Antibody and Antigen

I'm sure the title has been heard often, or a least a little. Now then, I'll explain.

Antigen - This is the agent that causes your body to produce antibody, as shown by the following picture. It is foreign to the body, i.e. from the external enivoment or and thus, antibodies are formed

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Which brings us to.... Antibodies.

Antibodies - A type of immune system-related protein which binds specifically to an antigen. As explain by the following picture:

Each antibody consists of four polypeptides, 2 heavy and 2 light, joined to form a "Y"-shaped molecule, though the amino acid sequence at the tips of both heavy and light chains vary, which determine the different types of antibody that bind to different types of antigen. Perhaps the next picture will make things seem a little clearer.
 

Now, antibodies are classified into 5 major classes, based on the constant reigon and their immune function.

For those would like an even more detailed explanation on this subject may click on the following link. I hope that readers have gained an understanding on this. I know the two terms are confusing, I know I've been confused by it a few times before finally getting it.