Introduction
The immune system protects the body from infections and diseases. It consists of two main branches: innate immunity and adaptive immunity. Innate immunity is the body’s first line of defense and works quickly. One part of innate immunity involves anatomical and physiological barriers. Antigens, on the other hand, are foreign substances that trigger an immune response. Let’s explore both topics in simple detail.
a) Anatomical and Physiological Barriers of Innate Immunity
These are the first physical and chemical defenses that prevent pathogens (like bacteria, viruses, and fungi) from entering the body. They are present from birth and are always ready to act.
1. Anatomical Barriers
These are physical structures that block the entry of harmful microbes.
- Skin: Acts as a physical wall against microbes. It is dry and tough, making it hard for germs to enter.
- Mucous Membranes: Found in the nose, mouth, lungs, and digestive tract. They trap pathogens in mucus.
- Cilia: Tiny hair-like structures in the respiratory tract that move mucus and trapped particles out of the body.
2. Physiological Barriers
These include chemicals and bodily conditions that destroy or inhibit microbes.
- Stomach Acid (HCl): Kills most bacteria that enter with food.
- Enzymes in Tears and Saliva: Like lysozyme, break down bacterial walls.
- Normal Flora: Good bacteria on skin and in the gut compete with harmful microbes and stop them from growing.
- Body Temperature: Fever slows down the growth of some pathogens.
Conclusion: Anatomical and physiological barriers are crucial for stopping infections before they even start. They act quickly and are always active.
b) Types of Antigen
Antigens are substances that are recognized as foreign by the immune system and trigger an immune response. They are usually proteins or polysaccharides found on the surface of pathogens, but can also be toxins or foreign tissues.
1. Based on Origin
- Exogenous Antigens: Enter the body from outside (e.g., bacteria, viruses, pollen).
- Endogenous Antigens: Formed inside the body, such as virus-infected cells or cancer cells.
- Autoantigens: Normally found in the body, but wrongly targeted in autoimmune diseases.
- Tumor Antigens: Found on cancer cells and may trigger an immune response.
2. Based on Immune Response
- Complete Antigens: Can both bind to immune cells and trigger a response (e.g., most proteins).
- Haptens: Small molecules that cannot trigger an immune response on their own. When attached to a carrier protein, they become antigenic (e.g., penicillin).
3. Based on Specificity
- T-dependent Antigens: Require help from T-cells to activate B-cells.
- T-independent Antigens: Can activate B-cells without T-cell help. Usually large polysaccharides.
Conclusion
The innate immune system protects the body through anatomical and physiological barriers that block or kill microbes. On the other hand, antigens are key to activating the immune system, especially the adaptive immune response. Understanding these basics helps us appreciate how the body defends itself from disease.