Which pathway does MBL activate?

The correct response to the question about which pathway MBL (Mannose-Binding Lectin) activates is the lectin pathway. MBL is a type of pattern recognition receptor that plays a critical role in the innate immune system. It binds to specific carbohydrates found on the surface of pathogens, particularly those with mannose residues, which is common in many bacteria and fungi.

Once MBL binds to these carbohydrate structures, it can then activate the lectin pathway of the complement system. This activation occurs via MBL-associated serine proteases (MASPs) that are associated with MBL, leading to the cleavage of complement components and the subsequent amplification of the immune response.

In contrast, the classical pathway is predominantly activated by antibodies that are bound to antigens, while the alternative pathway can be initiated directly on microbial surfaces or through spontaneous hydrolysis of complement protein C3. The humoral pathway is not a formal term typically used in immunology to describe a specific complement activation path and generally refers to the broader immune responses mediated by antibodies rather than a specific mechanism of complement activation.

Thus, understanding the unique role of MBL in activating the lectin pathway emphasizes its significance in bridging innate and adaptive immunity through recognition of pathogen-associated molecular patterns.