The immune system’s mission is to protect the body against foreign or dangerous invaders. These invaders can be:
- Microorganisms (usually called germs, such as bacteria, viruses or fungi)
- Parasites (such as worms)
- Cancer cells
- Transplanted organs and tissues
In order to defend the body against these invaders, the immune system must be able to distinguish
- What belongs to the body (self)
- What does not belong to the body (exogenous or foreign)
Antigens are substances that the immune system can recognize and that stimulate an immune response.
If the antigens are perceived as dangerous (for example, if they can cause disease), they can stimulate an immune response in the body. Antigens may be located in or on the surface of bacteria, viruses, other microorganisms, parasites or cancer cells. In other cases, they are independent substances, such as food molecules or pollens.
A normal immune response involves the following:
- Recognition of a potentially dangerous foreign antigen
- Activation and mobilization of forces to defend against that antigen
- Attacking that antigen
- Control and termination of the attack
If the immune system does not function properly and confuses endogenous and exogenous substances, it can attack the body’s own tissues, leading to an autoimmune disease such as rheumatoid arthritis, Hashimoto’s thyroiditis or systemic lupus erythematosus (lupus).
An immune system disorder occurs when
- The body generates an immune response against itself (autoimmune disease).
- The body fails to generate an appropriate immune response against invading microorganisms (immune deficiency).
- The body generates an excessive immune response to foreign, often harmless, antigens and damages normal tissues (allergic reaction).
The immunity system is made of many components:
The antibodies (immunoglobulins), which are proteins produced by white blood cells lymphocytes B cells, bind tightly to the antigen of an invader, marking the invader to attack or neutralizing it directly. The body produces thousands of different antibodies. Each of these antibodies is a specific antigen.
Antigens are substances that the immune system can recognize and that stimulate an immune response.
The cells lymphocytes B are white blood cells that produce antibodies specific to the antigen that has stimulated their production.
Basophils are white globule cells that release histamine (a substance involved in allergic reactions) and produce substances that attract other white blood cells (neutrophils and eosinophils) to the site of infection.
Cells are the smallest unit of a living organism, consisting of a nucleus and a cytoplasm surrounded by a membrane.
Chemotaxis is the process by which a chemical substance attracts cells to a particular site.
he complement system consists of a group of proteins involved in a series of reactions (called the complement cascade), aimed at defending the body, for example by killing bacteria and other foreign cells, facilitating the identification and ingestion of foreign cells by macrophages, and attracting macrophages and neutrophils to the site of infection.
The Cytokines include many different proteins secreted by immune cells as well as other cells, acting as messengers of the immune system to help regulate an immune response.
Dendritic cells are derived from white globule cells. They are present in tissues and help T cells recognize foreign antigens.
Eosinophils are white globule cells that kill bacteria and other foreign cells that are too large to ingest and can help immobilize and kill parasites and destroy cancer cells. Eosinophils are also involved in allergic reactions.
lymphocytes T helper cells are white globule cells that help lymphocytes B cells produce antibodies to foreign antigens, help Killer lymphocytes T cells become active, and stimulate macrophages to ingest infected or abnormal cells more efficiently.
The histocompatibility (literally, tissue compatibility) is determined by human leukocyte antigens (self-identifying molecules). Histocompatibility is used to determine whether a transplanted towel or organ will be accepted by the recipients.
stocompatibility is used to determine whether a transplanted towel or organ will be accepted by the recipients. Human leukocyte antigens (HLA) are a group of identifying molecules located on the surface of all cells in a combination that is almost unique for each person, allowing the body to distinguish between endogenous and exogenous substances. This group of identification molecules is also named the major histocompatibility complex.
An immunity complex is an antibody fixed to an antigen. Antibodies are also known as immune globulins.
