An important characteristic of an antigen is that it is perceived to be foreign. It triggers the immune system.
An antigen is any external particle, a pollen grain, or a molecular substance that enters our immune system and it does not recognize it.
In order to fight against foreign particles, our immune system produces antibodies to prevent them from causing harmful effects on health.
It can be a bacteria, chemical, pollen, or virus. these bind against T-cells or antibodies and their presence activate our immune system.
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