Mediators of inflammation and allergy

Mediators of Inflammation and Allergy

Mediators of inflammation and allergy are chemical substances released by cells of the immune system in response to harmful stimuli such as pathogens, damaged cells, or allergens. They play crucial roles in initiating and regulating the body's inflammatory and allergic responses. These mediators can be broadly classified into different categories based on their origin, structure, and function.

1. Histamine

• Source: Released by mast cells, basophils, and platelets.
• Function: Histamine is a primary mediator in allergic reactions and inflammation. It causes vasodilation, increases vascular permeability, and contributes to symptoms like swelling, redness, and itching. In allergic reactions, histamine release is triggered by allergens binding to IgE antibodies on mast cells, leading to allergic symptoms like hay fever and asthma.

2. Cytokines

• Source: Produced by various immune cells, including macrophages, lymphocytes, and mast cells.
• Function: Cytokines are signaling proteins that regulate the immune response. Pro-inflammatory cytokines such as interleukins (IL-1, IL-6) and tumor necrosis factor-alpha (TNF-α) are key drivers of inflammation. They recruit immune cells to the site of infection or injury and promote inflammation. Anti-inflammatory cytokines, like IL-10, help resolve inflammation.

3. Prostaglandins

• Source: Derived from arachidonic acid in the cell membrane.
• Function: Prostaglandins, particularly PGE2, are involved in fever, pain, and vasodilation during inflammation. They are produced by most cells in response to injury and help modulate the inflammatory process by enhancing vascular permeability and increasing sensitivity to pain.

4. Leukotrienes

• Source: Also derived from arachidonic acid, primarily from mast cells and eosinophils.
• Function: Leukotrienes are potent mediators of inflammation and are especially important in allergic responses, such as asthma. They cause bronchoconstriction, increased mucus production, and attract immune cells to the site of inflammation.

5. Bradykinin

• Source: Generated by the kallikrein-kinin system.
• Function: Bradykinin is a powerful vasodilator that increases vascular permeability and stimulates pain receptors. It is involved in producing the pain and swelling seen during inflammation and allergic reactions.

6. Platelet-Activating Factor (PAF)

• Source: Released by various immune cells, including mast cells, neutrophils, and endothelial cells.
• Function: PAF is involved in numerous inflammatory responses, such as platelet aggregation, bronchoconstriction, and increased vascular permeability. It plays a significant role in allergic reactions, particularly in asthma and anaphylaxis.

7. Complement System

• Source: A group of proteins produced in the liver and present in the bloodstream.
• Function: The complement system is activated during inflammation and allergic responses. It enhances the ability of antibodies and phagocytic cells to clear pathogens, promotes inflammation, and aids in the removal of damaged cells.

8. Reactive Oxygen Species (ROS)

• Source: Produced by activated phagocytes (e.g., neutrophils and macrophages).
• Function: ROS are involved in killing pathogens and signaling within the immune response. However, excessive production of ROS can lead to tissue damage during chronic inflammation.

Clinical Implications

Excessive or prolonged release of these mediators can result in chronic inflammation and allergic diseases, such as asthma, eczema, and allergic rhinitis. Therapeutic strategies often focus on targeting these mediators to reduce inflammation and allergic symptoms. Examples include antihistamines, nonsteroidal anti-inflammatory drugs (NSAIDs), corticosteroids, and leukotriene receptor antagonists.

Understanding these mediators helps in the development of treatments for various inflammatory and allergic conditions.