C5a downregulates TLR4 (Toll-Like Receptor) to induce IL-12 family cytokine expression that can play a critical role in amplifying acute lung injury (ALI) and ARDS (Xiang and Fan 2010; Hashimoto et al. 2004; Puneet et al. 2005). The gene discussed is TLR4; the disease is acute respiratory distress syndrome.