By: Prof. Shimon Pollack, Director, Institute of Allergy, Immunology and AIDS, Rambam
Medical Center

The immune system is a complicated network of cells, tissues and organs within the human body.
This network acts with extraordinary coordination to protect the human body from “foreign” invaders, mainly “microbes” (bacteria, viruses, parasites and fungi). When the immune system is impaired and functions at a lower level, this leads to the development of “immune deficiency diseases”, either congenital (in children) or acquired (in adults). Acquired immune deficiency can accompany malignant diseases, and can also be induced by chemotherapy and other treatment modalities that suppress immune functions. One of the frequent and important consequences are the clinical manifestations of excessive occurrence of various infections.

The “foreigners”, the “self” and the “enemies” - who’s who?

The immune system is one of the most complex body systems. It can recognize and remember millions of “enemies” and “attackers”, and in response it can produce and secrete millions of different proteins designed to attack and fight those “enemies”.
The “enemies” are, in most cases, “foreigners” (originating outside the body). However, in certain cases, the immune system attacks cells and proteins of the body itself, thus causing “autoimmune” diseases, such as various types of arthritis, juvenile diabetes and lupus disease.

The millions of cells comprising the immune system, and the millions of molecules secreted by them, are also affected by other body systems (such as, for example, the nervous system and the endocrine system). This influence is reciprocal, because the immune system itself also affects other body systems.
The immune system’s proteins (like all the proteins in the body) are dependent for their construction on building blocks, some of which are supplied only by proper nutrition. Consequently, the normal functioning of the immune system depends on a complex of factors both within the body and outside it, in addition to the central and important role of genes, which are passed on by heredity and control the activity of the immune system.

Vaccines - the system’s reinforcement

If the intact immune system knows how to fight “microbes” so well, why do we need vaccines?
The vaccines prepare the immune system for an expected attack by microbes, thus enabling the system to fight better, more efficiently and more quickly, when the attack occurs. The vaccine is composed of weakened or dead microbes, which are injected into the body and stimulate the immune system, but they do not cause disease, due to their being weakened or dead. This procedure immunizes the person, which means that his immune system already recognizes the specific microbe as it would recognize it if the person would “really” contract the disease. Thus, when a person is immunized and a viral attack arrives, the viruses find the immune system prepared for them and it attacks them immediately. This is in contrast to the situation of a person who is not immunized: his immune system is “surprised” by the attack, and has to contend with the virus from scratch. This process takes time, and meanwhile, the person can develop a disease. In most cases, vaccinations prevent the development of the disease. It must be noted that “naturally” developing infectious disease, especially a viral disease, immunizes the person and he won’t contract the disease again.

When the system is confused

As already mentioned, the key feature of a healthy immune system is its ability to differentiate between the cells and proteins of the body (the “self” components) and the foreign cells and proteins (the “non-self” components), to live in peace with the self and to attack the foreigner.
Substances that can stimulate the immune system to act and to attack are called antigens. An antigen can be part of a virus or a bacteria, or parts of cells from another person who is not an identical twin or a relative. This explains, for example, why transplanted organs (such as a kidney, liver, etc.) are liable to be rejected by the immune system. When the immune system makes a mistake and identifies “self” components as “foreign” components, and, as a result, it attacks the cells and tissues of the body itself - an “autoimmune disease” is developed (as mentioned above).

There are other forms of erroneous and excessive activity of the immune system, where it acts against harmless foreign substances, such as tree pollen or house dust mites. As a result, allergic diseases develop, and the substance against which the immune response develops is called an allergen.

Everything is connected

Due to the close reciprocal relationships and the mutual influence existing between the immune system and other systems of the body, damage to one of the systems can affect the other systems as well. It is well known, for example, that the nervous system and the immune system are interconnected in a number of ways. Under mental stress conditions, messages are sent from the brain to the adrenal glands. In response, the adrenal glands secrete hormones, called “stress hormones”. These hormones are liable, among other things, to weaken and suppress the protective response of the antibodies and cells of the immune systems, and as a result, the body is more exposed to diseases.

The brain, too, is capable of directly sending messages to the cells and tissues of the immune system, through the nerve fibers connected to them. Thus, a good sleep or, alternatively, lack of sleep, can affect the functioning of the immune system. Some studies show that lack of sleep weakens the protective immune responses, and can, therefore, expose the body to diseases, especially infectious diseases. Good and sufficient sleep reduces stress, thus reducing all the pathophysiological results stemming from increased stress. In addition, it induces a more balanced secretion of the immune system’s inflammatory mediators, whose faulty secretion is liable to interfere with normal immune activity.
The immune system plays an important role in the initial protection of the body against the development of cancer. The cells of the immune system are constantly on guard, eliminating and destroying every cell in the body that begins to undergo a malignant change. However, when the immune system is weakened, or when the rate of the malignant change of the cells increases a great deal, the immune system fails to perform its duties properly, and the cancerous process wins.