Our Immune System is able to detect germs and other foreign material that enters the body, and destroy it. It is able to recognize them as a substance that’s not part of the body itself. We can think of our immunity in two broad categories; the scientific terms used are 1) Innate Immunity; and 2) Adaptive Immunity.
Innate Immunity goes to work immediately. It involves certain white blood cells which can recognize a germ as foreign, attach to it, and destroy it. Innate Immunity also involves skin cells, all sorts of proteins, and mucus membrane that lines the eyes, nose, throat, lungs, stomach, and bowel. The process of destroying germs often involves inflammation, which causes symptoms (fever, redness, swelling, etc.) and can injure the body in its own way
Adaptive Immunity takes weeks to act the first time. It involves other white blood cells called Lymphocytes, which can remember a germ. So the next time that germ enters the body, special lymphocytes trigger an enormous immune response, including antibody production, to destroy the germ immediately without us realizing it (that’s what it means to “be immune”).
There are two broad types of Adaptive Immunity: Humoral Immunity and Cell-Mediated Immunity. Humoral Immunity involves antibody production, which is easy to understand and measure. But Cell-Mediated Immunity, when various white blood cells recruit each other to attack germs, may be much more important. For example, with Covid-19, we read a lot about antibodies, but can’t really tell how well Cell-Mediated Immunity is actually contributing.
Sometimes our immune system makes a mistake, interprets part of our body as a germ, and attacks it. See Auto-Immune Disease.
The immune system is extremely complex. All its different parts are able to communicate. This involves countless molecules interacting with each other, on a level too small to even be seen by a microscope. When I begin to think about this enormous complexity, it’s a little like gazing up at the nighttime sky and imagining all the stars & planets in our universe, or pondering the ocean and wondering about its vastness.
So when I hear people talk about how this or that is “good for the immune system,” I laugh to myself. Our immune system holds its own; nothing in the world can be “good for it.” There are plenty of things bad for the immune system, like malnutrition, dehydration, inadequate sleep, smoking, too much alcohol, hypothermia, various medications, and a whole bunch of diseases (see Conditions That May Cause Immunodeficiency). But never buy a tonic, vitamin, or other scam that’s touted as “good for the immune system” (instead of wasting your money, donate to something worthy).