How does the immune system work?

Indeed, sir, the immune system is a marvel of biological engineering, working tirelessly to defend the body against invaders. When a foreign substance enters the body, such as bacteria or a virus, the immune system springs into action. White blood cells known as lymphocytes, including B cells and T cells, identify these intruders and mount an attack. B cells produce antibodies, which bind to the invaders, while T cells either kill the infected cells directly or assist other immune cells in their efforts. This coordinated response not only eliminates the current threat but also helps the body remember it, so future encounters are met with greater speed and efficiency, a most admirable feat of nature.