Immune System – Tutorial #5
Most of us at one time or another have taken a shortcut across a wild meadow with its wildflowers and grasses. When we got to the other side we found our wool socks were full of burs. With this image in mind and the use of your imagination, you will learn another way your immune system mounts an attack against invading cancer cells.
In this illustration you are the intruder into the meadow, just as the cancer cells have intruded into your body. Think of the wool socks as antigens (they are something on the surface of your body that mark you as being foreign to that meadow – “not-meadow”). The meadow has attached cockleburs to your antigens (the socks). What the immune system attaches to antigens are called antibodies.
Now use a really vivid imagination for this next part. Suppose as you get to the other side of the meadow you notice a single bee overhead. It happens to be a killer-bee that is attracted to cockleburs. You look again, and there are several killer-bees. Then you notice they have become a swarm, forming a dark cloud. You realize these bees are dividing – one bee becomes two, two becomes four, four becomes eight, and so on. When these bees spot the cockleburs, the attack will be on.
This story is a good illustration of what the immune system does. A hyperactive macrophage, after it has eaten one of the cancer cells, puts pieces of the cancer antigen (the protein shape that is on the surface of the cancer cell) onto its own surface. Then it communicates with the rest of the immune system and orders antibodies custom made to fit the antigen that it has presented on its own surface. These antibiotics are formed at a speed that staggers the mind. Their job is to tag or mark all of the cancer cells that have that same antigen on the surface of their cell.
At the same time the antibodies are being formed, a unique immune cell called the killer T-cell is also being created. These specially designed immune cells, like the killer bees in the illustration, begin to divide. One becomes two, two become four, and on and on and on. These killer T-cells will swarm throughout the body in search of that particular antibody which is attached to a cancer cell. It will then attack that cancer cell.
The main difference between the killer T-cell and the natural killer cell is that the killer T-cell is programmed to attack a specific antigen, and the natural killer cell will attack multiple antigens. When a killer T-cell makes contact, it is as if the killer T-cell gives the cancer cell an order to commit suicide; an order it has no choice but to obey. In response to this order, the nucleus crumbles, causing the cancer cell to collapse. The deflated remains of the cancer cell are then ready to be digested by macrophage cells.
A significant feature of the antibodies and the killer T-cells is the speed at which they can be produced. In the fight against cancer, it’s always a battle of speed and numbers
I chose the cockleburs as an illustration of how the immune system’s antibodies attach themselves to antigens because most of us have experienced the tenacity with which a bur will attach itself to our clothing. It is with that same tenacity, that antibodies attach themselves to antigens. A more accurate description of an antibody connecting to an antigen is that of a “lock and key” arrangement.
The cocklebur has an interesting history. It is the inspiration for Velcro®fasteners. One day in 1948, an amateur Swiss mountaineer and naturalist, George de Mestral, went on a nature walk with his dog through a field of hitchhiking bur plants. When he and his dog returned home they were covered with these burs.
With an intense curiosity, Mestral went to his microscope and inspected one of the many burs stuck to his pants. He saw numerous small hooks that enabled the seed bearing bur to cling so tenaciously to the teeny loops in the fabric of his pants. He raised his head from the microscope and smiled, and thought of designing a unique, two-sided fastener – one side with stiff hooks like the burs and the other side with soft loops like the fabric of his pants. He called his invention Velcro®, a combination of the words velour and crochet (pants).