Learning Objectives: By the end of this lesson, students should be able to describe the organization and purpose of the immune system, differentiate innate and adaptive immunity, and explain how the body recognizes and eliminates pathogens and abnormal or damaged cells.
Introduction
The immune system is a complex network of cells, tissues, and molecules that:
- Recognizes non-self antigens
- Detects and eliminates diseased, damaged, or dying cells
- Maintains tissue homeostasis and defends against infections
It is organized into two complementary arms: innate immunity (rapid, non-specific) and adaptive immunity (specific, memory-driven).
Division of the Immune System
Innate Immunity
Definition: First line of defense; fast, non-specific
- Key Components:
- Physical barriers: skin, mucosa
- Phagocytes: macrophages, neutrophils
- Natural Killer (NK) cells
- Complement system
- Pattern Recognition Receptors (PRRs): Toll-like receptors (TLRs)
- Function: Provides immediate defense, triggers inflammation, and activates adaptive immunity
Adaptive Immunity
- Definition: Specific defense with long-term memory
- Key Components:
- B lymphocytes: produce antibodies
- T lymphocytes: cytotoxic (CD8+) and helper (CD4+)
- Function: Recognizes specific antigens, develops immunological memory, and coordinates with innate immunity
Key Functions of the Immune System
| Function | Description |
|---|---|
| Pathogen Elimination | Detects and destroys bacteria, viruses, fungi, and parasites |
| Surveillance of Abnormal Cells | Eliminates transformed or stressed cells to prevent tumors |
| Tissue Repair | Removes dead or damaged cells to promote healing |
| Immune Regulation | Maintains tolerance to self-tissues to prevent autoimmunity |
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