Nib asked, and Nib — askNib's tutor — drew the answer live at a whiteboard. This is the spoken transcript; enable JavaScript to watch it drawn.
how does the immune system fight viruses
A virus can't do anything alone. It docks on one of your cells and slips inside, because it needs the cell's machinery to copy itself.
Inside, the virus turns the cell into a copy factory. Within hours one virus becomes hundreds, which burst out and infect neighboring cells.
An infected cell can't save itself, but it can warn others. It releases a chemical alarm called interferon, and neighbors that receive it harden their defenses.
Meanwhile macrophages, big cleanup cells, swallow free viruses. The alarm also raises your temperature. Fever slows the virus and speeds your defenders.
The macrophage also shows a scrap of the virus to a helper T cell, the team captain. Helper T cells wake up B cells and killer T cells. The first time, that takes a week or two.
B cells make antibodies, Y-shaped proteins that lock onto free virus. That blocks the virus from docking and tags it for the macrophages to eat.
But antibodies can't reach a virus hiding inside a cell. That job belongs to killer T cells, which find infected cells and destroy them before the new copies burst out.
So, the whole idea: fast general defenders first, then antibodies and killer T cells aimed exactly at this virus. And memory cells stay, so the next meeting is fast.
Your body wins in two waves: quick general defenders, then a trained team that remembers the virus for next time.