Immune System in Human: Types, Components and Functions
What is the Immune System?
The immune system is a network of cells, tissues, organs and molecules that protects the body from pathogens such as bacteria, viruses, fungi and parasites.
Its primary function is to recognize, neutralize and eliminate foreign invaders that may cause disease.
Types of Immunity
The immune system is broadly divided into:
- Innate Immunity
- Adaptive Immunity
Innate Immunity
Innate immunity is the body's first line of defense and provides immediate protection against pathogens.
Characteristics of Innate Immunity
- Non-specific defense mechanism.
- Acts immediately after infection.
- No immunological memory.
- Present from birth.
- Includes physical and chemical barriers.
Adaptive Immunity
Adaptive immunity is the second line of defense and develops after exposure to specific antigens.
Characteristics of Adaptive Immunity
- Highly specific response.
- Possesses memory cells.
- Mediated by B cells and T cells.
- Improves after repeated exposure.
Humoral Immunity
B lymphocytes produce antibodies that circulate in blood and body fluids.
Cell-Mediated Immunity
T lymphocytes destroy infected cells and provide protection against intracellular pathogens.
Difference Between Innate and Adaptive Immunity
| Feature | Innate Immunity | Adaptive Immunity |
|---|---|---|
| Specificity | Non-Specific | Specific |
| Response Time | Immediate | Delayed |
| Memory | Absent | Present |
| Main Cells | Phagocytes | B Cells and T Cells |
Components of Innate Immunity
- External Barriers
- Phagocytes
- Macrophages
- Complement System
External Barriers
- Skin acts as a physical barrier.
- Tears and saliva wash away microbes.
- Mucus traps pathogens.
- Gastric acid destroys microorganisms.
- Normal bacterial flora prevents pathogen growth.
Phagocytes
Phagocytes are specialized immune cells that engulf and destroy pathogens.
Important Phagocytes
- Neutrophils
- Monocytes
- Macrophages
Steps of Phagocytosis
- Recognition and attachment.
- Formation of pseudopodia.
- Engulfment into phagosome.
- Fusion with lysosomes.
- Destruction of pathogen.
Macrophages
Macrophages are large phagocytic cells distributed throughout body tissues.
Locations
- Lungs (Alveolar macrophages)
- Liver (Kupffer cells)
- Brain (Microglia)
- Bone (Osteoclasts)
- Spleen and lymph nodes
Complement System
The complement system consists of more than 20 plasma proteins that work together to destroy pathogens.
Main Functions
- Opsonization
- Inflammation
- Cell lysis
- Immune regulation
Alternative Complement Pathway
Activated directly by microbial surfaces without antibody involvement.
Key Events
- Activation of C3 convertase.
- Formation of C5 convertase.
- Activation of C5–C9 proteins.
- Formation of Membrane Attack Complex (MAC).
- Lysis of pathogen.
Classical Complement Pathway
Activated primarily by antigen-antibody complexes.
Major Proteins
| Protein | Function |
|---|---|
| C1 | Initiates pathway |
| C2 | Complement activation |
| C4 | Complement activation |
| C1 Inhibitor | Regulation |
Cooperation Between Innate and Adaptive Immunity
Innate and adaptive immune systems work together to provide complete protection.
- Innate immunity provides immediate defense.
- Adaptive immunity provides long-term memory.
- Cytokines connect both systems.
- Complement proteins assist antibody functions.
Frequently Asked Questions
What is the immune system?
A defense system that protects the body from pathogens.
What are the two types of immunity?
Innate immunity and adaptive immunity.
Which cells produce antibodies?
B lymphocytes (plasma cells).
What is phagocytosis?
The process of engulfing and destroying pathogens.
What is the complement system?
A group of plasma proteins that help destroy microbes.