Cancer and the Immune System: Adaptive Defense System

Cancer and the Immune System: Adaptive Defense System

 

The Adaptive Defense System
In her infinite wisdom, Mother Nature evolved far more sophisticated and specific responses to pathogenic invasions eons before humans developed complex military systems. The specific immune response involves a repertoire of specialized cells, chemicals, and hormones that work in a highly coordinated fashion to rid the body of these invaders before they get a chance to multiply and cause harm to the body. The mammalian immune system possesses the ability to recognize every molecule—known and unknown—in the universe! This awe-inspiring feat is even more remarkable when we see that in a healthy human being, the extraordinary recognition capabilities of the immune system does not normally lead to an attack on the body itself. That is why in normal circumstances, my immune cells will tend to guard my kidney against pathogenic invasions but they will ferociously attack a kidney from you (a donor) that was being transplanted into me unless, of course, you were my identical twin. The only way around this transplantation hurdle is the administration of strong drugs to suppress my immune system. Immunologists refer to the second part of our defense system as the adaptive immune system because it has the potential to modify itself and adapt to any weapon that the enemy (pathogens) throws at it.

The vast majority of immune cells are created in the bone marrow as stem cells. As they mature into specialized cells, they exit from the bone marrow and circulate in the blood. Some of the immune cells are deployed to most of the tissues in the body. In order to maximize the efficiency of this defense unit, the immune cells produce chemicals and hormones that enable them to communicate with each other, for example, to alert another group of immune cells that there is an ongoing invasion in some distant part of the body. The innate and adaptive arms of the immune system work in synergy to defend the body against pathogenic onslaughts. How do they do that?

Box 1.1: Glossary
Antigen: A substance that is foreign to the body and is capable of eliciting an immune response. Antigens are to immune cells what red cloths are to mad bulls.

Antibody: A blood protein that is produced by white blood cells when the body recognizes that foreign invaders and their associated antigens have trespassed into the body. The job of the antibody is to fight the invading bacteria or viruses by attaching themselves to these invaders. This marks the invaders for destruction.

Lymphocyte [B lymphocyte (cell) and T lymphocyte (cell)]: A type of white blood cell: there are several types of white blood cells including B and T cells. Together, lymphocytes account for up to a quarter of the white blood cell population in the body. The function of a B lymphocyte is to make antibodies in response to a foreign invader or any substance that the body perceives as foreign.

T Cell: T cells can be sub-divided into four categories: killer T cells, helper T cells, memory T cells, and regulatory T cells.

Killer T cell: As the name suggests, the function of a killer T cell is to kill other cells that the body perceives as foreign. The target of killer T cells includes cells infected with bacteria or viruses, cancer cells, and other harmful cells.

Helper T Cell: Type of white blood cell that helps or stimulates B cells to make antibodies as part of the immune response. They also stimulate killer T cells and cells of the innate immune system.

Immune Response: A cascade of mechanisms that the body activates in order to fight off foreign invaders. Examples of foreign invaders may be bacteria, viruses, and cancer cells. The immune response ranges from phagocytosis (where a group of cells called phagocytes swallow up whole cells) through the manufacture of antibodies by B cells to the stimulation of killer T cells by helper T cells.

Immune System: The entire defense system of the body. It involves the lymph glands, spleen, and a plethora of white blood cells. Our immune system fights infection and also causes allergic reactions.

Immunity: To be immune to a disease such as flu refers to the ability of one’s body to resist infection upon exposure to that particular pathogen (the influenza virus, in this particular case). Upon sensing an invasion by bacteria or a virus, the body activates the immune system to fight off the infection. one of the remarkable features of the immune system is that once the body has been exposed to a particular disease, it remembers the encounter. If the disease were to strike again, the immune system deploys the memory cells and these react fast enough to keep the enemy at bay.

Macrophages: A type of white blood cell within the immune system. They can be found in the lymph nodes, throughout the circulatory system, and in almost all tissues where they act as sentinels. Macrophages can swallow up and kill whole cells such as bacteria, viruses, and cancer cells.

Memory cell: A type of white blood cell that remembers an infection so that when the immune system encounters such a pathogen in the future, the response will be much swifter and more effective.

Regulatory T Cell: As part of the immune response, regulatory T cells specialize in telling B cells when to stop making antibodies. They also instruct T cells to call off an assault at the end of an immune reaction.