Lectin pathway

Definition

The lectin pathway is one of the complement activation pathways that helps the immune system identify and eliminate pathogens. This pathway is triggered when lectins, which are proteins that bind to carbohydrates, recognize specific sugar patterns on the surfaces of microbes, leading to a cascade of reactions that activate the complement system. It plays a crucial role in the innate immune response, complementing other pathways like the classical and alternative pathways.

5 Must Know Facts For Your Next Test

1. The lectin pathway does not require antibodies to initiate activation, unlike the classical pathway, making it an important component of innate immunity.
2. Mannose-binding lectin (MBL) is crucial for the lectin pathway as it binds to specific carbohydrate patterns on pathogens, promoting complement activation.
3. The lectin pathway converges with other complement pathways at the level of C3 convertase, leading to a shared amplification of immune responses.
4. Activation through the lectin pathway can enhance opsonization, helping phagocytic cells to more effectively recognize and engulf pathogens.
5. Deficiencies in components of the lectin pathway can lead to increased susceptibility to infections, particularly with encapsulated bacteria.

Review Questions

• How does the lectin pathway differ from the classical and alternative pathways in terms of initiation?
  • The lectin pathway differs from the classical and alternative pathways primarily in its initiation mechanism. The lectin pathway is triggered by mannose-binding lectins recognizing specific carbohydrate patterns on pathogens, which does not require antibodies. In contrast, the classical pathway requires antibodies bound to antigens for activation, while the alternative pathway can be activated by spontaneous hydrolysis of complement component C3 on microbial surfaces.
• Discuss the role of mannose-binding lectin in activating the lectin pathway and its implications for pathogen recognition.
  • Mannose-binding lectin (MBL) plays a critical role in activating the lectin pathway by binding to specific mannose and fucose residues found on the surface of certain pathogens. This binding leads to a conformational change that allows MBL to associate with serine proteases, forming complexes that initiate the complement cascade. The ability of MBL to recognize diverse microbial carbohydrates enhances pathogen recognition and promotes efficient clearance by immune cells.
• Evaluate how deficiencies in the lectin pathway components could impact overall immune function and susceptibility to infections.
  • Deficiencies in components of the lectin pathway, such as mannose-binding lectin or associated serine proteases, can significantly impair immune function. This impairment reduces the efficiency of pathogen recognition and activation of complement, leading to diminished opsonization and inflammatory responses. As a result, individuals with such deficiencies may experience increased susceptibility to infections, especially from encapsulated bacteria that are normally targeted by this complement activation route.

Related terms

Mannose-binding lectin (MBL): A type of lectin that binds to mannose residues on the surface of certain pathogens, initiating the lectin pathway of complement activation.

Complement system: A complex network of proteins that enhances the ability of antibodies and phagocytic cells to clear pathogens from an organism.

C3 convertase: An enzyme complex formed during complement activation that cleaves complement component C3 into C3a and C3b, leading to opsonization and inflammation.