C5a act as a/an?
**Core Concept**
C5a is a potent anaphylatoxin derived from the complement system, specifically from the cleavage of C5 by C5 convertase. It plays a crucial role in the inflammatory response by promoting chemotaxis, activating leukocytes, and enhancing vascular permeability.
**Why the Correct Answer is Right**
C5a acts as a chemoattractant, drawing neutrophils and other leukocytes to the site of inflammation. This is mediated through its interaction with the C5a receptor (CD88) on the surface of these cells. The binding of C5a to its receptor triggers a signaling cascade that leads to the activation of various cellular processes, including the release of pro-inflammatory cytokines and the expression of adhesion molecules. This facilitates the recruitment of leukocytes to the site of inflammation, contributing to the inflammatory response.
**Why Each Wrong Option is Incorrect**
**Option A:** C5a is not a vasodilator, as it actually contributes to increased vascular permeability and blood flow to the affected area.
**Option B:** C5a does not act as an anticoagulant, as its primary role is to promote inflammation rather than inhibit blood coagulation.
**Option C:** C5a is not a direct inhibitor of complement activation, as it is actually a product of complement activation itself and serves to amplify the inflammatory response.
**Clinical Pearl / High-Yield Fact**
C5a is a potent mediator of the inflammatory response, and its levels can be used as a marker of inflammation in various disease states, including sepsis and rheumatoid arthritis.
**Correct Answer:** C. chemoattractant.