Complement-derived protein fragment (e.g., C3a, C4a, or C5a) capable of directly triggering mast celldegranulation, chemotaxis, smooth muscle contraction, and inflammation.
Source: PAC, 2012, 84, 1113. (IUPAC glossary of terms used in immunotoxicology (IUPAC Recommendations 2012)) on page 1122 [Terms] [Paper]