B cell
１．What is a B cell made from?
A B cell and a T cell are made from a hematopoietic stem cell which we explained about in a section “What is a blood?”

hematopoietic stem cell

It is the precursor cell of a B cell, i.e., the B cell which has not ripened yet, that looks like white bubble.

It is the more immature B cell that looks like a round and black cell (botryoid).  
This picture image is a photograph at the time of cultivating the cell of a fetus liver together with other cells in a test tube. The state in the body is not expressed as it is.

It is posted under the permission of Dr. Satoshi Takagi, Research Institute International Medical Center of Japan, regional health- care medical care research department.
２．What is the job of a B cell?
It makes an antibody.
What is the antibody?

When we make a thing which is a foreign substance for oneself, that is not a self an antigen (a counter body for self), the thing counters it is called an antibody.

However, its cell is considered to be an antigen and an antibody may be made.
If we think widely, what is dealt with at an immune system is an antigen, and what counters it is an antibody.
Man can make an antibody at random. In other words, man makes an antibody for the antigen which does not exist in this world.
The one human being already makes and has all antibodies to all antigens and the unknown.

Man has an antibody for an AIDS virus, a new strain of influenza virus before infected.

Although all is considered not to be defeated by a virus, but these are weak antibodies of power.
It will be the immune strength that the weak antibody of power turns into a strong antibody, and the number increases. We often get sick before having the immune strength.
 Don’ take it wrong!
An antibody is not made only after an antigen goes into the inside of the body. The body already has all antibodies.

One immunity cell prepares only one kind of antibody for one kind of antigen.
３．Why can it do such a thing?
Various genes construct and change, and can make a new protein, i.e., an antibody from a new gene in people's immune system

A new gene is born in the immune system of the internal body. Therefore, there is not be the human being same as oneself in the world, isn’t it?
Attention here!
It is thought up until quite recently that the child becomes individual when the child receives genes from both mother and father, and the gene which does not resemble parents among them expresses.

However, it turned out that a gene is newly made from an immune system and new protein is made from it according to it. In other words, a gene is made in the human body regardless of parents’ genes.

Actually identical twins are also respectively different human beings.

There is no person as same as oneself in this world.                                            

Our body is protected by the immune system, and we are given the life, therefore our body is precious, so let’s take great care of it. 
If various antigens are compared to a key, various antibodies, keyholes are made in this site.
The place where the antibodies which amounts to 100 million kinds are made

The shape of the antibody is shown in the left figure. Two antigens are put together.
 

There will the ones like itself, and the same one too in various antigens.
 
An antibody is made for the antigen which resembles the cell of one's body.

４．An antibody is also made to the component of our own body.

Then, man will die. What has become?

Is it all right that this antibody is inside the body?

If the antibody is made for the component of our own body, our body will be disappear.
Then, what should we do? How has the human being been alive without making an antibody for the gradient of own body?
Although the antibody is actually made for the component of own body, the antibody is going to disappear. How does it disappear?

As you see in the animation below, a B cell is made in a bone marrow. When it becomes an immature B cell from a pre B cell, an antibody is made for the various antigens of own body.

There are always many components of own body around the immune cell.
Therefore, most of the antibodies made at this time are the ones made to own body.
An immature cell B reacts and a made antibody disappears.

An immature B cell made in a bone marrow moves to a lymph node or a spleen through a blood stream.

The animation below shows how the antibody is made for it when the component of own body is recognized to be an antigen, and the antibody disappears. These reaction is conducted with an immature B cell, and it finishes with a mature B cell.

It is how an immature B cell gathers in a lymph node and a spleen, and becomes a mature B cell after deleting an antibody made to the component of own body.
A lot of B cells gather in a lymph node.
A cell shown in red is a B cell, and blue one is a T cell.
After a T cell also eliminates an antibody to the component of own body at the thymus gland like a B cell, it gathers in a lymph node and a spleen.

An antibody to own body disappears.
５．What will happen if the antigen which is not itself goes into the body, for example an influenza virus invades?
It is considered as antigens, such as a virus or bacteria.
（１）Since an antigen exists in the blood, it flows into a lymph node.

An antigen goes into the place where a lot of B cells gathered.

（２）A lot of B cells adhere to antigens. Then, the stimulation makes B cells divide and increase in number, and old weak antibodies (IgM) turned into the strong antibodies called IgG.

成熟Ｂ細胞 mature B cell
（３）It would be better if a lot of antibodies are made in the body. A plasma cell does this duty.
As you see in the page of the virus, a dendritic cell reacts to the residue of a protein of the virus, and a helper T cell became active. This helper T cell makes an appearance here.
 
As you see in the upper animation, a helper T cell which became active encourages a B cell, and changes it into a plasma cell.
 
It is advantageous for immunity to increase a plasma cell which makes a lot of antibodies than to increase a B cell with an antibody.
（４）An antibody processes a cell which is not necessary or not good for one’s own body, bacteria.
An antigen adheres to a lot of antibodies and it makes impossible for the antigen to work.
 
In other words, although an antigen adheres to our cells and makes mischief, it becomes impossible.
 
 

The macrophage which appeared in the natural immunity before ate bacteria and a virus, didn’t it?  The antigen which an antibody adhered to, that is bacteria and a virus become easier to eat for a macrophage.
 
 
 
The third way to defeat an antigen. A substance called a complement is doing important work.

The substance named C1 encourages the substances, C5,6,7,8,9.
These are called chain reactions, and start continuously.
 
 

The substance called C5b6789 made last makes a hole in the membrane of the cell.
The surrounding water etc. enter into the cell from the hole, and a cell or bacteria die.

We gave a difficult explanation so far.

Apart from the difficult explanation, what we would like you to know is that it is important to live every day casually.

A cell engaged in the immunity is working constantly in the place which we do not know.
We tend to think that our body is all controlled by the brain since we think and act with head.
In fact, being alive is that every cell is working.
Let’s live through until our cells stop working since we were born as a human being in this world.

The cells of each person live as hard as possible. Please do not take the power that others live for.
（５）Emergence of a memory B cell
Well, a virus invades again, we can make an antibody soon. This means that immunity were acquired.
Why? Because there is a cell with a memory which can make an antibody.

A memory cell is made in the place (germinal center) where a lot of B cells of a lymph node gathered.
 
 

 acquirement of immunity
 
６．Till when will it continue that an antibody defeats a virus?
When a virus was defeated, actually antibodies which increased too many becomes a foreign substance for one’s own body.
When a virus was defeated, actually antibodies which increased too many becomes a foreign substance for one’s own body.It is necessary for the present antibody to disappear at a certain point.
An antibody emerges to a part of an antibody.
The red antibody shown in animation. The site which adheres resembles the form of the original antigen
 
The original antibody which a red antibody does not leave cannot react to an antigen.
The work of an antibody comes to an end.
 
An antibody comes to be made to a certain part of an antibody in a B cell which reacted to an antigen.  It is shown in brown.
 

A B cell which reacted to this will die.

An immune reaction comes to an end.