What happens when a group of streptococci stick to cells in your throat and start to make toxins?
Your body fights back by making clones.
The animated video, Fighting Infection by Clonal Selection, from Etsuko Uno and Drew Berry is so good that if I didn't know better, I would almost think it's really capturing clonal selection on film.
What is clonal selection?
We call this process "clonal selection" because only some lucky cells get selected for cloning. These cells have proteins on their surface that are able bind to bits of stuff from bacteria or viruses. We call that stuff "antigens," and if the protein has just the right shape, and it can bind tightly to an antigen, then that lucky cell (B or T) gets a signal, telling it to start dividing and making new cells. Since the new cells are clones of the original cell, we call it "clonal" selection).
It's a fun process to draw, but my drawings aren't nearly as dynamic as this movie.
In the movie, you'll see an animation of Group A strep binding to throat cells, bits of M protein breaking off and making their way to the lymph nodes, and one lucky B cell receiving the magic signal to grow and make clones.