inflammatory response

Definition

Target type: biologicalprocess

The immediate defensive reaction (by vertebrate tissue) to infection or injury caused by chemical or physical agents. The process is characterized by local vasodilation, extravasation of plasma into intercellular spaces and accumulation of white blood cells and macrophages. [GO_REF:0000022, ISBN:0198506732]

The inflammatory response is a complex biological process that occurs in response to tissue injury, infection, or other harmful stimuli. It involves a series of coordinated events that aim to eliminate the cause of injury, remove damaged tissue, and initiate repair processes. Here's a detailed breakdown of the key stages and mechanisms involved:

**1. Recognition of Injury or Infection:**
- **Pattern Recognition Receptors (PRRs):** Immune cells express PRRs that recognize molecular patterns associated with pathogens (e.g., bacteria, viruses) or tissue damage (e.g., damaged cells, extracellular matrix components). These patterns are known as pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs).
- **Complement System:** The complement system is a cascade of proteins that is activated when it encounters pathogens or damaged cells. This activation generates various products that can directly kill pathogens or activate immune cells.

**2. Vasodilation and Increased Vascular Permeability:**
- **Histamine and other Vasoactive Mediators:** Immune cells, such as mast cells, release histamine, prostaglandins, and other vasoactive mediators. These substances cause blood vessels to dilate (vasodilation), increasing blood flow to the injured area. They also increase vascular permeability, allowing fluid and immune cells to leak out of the blood vessels into the tissues.
- **Increased Blood Flow:** Increased blood flow brings more immune cells, oxygen, and nutrients to the site of injury.

**3. Recruitment of Immune Cells:**
- **Chemotaxis:** The release of chemokines, small signaling molecules, attracts immune cells to the site of injury. Neutrophils, macrophages, and other immune cells migrate along the concentration gradient of chemokines.
- **Margination and Diapedesis:** Neutrophils and other leukocytes adhere to the endothelium (lining of blood vessels) and then squeeze between endothelial cells (diapedesis) to enter the tissues.

**4. Phagocytosis and Clearance of Pathogens and Debris:**
- **Neutrophils:** These are the first responders to infection and injury. They engulf and destroy pathogens through phagocytosis, a process of engulfing and digesting foreign material.
- **Macrophages:** These cells arrive later and play a crucial role in cleaning up the site of inflammation. They engulf cellular debris, pathogens, and other foreign material, and they release factors that promote tissue repair.

**5. Tissue Repair and Regeneration:**
- **Growth Factors:** Macrophages release growth factors that stimulate the proliferation and differentiation of cells involved in tissue repair. This process includes fibroblasts that produce collagen and other extracellular matrix proteins to rebuild the damaged tissue.
- **Angiogenesis:** New blood vessels are formed (angiogenesis) to provide oxygen and nutrients to the healing tissues.

**6. Resolution of Inflammation:**
- **Anti-inflammatory Signals:** As the inflammation subsides, anti-inflammatory mediators are released, such as interleukin-10 (IL-10). These mediators help to resolve the inflammatory response and promote tissue repair.
- **Apoptosis of Immune Cells:** Many of the immune cells involved in the inflammatory response undergo programmed cell death (apoptosis) to prevent excessive inflammation.

**Overall, the inflammatory response is a crucial defense mechanism that helps to protect the body from infection and injury. It is a tightly regulated process that involves a complex interplay of immune cells, signaling molecules, and other mediators.**
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