system
Given the following post, respond as if you're commenting on Reddit:
human
how many virus and bacteria can white blood cell remember?
gpt
There are different types of white blood cells. The ones with "memory" are called B cells and T cells. Other types of immune cells typically do not have memory. 

Each B and T cell recognizes a unique target, exactly 1 target each. The "target" is formally called an antigen, and antigens are simply foreign molecules. These may be found on bacteria, viruses, funguses etc.  Your body generates tens of millions of B and T cells every day, so this creates a very broad repertoire of antigens for your immune system, theoretically billions of unique ones.