Antigen vs Pathogen – What is the Difference?
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Pathogen –
We all might have experienced falling sick such as having fever or infection. In very simple term if I put it, the organism which has the ability to make us sick is called pathogen. An organism that can cause disease is called pathogen. Pathogens can be bacteria, viruses, fungi and even protozoa. Pathogens are foreign organisms which mean they are different than bacteria found in our body or on our skin (normal flora). Normal flora is friendly bacteria but pathogens are not, pathogens invade our body and cause disease.
When pathogen enters our body we would expect our immune system to fight against it. But do you know that our immune system or immune cells cannot recognize pathogen as whole. What they can recognize is a specific part (molecule) of a pathogen present on its surface. These specific molecules present on surface of pathogen and recognized by immune system is called antigen.
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Antigen – Antibody generator
Antigen means Antibody generator. It is a molecule located on the cell wall of bacteria or on coat of virus or on any other organism. Antigens are generally proteins but they can also be polysaccharides, nucleic acid or lipids.
These antigens present on pathogens are very specific for that particular pathogen. Such as an Ag present on Mycobacterium tuberculosis is unique to it and is different than an Ag present on Salmonella.
One more important thing to know about Ag is that the term Ag is not restricted to these surface molecules only. An Ag can be any foreign molecule which triggers immune response in our body. Such as MHC molecule from a different individual in organ transplant, some protein in food, component of serum etc.
So the major difference over here that we need to understand is Pathogen is a whole organism which causes the disease but Ag is part of this organism which is actually recognized by our immune system.
Figure – Difference between Antigen and Pathogen
I hope this post helps 🙂
To understand more details, watch a video on this topic here.