Immune system.

Your immune system defends the body from infection. It is made up of a complex network of cells, tissues and organs in your body. An underactive or overactive immune system can cause health issues.

What is the immune system?

The immune system is found in:


_bone marrow.

_the thymus, a gland in your upper chest.

_white blood cells, which fight infection.

_lymph, a milky fluid carrying white blood cells.

_the lymphatic system, a network of tiny vessels that carry lymph around the body. _lymph nodes, small lumps in your groin, armpit, around your neck and elsewhere.

_the spleen, an organ under your ribs on the leftmucous membranes, like the lining of the inside of your mouth.

The lymphatic system allows immune cells to travel between tissues and the bloodstream. The lymphatic system contains lymphocytes (white blood cells; mostly T cells and B cells), which try to recognise any bacteria, viruses or other foreign substances in your body and fight them.

Lymph nodes are found in certain areas such as the base of the neck and the armpit. They become swollen or enlarged in response to an infection.

How does the immune system work?

The skin and mucous membranes are the first line of defence against bacteria, viruses and other foreign substances. They act as a physical barrier, and they also contain immune cells.

When your skin has a cut, harmful microbes (tiny particles) can enter and invade your body. The cut triggers certain immune cells in the bloodstream that try to destroy the invaders.

In an infection, white blood cells identify the microbe, produce antibodies to fight the infection, and help other immune responses to occur. They also ‘remember’ the attack.

This is how vaccinations work — vaccines expose your immune system to a dead or weakened microbe or to proteins from a microbe, so that your body is able to recognise and respond very quickly to any future exposure to the same microbe.

Related conditions.

Overactivity of the immune system is related to disorders such as allergies and autoimmune diseases.

Allergies involve an immune response to something considered harmless in most people, such as pollen or a certain food.

Autoimmune diseases, such as multiple sclerosis and rheumatoid arthritis, occur when your immune system attacks normal components of the body.

Underactivity of the immune system, or immunodeficiency, can increase your risk of infection. You may be born with an immunodeficiency, or acquire it due to medical treatment or another disease.

_Types of immunity:


Innate, or nonspecific, immunity is the defense system with which you were born. It protects you against all antigens. Innate immunity involves barriers that keep harmful materials from entering your body.

These barriers form the first line of defense in the immune response. Examples of innate immunity include:

_Cough reflex.

_Enzymes in tears and skin oils.

_Mucus, which traps bacteria and small particles.


_Stomach acid.

Innate immunity also comes in a protein chemical form, called innate humoral immunity. Examples include the body’s complement system and substances called interferon and interleukin- (which causes fever).

If an antigen gets past these barriers, it is attacked and destroyed by other parts of the immune system.


Acquired immunity is immunity that develops with exposure to various antigens. Your immune system builds a defense against that specific antigen.


Passive immunity is due to antibodies that are produced in a body other than your own. Infants have passive immunity because they are born with antibodies that are transferred through the placenta from their mother. These antibodies disappear between ages 6 and 12 months.

Passive immunization may also be due to injection of antiserum, which contains antibodies that are formed by another person or animal. It provides immediate protection against an antigen, but does not provide long-lasting protection. Immune serum globulin (given for hepatitis exposure) and tetanus antitoxin are examples of passive immunization.

The immune system is made up of special organs, cells and chemicals that fight infection (microbes).

The main parts of the immune system are:

white blood cells, antibodies, the complement system, the lymphatic system, the spleen, the thymus, and the bone marrow. These are the parts of your immune system that actively fight infection.


The immune system includes certain types of white blood cells. It also includes chemicals and proteins in the blood, such as antibodies, complement proteins, and interferon. Some of these directly attack foreign substances in the body, and others work together to help the immune system cells.

Lymphocytes are a type of white blood cell.

The lymphatic system is a network of delicate tubes throughout the body.

The main roles of the lymphatic system are to:

1. manage the fluid levels in the body.

2. react to bacteria.

3. deal with cancer cells .

4. deal with cell products that otherwise would result in disease or disorders.

5. absorb some of the fats in our diet from the intestine.

The lymphatic system is made up of:

_lymph nodes (also called lymph glands) — which trap microbes.

_lymph vessels — tubes that carry lymph, the colourless fluid that bathes your body’s tissues and contains infection-fighting white blood cells.

_white blood cells (lymphocytes).

There are B and T type lymphocytes.

B lymphocytes become cells that produce antibodies. Antibodies attach to a specific antigen and make it easier for the immune cells to destroy the antigen.

T lymphocytes attack antigens directly and help control the immune response. They also release chemicals, known as cytokines, which control the entire immune response.

As lymphocytes develop, they normally learn to tell the difference between your own body tissues and substances that are not normally found in your body. Once B cells and T cells are formed, a few of those cells will multiply and provide “memory” for your immune system. This allows your immune system to respond faster and more efficiently the next time you are exposed to the same antigen. In many cases, it will prevent you from getting sick. For example, a person who has had chickenpox or has been immunized against chickenpox is immune from getting chickenpox again.

The immune system and microbial infectionThe immune system keeps a record of every microbe it has ever defeated, in types of white blood cells (B- and T-lymphocytes) known as memory cells. This means it can recognise and destroy the microbe quickly if it enters the body again, before it can multiply and make you feel sick.

Some infections, like the flu and the common cold, have to be fought many times because so many different viruses or strains of the same type of virus can cause these illnesses. Catching a cold or flu from one virus does not give you immunity against the others.


Antibodies help the body to fight microbes or the toxins (poisons) they produce. They do this by recognising substances called antigens on the surface of the microbe, or in the chemicals they produce, which mark the microbe or toxin as being foreign. The antibodies then mark these antigens for destruction. There are many cells, proteins and chemicals involved in this attack.

The body’s other defences against microbesAs well as the immune system, the body has several other ways to defend itself against microbes, including:

_skin :

a waterproof barrier that secretes oil with bacteria-killing properties.

_lungs :

mucous in the lungs (phlegm) traps foreign particles, and small hairs (cilia) wave the mucous upwards so it can be coughed out.

_digestive tract :

the mucous lining contains antibodies, and the acid in the stomach can kill most microbes.

_other defences :

body fluids like skin oil, saliva and tears contain anti-bacterial enzymes that help reduce the risk of infection. The constant flushing of the urinary tract and the bowel also helps.

_Fever is an immune system response.

A rise in body temperature, or fever, can happen with some infections. This is actually an immune system response. A rise in temperature can kill some microbes. Fever also triggers the body’s repair process.

_Common disorders of the immune system.

It is common for people to have an over- or underactive immune system.Overactivity of the immune system can take many forms, including:

Healthy ways to strengthen your immune systemYour first line of defense is to choose a healthy lifestyle.

Following general good-health guidelines is the single best step you can take toward naturally keeping your immune system working properly. Every part of your body, including your immune system, functions better when protected from environmental assaults and bolstered by.

healthy-living strategies such as these:

_ Don’t smoke.

_ Eat a diet high in fruits and vegetables.

_ Exercise regularly.

_ Maintain a healthy weight.

_ If you drink alcohol, drink only in moderation Get adequate sleep.

_ Take steps to avoid infection, such as washing your hands frequently and cooking meats thoroughly.

_ Try to minimize stress.

_ Keep current with all recommended vaccines.

Vaccines prime your immune system to fight off infections before they take hold in your body.

References :

Immune system”,

“Immune response”,

“Immune system explained”,

“How to boost your immune system”,

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