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Adaptive Immunity

Adaptive Immunity


This lesson will describe adaptive immunity as the body's third line of defense against pathogens.

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Source: Video and Images Created by Amanda Soderlind

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Welcome to this lesson today on adaptive immunity. Today, we will be discussing the process of adaptive immunity. Adaptive immunity is a specific type of immunity. And what I mean by specific type of immunity is that it has cells, which have receptors for specific types of pathogens.

In other types of immunity, cells will basically just attack any type of pathogen regardless of the type. But with adaptive immunity, it's more of a specific type of response. Adaptive immunity is the third line of defense against pathogens.

Our first line of offense is physical barriers, followed by innate immunity, and then adaptive immunity. It's our third line of defense. As I mentioned, it's a specific type of immune response.

In adaptive immunity, we have B cells, T cells, and phagocytes, which fight specific pathogens. T cells-- basically, what T cells are, are cells that kill abnormal cells and help to activate B cells. B cells are a type of cell that help to make antibodies. These two types of cells are both lymphocytes, a type of white blood cell.

Each T and B cell, which I mentioned are lymphocytes, make receptors for one specific type of antigen and attack anything that has that antigen. Antigens are something that's recognized as not normal. Antigens, basically, will elicit an immune response.

Receptors and antigens fit together like a lock and a key. In this analogy, of them fitting together like a lock and a key, the lock would be like the antigen, and the key would be-- oops, I'm sorry. The lock would be the receptor, and the key would be the antigen.

OK, so basically, what this means is that the receptors, they're a folded up protein with a specific shape. If you think of a lock, only certain keys will be able to open that lock. Only a key with the right shape will be able to open that lock.

These receptors-- let's say we have a receptor with a shape like this-- only a key shaped like this would be able to fit inside. If the key was shaped like this, it would not be able to fit. So antigens have this specific shape as well. The receptors and the antigens fit together like locks and keys. And that's how adaptive immunity works. These T cells and B cells have these certain shaped receptors that will go after antigens with a certain shape and then attack and get rid of that antigen.

Within your cells, or on your cells, you have something called MHC markers. These MHC markers basically mark a cell as self. What this does is it allows pathogen fighting cells of the immune system to know which cells to target and which not to target.

If a cell has these MHC markers that mark it as self, these pathogen fighting cells know not to attack these cells. These cells are part of the body and are supposed to be there. Then they'll focus their energy on attacking cells that are supposed to be attacked, or targeted.

Adaptive immunity takes about a week to develop, but it produces memory cells. These memory cells provide long-term memory. Basically, these memory cells come in handy if this person is-- basically, if a person comes in contact with an illness or a disease or a pathogen that they've already had in the past, memory cells will be able to fight that off quicker if they encountered again. Because they've experienced it once and they know what they need to do in order to get rid of it again.

These memory cells allow the body to fight off this pathogen quicker the second time around. It basically produces us with immunity. You become immune to a certain disorder once you've already had it.

There's two types of adaptive immunity-- antibody-mediated immunity, also known as hum oral immunity, and cell--mediated immunity. An antibody is basically an antigen receptor. Antibodies, basically what they do is flag antigens for pickup. They'll flag a certain antigen to be picked up and disposed of.

Cell-mediated immunity is another type of immunity that is a form of adaptive immunity. If we take a look at adaptive immunity, and break it down a little bit, it involves lymphocytes, which are a type of white blood cell. And the lymphocytes that it involves our B cells and T cells.

B cells, remember, are a type of lymphocyte that make antibodies. Certain types of B cells make antibodies, which as I mentioned will help to flag antigens for pickup. B cells are made in the bone marrow.

That's one way you can remember B cells, because b and bone both stand for B. B cells are made in the bone marrow and they play a role in antibody-mediated immunity. B cells play a role in antibody-mediated immunity responses.

Whereas T cells are made in bone marrow as well, but they actually mature in the thymus, which is an organ located at the base of your neck. And it's the location, as I mentioned, where T cells mature. You can remember T cells and thymus both start with t. These T cells are a part of the cell-mediated immunity.

Adaptive immunity is broken into two different types, antibody-mediated and cell-mediated. Antibody-mediated immunity of focuses mostly on B cells producing antibodies. While cell-mediated immunity focuses mostly on T cells, destroying pathogens.

This lesson has been an overview on adaptive immunity.

Terms to Know
Adaptive Immunity

Also known as specific immunity, adaptive immunity is carried out by T & B lymphocytes and reacts to specific antigens of cells; adaptive immunity also produces memory cells to target the same pathogen if we are ever exposed to it again.


Specific protein markers that are created by the immune system for binding and reacting to specific antigens; antibodies are created by B cells during humoral immunity.


A particle that has the potential to stimulate an immune response; antigens are basically the identity marker of cells for the immune system to see.

B cells

Also known as B lymphocytes, B cell carry out a version of specific immunity called humoral immunity. During humoral immunity B cells form into plasma cells that mass produce antibodies to be secreted into our body tissue cavities.

Memory Cells

Memory cells are genetically programmed cells that have gone through an initial exposure to a pathogen/antigen that can coordinate a much more specific and rapid response if we are ever exposed to that same pathogen/antigen.

T cells

Also known as T lymphocytes, T cells carry out a version of specific immunity called cell-mediated immunity or cellular immunity. During cellular immunity the immune response is enhanced by helper T cells and cells are directly attacked by cyotoxic T cells.