. In addition, the role of BATF2 in the host response to pulmonary infection with a Gram-negative pathogen like Klebsiella pneumoniae (Kp) is not known. We show that induction of Batf2 gene expression in macrophages in response to Kp in vitro requires TRIF and type I interferon (IFN) signaling, but not MyD88 signaling. Analysis of the impact of BATF2-deficiency on macrophage effector functions in vitro showed that BATF2 does not directly impact macrophage phagocytic uptake and intracellular killing of Kp. However, BATF2 markedly enhanced macrophage pro-inflammatory gene expression and Kp-induced cytokine responses. In vivo, we observed that Batf2 gene expression was elevated in the lung tissue of wild type (WT) mice 24 h after pulmonary Kp infection, and Kp-infected BATF2-deficient (Batf2-/-) mice displayed a modest but significant increase in bacterial burden in the lung, spleen and liver compared to WT mice. WT and Batf2-/- mice showed similar recruitment of leukocytes following infection, but in line with our in vitro observations, pro-inflammatory cytokine levels in the alveolar space were reduced in Batf2-/- mice. Altogether, these results suggest that BATF2 enhances pro-inflammatory cytokine responses in macrophages in response to Kp, and that as such, BATF2 contributes to the host defense against pulmonary Kp infection. Overall design: To investigate the impact of BATF2 on macrophage polarization, we obtained murine WT (C57BL/6J) and Batf2-/-  alvaolar macrophages and treated these ex vivo with IFNg (10 ng/mL) for 4 hours, followed by stimulation with 20% K. pneumoniae supernatant for 6 hours to induce M1-like macrophage polarization We then performed gene expression profiling using data obtained from bulk mRNA-sequencing of 4 WT and 4 Batf2-/- alveolar macrophage samples Each sample represents a biological replicate created by pooling alveolar macrophages from 4 individual mice (N=16 WT and N=16 Batf2-/- mice used in total for the experiment).