Classical activation of M1 macrophages can take place during injury, infection, or inflammation in vivo or during in vitro experimentation by exposure to bacterial cell wall constituents such as lipopolysaccharide (LPS) as well as pro-inflammatory cytokines such as interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and granulocyte-monocyte colony-stimulating factor (GM-CSF) [30,32]. The gene discussed is TNF; the disease is infection.