Which component is NOT an anaphylatoxin?

Anaphylatoxins are small peptides that are generated during the complement activation process and play a crucial role in the inflammatory response. They are particularly known for their ability to induce mast cell degranulation, leading to the release of histamine and other mediators that contribute to acute inflammation and allergy symptoms.

C3a and C5a are well-established anaphylatoxins, as they have been shown to promote various immune responses such as chemotaxis of immune cells, increased vascular permeability, and stimulation of mast cells. Their functions make them integral to the inflammatory response and in the context of allergic reactions.

C4b, while part of the complement cascade, does not possess the same biological activity associated with anaphylatoxins. Instead, it plays a role in opsonization, helping to target pathogens for destruction by phagocytes, rather than modulating inflammation or inducing mast cell activation.

C5b, on the other hand, is specifically not an anaphylatoxin. Instead, it serves as a component that initiates the assembly of the membrane attack complex (MAC), which is responsible for lysing pathogens. Its primary function is to aid in the direct killing of microbes rather than contributing to anaphylactic or inflammatory responses