Question

2. What are endotoxin ? Describe endotoxin action and it’s pathogenesis
             Include role of fever and the mechanism of fever induction.

Answer 1

Lipopolysaccharide in the outer layer of gram negative bacterial cell wall which acts as pyrogens and induce fever and inflammation as immune response in the infected organism is called endotoxin. Endotoxin can lead to even high level of reaction such as anaphylactic shock and even death in the affected individual.It is called an endotoxin because it is a toxin located inside bacterial cell wall. O-antigen, the Core oligosaccharide and Lipid-A are the three parts of lipopolysaccharide. Among this the O antigen is the outermost part and is recognized by the host cell and the Lipid A part is responsible for the toxicity of the pyrogen.

As the pyrogen enters in our body it triggers the phagocytosis by macrophages and the bacteria with the endotoxin will be trapped inside the macrophages as phagosome. Next step is phagosome fuses with the lysosome and in the lysosome there is so many enzyme which cause the lysis of bacterial cell and this is a very critical step in infection. When lysis happens lipid A part will come in contact with immune cells . All these leads to release of cytokines such as interleukin such as IL1 , IL6,TNF alpha by macrophages. These cytokines will be released to blood and reaches hypothalamus where it stimulates arachidonic acid pathway and stimulates the production of prostaglandins PGE2 and it causes fever.