What is Immunity?
Immunity is the body’s ability to defend itself against harmful invaders like bacteria, viruses, parasites, and even cancer cells.
It’s our natural defense system — a complex network of cells, tissues, and organs that work together to detect, fight, and remember threats.
In simple words:
Immunity = protection. It helps your body stay alive and healthy in a world full of invisible dangers.
Two Main Types of Immunity
This protection system is divided into two main types based on how they work:
1. Innate Immunity (the first line of defense)
2. Adaptive Immunity (the specialized, learned response)
They work together: When innate immunity is unable to fully stop the invader, the adaptive immune system steps in to help fight and protect the body more effectively.
This teamwork creates a strong, layered defense system — fast and general at first, then highly targeted and powerful when needed.
1. Innate Immunity – Fast but General
This is the immediate response your body uses the moment something foreign enters. It doesn’t need training. It’s inborn, meaning you’re born with it.
Key Features:
• Fast (acts within minutes or hours)
• Non-specific (attacks anything unfamiliar)
• No memory (it doesn’t improve with repeated exposure)
🔬 Examples of Innate Immunity:
1. Physical Barriers
• Skin – blocks pathogens from entering
• Mucous membranes – trap microbes in the nose, lungs, and digestive tract
• Cilia – sweep out dust and microbes from the airways
These are like the walls and gates of your body’s fortress.
2. Chemical Barriers
• Stomach acid (HCl) – kills bacteria in food
• Enzymes in saliva and tears – break down bacterial cell walls
• Lysozymes – destroy microbes in secretions
These act like chemical weapons that dissolve invaders.
3. Cellular Defenses
• Neutrophils – first responders that engulf bacteria
• Macrophages – big eaters that also signal other immune cells
• Natural Killer (NK) cells – destroy virus-infected and abnormal cells
These are your immune system’s foot soldiers and snipers.
4. Inflammation
• Increases blood flow and immune cell access to infected areas
• Causes redness, swelling, and pain as a call to action
Inflammation is the body’s alarm system — bringing help to the fight.
2. Adaptive Immunity – Slow but Specific
This is the second line of defense, and it’s much smarter.
Adaptive immunity takes time to respond, but when it does, it targets the invader with precision and remembers it for the future.
Key Features:
• Slower to activate (takes days)
• Highly specific (targets unique pathogens)
• Has memory (responds faster on repeat exposure)
Key Players:
• B cells – produce antibodies that recognize specific pathogens
• T cells – destroy infected cells and help regulate the immune response