Innate Immune System: Functions and Cells
Innate Immune System Overview
The innate immune system provides a non-specific defense against infections. Unlike the adaptive immune system, it doesn’t confer long-term immunity. Found in all plants and animals, it’s considered an ancient defense strategy.
Major Functions in Vertebrates
- Recruitment of immune cells via cytokines.
- Activation of the complement cascade to eliminate pathogens and dead cells.
- Removal of foreign substances by leukocytes.
- Activation of the adaptive immune system through antigen presentation.
Inflammation: The First Response
Inflammation is triggered by chemical release, creating a barrier against infection and aiding tissue recovery. Symptoms include redness, warmth, swelling, pain, and potential dysfunction (functio laesa).
Leukocytes: The Immune Defenders
Leukocytes, or white blood cells (WBCs), move freely to capture debris and microorganisms. They originate from bone marrow stem cells.
Innate Response Leukocytes
Innate response leukocytes include: natural killer (NK) cells, mast cells, eosinophils, basophils, and phagocytes (macrophages, neutrophils, and dendritic cells).
Phagocytes: Cellular Engulfers
Phagocytes engulf pathogens, enclosing them in an endosome that fuses with a lysosome for destruction. They respond to cytokines and remove dead cells.
Macrophages: The “Big Eaters”
Macrophages are large phagocytic leukocytes that move outside blood vessels. They differentiate from monocytes and destroy bacteria through reactive oxygen species and chemokine production.