Which pathway activates the complement system when a macrophage ingests a microbe, triggering the liver to produce lectin?

• A. Classical pathway
• B. Alternative pathway
• C. Lectin pathway
• D. Adaptive immunity pathway

Answer: (C)

The correct answer is the lectin pathway, which is a key component of the innate immune response. This pathway is specifically activated when lectins, a type of protein that binds carbohydrates, recognize and attach to specific sugars on the surface of pathogens, such as microbes. When a macrophage engulfs a microbe, it can trigger the production of lectin by the liver. The binding of lectin to these sugars initiates a cascade that activates the complement system, enhancing the ability to clear pathogens from the body.

Understanding this pathway highlights the innate immune system's role in providing an immediate response to infection, distinguishing it from the classical and alternative pathways, which activate the complement system through different mechanisms. In particular, the lectin pathway showcases how the body can utilize molecular recognition of foreign invaders to mount an effective defense.