The immune system is a complex network of cells and proteins that work together to provide the body’s defence system...

...protecting your body from harmful microbes (pathogens) that can cause disease and illness. To function properly, the immune system must detect a wide variety of pathogens and distinguish them from the body's own healthy cells.

Antigens, proteins found on the surface of the pathogen, are "targeted" by antibodies. Each antibody is specifically produced by the immune system to match an antigen after cells in the immune system come into contact with it; this allows a precise identification or matching of the antigen and the initiation of a tailored immune response.

Where in the body is the immune system?

The immune system comprises numerous cell types which do not form a single organ like the heart or liver. Instead, the immune system is dispersed throughout the body to provide rapid immune responses. Cells travel through the bloodstream or in specialized vessels called lymphatics. Lymph nodes and the spleen provide structures that facilitate cell-to-cell communication. Each cell type plays a unique role, with different ways of recognizing problems, communicating with other cells, and performing their functions.

The main parts of the immune system are:                                                   

  • white blood cells
  • antibodies
  • lymphatic system
  • spleen
  • bone marrow
  • thymus

White blood cells

White blood cells, also called leukocytes. are the key players in your immune system. They are made in your bone marrow and are part of the lymphatic system. White blood cells are on constant patrol. They circulate through blood and tissue throughout your body, looking for foreign invaders (microbes) such as bacteria, viruses, parasites and fungi. When they find them, they launch an immune attack. They multiply and send signals out to other cell types to do the same.

There are two main types of leukocyte:

1. Phagocytes

These cells surround and absorb pathogens and break them down, effectively eating them.

2. Lymphocytes

Lymphocytes help the body to remember the invaders and recognize them if they come back to attack again.

Lymphocytes begin their life in bone marrow. Some stay in the marrow and develop into B lymphocytes (B cells), others head to the thymus and become T lymphocytes (T cells). These two cell types have different roles:

B lymphocytes — they produce antibodies and help alert the T lymphocytes.

T lymphocytes — they destroy compromised cells in the body and help alert other leukocytes.


Antibodies help the body to fight microbes or the toxins they produce.

B lymphocytes are triggered to make antibodies. Each B cell makes one specific antibody. For instance, one might make an antibody against the bacteria that cause pneumonia, and another might recognize the common cold virus. The antibodies stay in a person's body. That way, if the immune system encounters that antigen again, the antibodies are ready to do their job. That is why with some diseases, such as chickenpox, you only get it once as the body has a chickenpox antibody stored, ready and waiting to destroy it next time it arrives. This is called immunity.

Although antibodies can recognize an antigen and lock onto it, they can't destroy it without help. That's the job of the T cells. They destroy antigens tagged by antibodies or cells that are infected or somehow changed. (Some T cells are actually called "killer cells.") T cells also help signal other cells (like phagocytes) to do their jobs.

Lymphatic system

The lymphatic system is a network of delicate tubes throughout the body. The main roles of the lymphatic system are to:

  • manage the fluid levels in the body
  • react to bacteria
  • deal with cancer cells
  • deal with cell products that otherwise would result in disease or disorders
  • 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)


The spleen is a blood-filtering organ that removes microbes and destroys old or damaged red blood cells. It also makes disease-fighting components of the immune system (including antibodies and lymphocytes).

Bone marrow

Bone marrow is the spongy tissue found inside your bones. It produces the red blood cells our bodies need to carry oxygen, the white blood cells we use to fight infection, and the platelets we need to help our blood clot.


The thymus, a small organ located in the upper chest, filters and monitors your blood content. It produces the white blood cells called T-lymphocytes. T cells mature in the thymus.

Fever is an immune system response

A fever (also termed pyrexia) is a higher-than-normal body temperature. It is a symptom with a wide variety of causes, viruses and bacteria being among the most frequent in adults. A fever is an immune system response to encourage chemical reactions that will increase production of disease-fighting antibodies, stimulate activity of white blood cells and even inhibit the invading microbe's growth. It is a good indication that the immune system is doing it’s job.

Weak Immune System

If the immune system becomes weakened (it is not perfect) the body becomes more susceptible to infections and illnesses which might be more severe or harder to treat.

Infections that people with a weak immune system may get more frequently include:

  • pneumonia
  • meningitis
  • bronchitis
  • skin infections
  • Other symptoms of a weak immune system can include:
  • autoimmune disorders
  • inflammation of the internal organs
  • blood disorders or abnormalities, such as anaemia
  • digestive issues, including loss of appetite, diarrhoea, and abdominal cramping
  • growth and developmental delays in infants and children


Stress can weaken the immune system further and make a person more susceptible to illness.

Research shows that a person who is under excessive stress is more likely to get sick.

Practices that may reduce and manage stress include:

  • yoga
  • meditation
  • massages
  • spending time pursuing hobbies

To maintain a healthy immune system:

  • Vitamins and supplements
  • Try to minimize stress
  • 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
  • Don’t smoke

Here is a link to a very informative podcast about Brain Inflammation    


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