Tetanus doesn’t grant immunity if you actually get it and survive. They are soil/intestinal bacteria normally and they don’t grow within you to a high enough number that your immune system can get a good look at them, their toxin is just potent enough that even at low concentrations it kills you.
There are also protist pathogens which express vast quantities of a particular coat protein on their surface such that when you form an adaptive immune response agains them it is almost certainly against that protein—and something like one in 10^9 cell divisions their DNA rearranges such that they start expressing a different coat protein and evade the last immune response that their host managed to raise, resetting back to no immunity.
Tetanus doesn’t grant immunity if you actually get it and survive. They are soil/intestinal bacteria normally and they don’t grow within you to a high enough number that your immune system can get a good look at them, their toxin is just potent enough that even at low concentrations it kills you.
There are also protist pathogens which express vast quantities of a particular coat protein on their surface such that when you form an adaptive immune response agains them it is almost certainly against that protein—and something like one in 10^9 cell divisions their DNA rearranges such that they start expressing a different coat protein and evade the last immune response that their host managed to raise, resetting back to no immunity.
Aha, I knew it!
That’s really interesting, actually.