Respiratory CAS Practice Exam

Endotoxin from Gram-negative bacteria—specifically the lipid A portion of lipopolysaccharide—triggers severe sepsis. Lipid A sits in the outer membrane and, when released, is recognised by immune cells via TLR4, prompting a strong release of cytokines such as TNF-α, IL-1, and IL-6. This cascade leads to widespread inflammation, vasodilation, increased vascular permeability, and potential progression to septic shock. Other components, like peptidoglycan, teichoic acids, or capsule polysaccharide, play roles in virulence or immune evasion but do not initiate the potent endotoxin-driven inflammatory response seen with lipid A in Gram-negative infections.