Question

There are three known ways to activate the complement system. The difference in activation pathways lies in how they are kick-started. In this activity, you will determine whether the following statements apply to activation of complement by the classical pathway, the alternative pathway, or the lectin pathway.

Drag each statement to the appropriate box, indicating whether the statement applies to activation of complement by the classical pathway, the alternative pathway, or the lectin pathway.

Answer 1

The complement system can be activated through three pathways: the classical pathway (initiated by antibodies), the alternative pathway (spontaneously activated), and the lectin pathway (initiated by acute-phase proteins). All pathways involve the splitting of the C3 protein and culminate in the destruction of pathogens.

Step-by-step explanation:

The complement system is an essential part of the immune response, and it can be activated through three different pathways: the classical pathway, the alternative pathway, and the lectin pathway. Each pathway has a unique initiation method and plays a role in the body's defense against pathogens.

Classical Pathway

The classical pathway is initiated when antibodies attached to the surface of a pathogen cell activate the complement system. This is part of the adaptive immune response, which allows the body to remember and respond more efficiently to pathogens it has encountered before.

Alternative Pathway

The alternative pathway can be activated spontaneously, without the need for antibodies, and is a part of the innate immune response that is always active at a basal level. This pathway involves the spontaneous breakdown of the C3 convertase and is regulated by endogenous proteins to prevent damage to host cells.

Lectin Pathway

The lectin pathway is activated when mannose-binding lectin (MBL), an acute-phase protein, binds to carbohydrates on the surface of the pathogen. This pathway is somewhat a bridge between innate and adaptive immune systems because MBL levels can increase in response to infection.

All pathways converge at the point of C3 protein split, leading to further steps in the complement activation and resulting in opsonization of pathogens, chemotaxis of phagocytic cells, and the formation of the membrane-attack complex (MAC) which can lyse pathogens.