Characteristics of the immune system

Immnune system components, types and diseases

What is the immune system?

The immune system consists of a complex network of organs responsible for protecting the body against foreign substances to which they have to destroy.

The immune system protects the body from diseases caused by parasites and infectious agents from outside (fungi, viruses, bacteria) or from the the body itself (tumor cells).

This capability is called adaptive immunity.

In addition, the immune system also has what is called immunological memory which is the ability to develop a stronger defense system against antigens.

So, when the defense system is again confronted with a known organism, is better adapted to eliminate it.

Types of immunity

The immune system consists of three subsystems or barriers:

  • Defensive barrier mechanisms: The first barrier of defense system is a series of elements whose mission is to prevent the entry into the body of foreign elements. They are mechanical barriers that constitute the first line of defense. So, the body is protected with an outer shell, the skin, to prevent foreign elements from entry.

Strange invaders can be destroyed, as it happens with the action of saliva or gastric acid againts the ingested organisms.

They can be expelled outside, as when a foreign body goes into the lungs and is expelled by coughing violently or enters the nose and is expelled through sneezing. The tears of the eyes also play a similar function.

girl with a wound

A wound can be the entry of microbes in the blood. Our natural immunity, made by leukocytes, is designed to destroyed them before they can infect us.

  • Natural immunity: Despite these barriers, many foreign objects manage to get inside. At this point, they have to face the innate immune system, consisting of leukocytes, which are able to recognize them as something strange and kill them.

It is a barrier made up of innate defensive cells. This barrier offers an immediate response to environmental aggressions. It is produced by the human species as a result of adaptation to the attack of infectious agents

The natural immunity works, for example, when a wound is produced. The wound allows the entry of microbes in the blood, leukocytes are responsible for devouring them to prevent our body to be infected.

  • Acquired immunity: Another barrier is constituted by the defense that develops from contact with the elements that the body recognises not to belong to the body itself. This defense is not inherited but, it has been developed as a result of the contact with these strange substantes.

From this contact, the body develops antibodies that will be responsible for eliminating antigens when they return. Antigens are proteins produced mainly by fungi, bacteria and other toxic substances coming from ouside the body. The immune system is able to detect antigens and produce antibodies to destroy them. For each antigen the body produces a specific antibody.

Besides being developed in a natural way, for example, through illness, immunity can be acquired artificially by vaccines.

Many of the diseases considered “childhood diseases” produce this type of immunity. For example, this takes place when someone, sick with measles, develops antibodies that are capable of eliminating virus attacks after they occur. The chickenpox vaccine is made precisely to develop the antibodies necessary for people to not get sick when they come into contact with the infectious agent. Other conditions developing adquired immunity are rubella or measles.

Other diseases generate a temporary immunity, only valid for the type of organism that produced it. Because microorganisms have a great capacity to produce different variations that can mutate to attack the body and infect it again.

This is the case of the flu. A person can develop immunity after an episode of this disease and is much more likely not to fall ill, but the flu virus mutates very easily from year to year and can easily infect the same patient again when it reappears. That is why flu vaccines provide protection only for a season.

  • Passive immunity: It is a short term immunity which is also called “temporary immunity” as the one provided by the mother’s milk to the nursing baby.

Immune system components

The main components of the immune system are:

  • White blood cells or leukocytes: They are the primary defensive cells. There are two types of white blood cells: phagocytes and lymphocytes.
    • Phagocytes are cells that devour foreign organisms. Within these, the most common are granulocytes, consisting of neutrophils, basophils, and eosinophils.
      • Neutrophils are the most abundant and the first responders to infection. They phagocytize, that ‘s to say, they “eat” invading organisms killing them. When a wound is done, the pus that is formed is primarily made from neutrophils.
      • Other groups of phagocytes are monocytes and macrophages. Macrophages respond more slowly than neutrophils but are larger, live longer and are more capable. In addition to personally kill the invaders, macrophages alert the rest of the immune system of foreign elements in the body.
      • Monocytes are large white blood cells. Its function is to “eat” foreign bodies. They have little time as they become macrophages after 24 hours.
      • Finally, another important group of phagocytes are dendritic cells. Like the rest of phagocytes, they are able to devour any invader. They can inform the rest of the immune system of the presence of foreign bodies and purify fluids.

        man with flue

        Flu can be prevented by applying a flu vaccine. This is aimed to develop antibodies that will recognise the flu virus when entering the body.

