SPI1 and serum lipopolysaccharide activity: Our prior work using bone marrow chimeras of NF-κB luciferase reporter mice conditionally expressing Tamoxifen inducible PU.1 protein in macrophages demonstrated that myeloid-specific PU.1 protein is pivotal in regulating NF-κB dependent acute lung inflammation and macrophage TLR4 gene expression during endotoxemia [23].