Maybe it's the mailroom. Now you know what John Smith does. Eventually you find out how the whole company works. Mak, along with many other researchers around the world, is using a similar process to understand how the immune system works. The human immune system is very complicated and the following is just a very simple explanation of one major part.
Macrophages are like garbage collectors.
They get bits of molecules from invaders and present them to T-Cells for identification. Each T-Cell receptor recognizes one short piece of a protein molecule about 8 amino acids long. There are trillions of unique T-Cells in your body. Enough so that you can recognize any foreign molecule that nature throws at you. Killer T-Cells are better at killing viruses.