    • Lymphocytes: Lymphocytes are cells that originate in the bone marrow but move to different parts of the lymphatic system, such as the spleen, thymus or lymph nodes.

      They are a special type of white blood cells that constitute the defensive cells of the acquired immune system. There are two types: B Lymphocytes and T lymphocytes.

      • B lymphocytes can recognize strange substances and mark them so they can be eliminated. They are extremely useful because they are the ones that produce antibodies, also called immunoglobulins.Antibodies are proteins that attach to antigens and recognize them as foreign to the body. In addition, B cells, upon contact with antigens, are able to create a memory of each one of them.

      Speciall receptors in the lymphocyte surface are able to recognize antibodies. The receivers are very specialized, since they can only recognize a single antigen. There are so many receivers as antigens.

      Thus, when one of these antigens comes back again to invade the body, there is a rapid production of antibodies that will allow the defensive system act quickly.


    The application of vaccines responds precisely to the creation of antibodies. Vaccination is introduced through a weakened body so as to create antibodies. We can say that a flu vaccine, for example, contains the flu virus “weakened” so that the body can make antibodies that recognize the “normal” influenza virus when it enters the body. This recognition will allow a rapid response so that the infection can be removed before it progresses.

    The role of antibodies is not to eliminate but recognize antigens and indicate to other components that must be destroyed. Those who exercise this function are the phagocytes, T cells and proteins called complement group.

    • T lymphocytes or T cells , in addition to recognizing strange substances for the body , collaborate with phagocytes in their elimination

    There are essentially two types: T helper cells or T lymphocytes “natural killers “ (NKT cells).

    • The main function of T helper cells is to activate B lymphocytes and natural killer cells. This is activated by receptors in their outer covering that recognize the presence of invaders through the marks they leave on the surface of phagocytes.
    • Natural killer cells (NTK cells ) are able to recognize and kill cells infected by viruses and bacteria and cancer cells.
  • Complement group proteins: A group of proteins also involved in the elimination of antigens. They are found in the blood and act quickly when an infection.Its function is to produce inflammation in the area (more blood accumulation and, therefore, more defensive cells presence), to inform macrophages about foreing substances, to surround invaders waiting for phagocytes to devour them, or to delete them personally.
  • Lymphatic system: In addition to drain excessive fluids from the body, the lymphatic system is the main component of the immune system.The flow channels are known as lymph vessels and the extensions are called lymph vessels. Lymph nodes are beanshaped clusters formed and distributed in parts of the body such as armpits, neck, or groins.

In the lymph nodes body liquids are purified and absorbed. Furthermore, in lymph nodes lymphocytes are stored. When microorganisms invade the lymph, or when abnormal cells or foreign objects are recognized, the lymph nodes produce more white blood cells to be able to fight infection and remove foreign objects. (More information on lymphatic system)

Diseases or disorders of the immune system

A strong immune system can guarantee immunity against many diseases. However, sometimes there are changes in the immune system.

We can distinguish 4 groups of disorders affecting the immune system:

  • Immunodeficiency
  • Autoimmunity
  • Allergic disorders
  • Cancer immunity


old people sitting on a bank

Immnune system becomes weaker as we get older

Having a strong immune system is the best guarantee not to succumb to disease. The body is seriously affected when the immune system is severely impaired and unable to respond to attack by external agents.

In these cases, it is said that the body has immune deficiency. This type of situation can be caused by the continued existence of certain diseases that will progressively weaken it such as those originated by certain bacteria or viruses.

Immunodeficiency can be primary or acquired. In the first case, it includes a number of diseases with a genetic trait that affect the immune system from the early years.

The acquired immune deficiencies are caused by a number of non-genetic causes that weaken the immune system. Among them, we can mention the following: diseases that attack the immune system, especially those affecting the bone marrow or defense cells such as leukemia or lymphoma.

Other factors that affect immunity are inadequate nutrition, aging, transplants or certain medicines.

Currently the most important disease causing adquired immunodeficiency is AIDS. This disease destroys the immune system so the body is defenseless against the invasion of many external agents or the increase of many diseases (pneumonia, tuberculosis, chickenpox, herpes, mouth fungus, syphilis, mental problems, joint pain, etc)

punto rojo More information on immune system.

Written by Editorial Botanical-online team in charge of content writing

19 March, 2019

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