Which complement component is known as a strong chemotactic factor and an anaphylatoxin?

The complement component known as a strong chemotactic factor and an anaphylatoxin is C5a. C5a is a small peptide generated during the complement activation cascade, specifically from the cleavage of the complement protein C5.

Its role as a chemotactic factor is essential in attracting immune cells, particularly neutrophils and macrophages, to sites of infection or inflammation. This recruitment is crucial for the initiation of an effective immune response. Additionally, C5a functions as an anaphylatoxin, meaning it can induce degranulation of mast cells and basophils and lead to the release of inflammatory mediators such as histamine. This process contributes to increased vascular permeability and smooth muscle contraction, which are hallmarks of inflammatory responses.

Though C3a and C4a also have roles in inflammation and can induce anaphylactic responses, C5a is the most potent in terms of chemotactic activity and anaphylaxis. C3b, on the other hand, primarily functions in opsonization, providing a surface for phagocytes to adhere to and enhancing their ability to clear pathogens.