What are the Chemical Mediators of Inflammation?

The mediators of inflammation are the substances that initiate and regulate inflammatory reactions. Many mediators have been identified and targeted therapeutically to limit inflammation.

Principal Mediators of Inflammation:

Histamine  Source: (Mast cells, basophils, platelets)  Action: Vasodilation, increased vascular permeability, endothelial activation

Prostaglandins   Source:Mast cells, leukocytes  Action: Vasodilation, pain, fever

Leukotrienes  Source: Mast cells, leukocytes  Action: Increased vascular permeability, chemotaxis, leukocyte adhesion, and activation

Cytokines (TNF, IL-1, IL-6)  Source: Macrophages, endothelial cells, mast cells
 Action: Local: endothelial activation (expression of adhesion molecules). Systemic: fever, metabolic
abnormalities, hypotension (shock)

Chemokines  Source:Leukocytes, activated macrophages   Action: Chemotaxis, leukocyte activation

Platelet-activating factor  Source: Leukocytes, mast cells  Action: Vasodilation, increased vascular permeability, leukocyte adhesion, chemotaxis, degranulation, oxidative burst.

Complement  Source:Plasma (produced in liver)  Action: Leukocyte chemotaxis and activation, direct target killing (membrane attack complex), vasodilation (mast cell stimulation)

Kinins  Source:Plasma (produced in liver)  Action: Increased vascular permeability, smooth muscle contraction, vasodilation, pain

What is chemotaxis?

After exiting the circulation, leukocytes move in the tissues toward the site of injury by a process called chemotaxis, which is defined as locomotion along a chemical gradient. 

Both exogenous and endogenous substances can act as chemoattractants. 

Exogenous agents are bacterial products, including peptides that possess an N-formylmethionine terminal amino acid and some lipids. 

Endogenous chemoattractants include several chemical mediators 

(1) Cytokines, particularly those of the chemokine family

(2) Components of the complement system, particularly C5a

(3) Arachidonic acid (AA) metabolites, mainly leukotriene B4.