What Is Lipopolysaccharide? The Inflammation Switch in Animal Experiments

Starting from the bacterial cell wall

Lipopolysaccharide (LPS) is present in the outer membrane of Gram-negative bacteria and serves as a protective coat between the bacterium and the external environment. In animal experiments, we rarely use live bacteria directly; instead, we use purified lipopolysaccharide to mimic the body's response to bacterial infection. It is not a complete bacterium itself, yet it can trigger the animal immune system to mount a response similar to encountering bacteria.

Why it causes fever and inflammation

There is a class of immune cells in the animal body whose surface receptors can recognize lipopolysaccharide. When lipopolysaccharide enters the body of a mouse or rat, immune cells release a series of signaling substances, such as tumor necrosis factor and interleukins. These signaling substances further trigger elevated body temperature, vasodilation, and leukocyte recruitment, which are what we commonly refer to as fever and inflammation. Because of this characteristic, lipopolysaccharide is widely used to establish fever models, inflammation models, and infection-related models.

Common uses in animal experiments

Establishing systemic inflammatory response models to observe changes in animal body temperature and activity.

Inducing local inflammation for studying the anti-inflammatory effects of drugs.

Combined use with other stimuli to mimic complex infection states.

Evaluating the effects of immunomodulators on inflammatory signaling.

It should be noted that the response intensity to lipopolysaccharide is related to dose, animal strain, and route of administration. Before experiments, pilot studies should be conducted to determine the conditions suitable for one's own research, and fixed values from the literature should not be copied directly.

What beginners need to pay attention to

Lipopolysaccharide solutions generally need to be freshly prepared before use to avoid repeated freeze-thaw cycles affecting activity. The purity of lipopolysaccharide from different sources may vary, and when selecting, attention should be paid to whether it is suitable for animal experiments. Gloves and goggles should be worn during handling to avoid inhalation or skin contact. Although it is not a highly toxic substance, good laboratory practices can reduce unnecessary exposure.

Overall, lipopolysaccharide is like a "key" that can open the inflammatory response pathways in the animal body. Understanding its mechanism of action helps design more reliable animal experiments.