C3a is a one of the proteins formed by the cleavage of complement component 3; the other is C3b. It stimulates mast cell degranulation, thus triggering an immune response.

C3a plays an important role in chemotaxis

Chemotaxis

Chemotaxis is the phenomenon in which somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. This is important for bacteria to find food by swimming towards the highest concentration of food molecules,...

, though not as important a role as C5a

C5a

C5a is a protein fragment released from complement component C5. In humans, the polypeptide contains 74 amino acids. NMR spectroscopy proved that the molecule is composed of four helices and loops connecting the helices. On the N terminus a short 1.5 turn helix is also present. The longest helix...

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It is also an anaphylatoxin

Anaphylatoxin

Anaphylatoxins, or anaphylotoxins, are fragments that are produced as part of the activation of the complement system.. Complement components C3, C4 and C5 are large glycoproteins that have important functions in the immune response and host defense...

 and the precursor of the important cytokine

Cytokine

Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...

 (adipokine

Adipokine

The adipokines or adipocytokines are cytokines secreted by adipose tissue.Members include:* chemerin* interleukin-6...

) ASP

Acylation stimulating protein

Complement 3 through its interaction with factors B and D generates C3a. In human body, C3a is rapidily cleaved by :carboxypeptidase B or carbxyopeptidase N that remove the carboxyl-terminal :arginine to generate C3adesArg. Thus, most of plasmatic C3a is present in C3adesArg form...

 through its interaction with carboxypeptidase B

Carboxypeptidase B

Carboxypeptidase B is a carboxypeptidase that preferentially acts upon basic amino acids, such as arginine and lysine.-External links:* The MEROPS online database for peptidases and their inhibitors:...

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