Innate & Adaptive Immunity: Definitions & Differences

Instructor: Darla Reed

Darla has taught undergraduate Enzyme Kinetics and has a doctorate in Basic Medical Science

In this lesson you will discover what innate and adaptive immunity are. You will also learn the difference between the two types of immunity and the types of cells involved.

What is Innate Immunity?

How do you know how to breathe? No one taught you. You were born knowing how to do it. Breathing is innate- it's something that is inborn.

Immunity means 'protected from'. Someone who is immune to bullets can't be hurt by them (like superman). When it comes to your body, there is a system that protects you, not from bullets, but from disease. This system is the immune system.

The immune system protects you from disease.
The immune system protects you from disease.

Innate immunity therefore is the inborn or natural protection from disease. This is the first line of defense for the immune system. All animals have some form of innate immunity. There are all kinds of foreign invaders (viruses, bacteria, parasites), also called pathogens, just waiting to attack and take over your cells. To do so, they're going to have to get past your innate immunity first.

How does the innate immune system distinguish a pathogen from its own cells? Think of how you know who's on your team when you're playing sports. Usually, everyone on your team has a particular color or uniform that they wear. If you're wearing red and a person wearing blue has the ball, you know the person isn't on your team.

Similarly, pathogens often have a different 'shirt color' than your own cells. The 'shirt color' is called a pathogen-associated molecular pattern (PAMP). The innate immunity recognizes this PAMP and immediately begins its assault.

Innate immunity recognizes PAMPs
Innate immunity recognizes PAMP

Pathogens may be inactivated (stopped in their tracks), killed, or even eaten (yes, eaten!) by the components of innate immunity.

Components of Innate Immunity

There are many components that make up the innate immunity. One component is your skin. Another is a group of proteins called complement that recognize, attach to, and attack an invader.

Have you ever watched ants as they swarm around an invader? The complement system is like ants that have found an invader. One protein signals to another, which attracts another and so on, until they are all gathered and begin to attack the pathogen.

Complement is part of innate immunity.
Complement is part of innate immunity and recognizes pathogens

Proteins are not the only component. Many cells, such as macrophages, neutrophils, dendrites, and natural killer cells (NK cells) are also part of the innate immune system. The cells detect the PAMP and can attack the invader in one of two ways. They may eat the pathogen in a process called phagocytosis or they may poke holes in the invader until it dies (an action called lysis).

Pathogens can be lysed or phagocytosed.
Pathogens can be lysed or phagocytosed

Cells that eat the invader also play a role in adaptive immunity. So what is adaptive immunity?

What is Adaptive Immunity?

Imagine your sports team once again; you're in red jerseys playing against the blue team. What about the person who's subbing into the game and is wearing a white shirt? Just like you might not know what team the person in the white shirt belongs to, many pathogens don't have a PAMP. Also, many pathogens have developed ways to avoid the innate immune system. When this happens, it's the adaptive immunity's turn.

Adaptive Immunity is where the immune system 'adapts' itself to a pathogen. It finds the best way possible to eliminate an invader quickly and efficiently, based on the pathogen's own characteristics.

Adaptive immunity targets specific parts of a pathogen.
Adaptive immunity targets specific parts of a pathogen.

This is the second level of defense the immune system has set up. Not all animals have an adaptive immune system, only vertebrates (animals with a backbone).

Because it discovers and then uses the characteristics of the pathogen against itself, adaptive immunity is highly specific and more powerful in destroying the invader than the innate immunity. But for this reason, it is often slower to respond than the innate immune system.

Adaptive immunity can be active or passive. Active occurs when an invader is present in the body and there are no tools yet to stop it. Passive happens when the tools to fight the pathogen are simply passed on to a person, like though a mother's milk.

Components of Adaptive Immunity

The adaptive immune system is mainly run by B and T cells, although other cells do participate. A set of T-cells, T-helper cells, are like generals in an army. They tell the soldiers where to go and who to attack. The B-cells are like the soldiers. They know which specific pathogens to attack.

T-cells tell other cells what to attack.
T-cells tell other cells what to attack.

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