Streptococcus pyogenes (I'll call it strep for short) is one of many pathogenic bacteria which are known to colonise the respiratory tract. as a result it causes the disease known as strep throat, and another known as scarlet fever. If you are lucky, it gets confined to the respiratory tract. However, in some cases Strep can spread to other organs, where it can cause a disease known as necrotizing fasciitis.
How and why it suddenly causes this disease is not known, although there is some evidence that it follows from a bruise or contusion. Current hypotheses state that somehow the damage enables strep to colonise.
However, in order for it to colonise these damaged sites, it has to be able to go systemic first without alerting the immune system.
To do this, bacteria like strep secrete proteins and other compounds which attack immune cells, and the communication systems immune cells use in order to co-ordinate their response against the bacteria.
I am going to talk about one specific protein secreted by strep called "Streptococcus pyogenes Cell Envelope Protease". For short, we'll call it SpyCEP. And I'll show how this one virulence factor can have an extraordinary effect on the immune system.