How The Immune System Works

The immune system is a critical part of the human body, providing protection against unwanted invaders such as infectious organisms. Known as the immune response, the immune system launches a series of steps against any organisms it identifies as unwanted.

Having a compromised immune system can leave an individual extremely vulnerable and exposed to the risk of becoming very ill as a result of commonplace infections and organisms.

Everyone has heard of the immune system but not many people really understand how it actually works. Here’s a closer look at the structure and functions of the immune system.

The Basics of the Immune System

The immune system is an extremely complicated network within the body and made up of a variety of cells, proteins, tissues and organs which combine to provide protection for the body against unwanted substances.

The function that the immune system performs is extremely complex, identifying the body’s own tissue from bacteria, viruses, parasites and other unwanted foreign bodies. Some of the key components within the immune system include:

  • Lymph nodes – store and produce infection-fighting cells
  • Bone marrow – produces white cells, also known as leucocytes
  • Thymus – T-cells mature in this organ; they are essential for getting rid of cancerous or infected cells
  • Spleen – the largest organ within the lymphatic system, the spleen holds the vital white blood cells
  • White blood cells – leucocytes are a small white blood cell which plays a major part in actively eliminating disease.

White Blood Cells

Although there are many parts to the immune system, the white blood cells play a particularly vital role in defending the body. Although often referred to collectively as white blood cells, there are different types of white blood cell within the immune system.

Leucocytes are produced and stored in numerous locations all over the body, sheltered by the lymphoid system. Leucocytes patrol the body, moving around all the organs via the circulatory system, moving between blood vessels and lymphatic vessels. As they move around the body, these leucocytes are constantly on the alert for any sign of unwanted invasion.

There are two main types of leucocyte: phagocytes and lymphocytes.


Neutrophils are the most common type of leucocyte and are designed to fight bacteria. A raised neutrophil count is one of the things that doctors test for if they suspect a bacterial infection. There are also specific types of phagocyte which are matched to directly identify and fight certain types of invaders.

Some other types of phagocytes include eosinophils, basophils, mast cells, dendritic cells and macrophages.


Lymphocytes are grouped into B-cells and T-cells, both of which start life in the bone marrow. B-cells remain there to mature while T-cells move to the thymus to complete their development. B-cells are intelligence gatherers, responsible for seeking out invaders and then locking onto their position. The T-cells can be conserved to be soldiers, whose mission it is to follow the signals laid down by the B-cells and destroy the invaders.

The Body’s Immunity

The human body has three different types of immunity which is provided by the immune system and are as follows:


This type of immunity is something that people are born with which means that certain viruses or infection won’t do any harm. For example, certain diseases that affect other species will not make a human ill, such as feline HIV.

Another example of innate immunity is the barriers that are in place to protect the body, such as the mucous membranes and the skin. If this barrier is breached, the body works hard to repair it quickly and special cells from the immune system attack any invaders who attempt to gain access.


This is a particularly complex type of immunity which evolves during the lifetime. As individuals are either exposed to diseases or immunised, the body begins to recognise viruses much more quickly in the future. This allows a far more rapid immune response and creates a more effective immune system.


Not all immunity is permanent; passive immunity is just a temporary state. This type of immunity is borrowed from another source, such as a baby who benefits from its mother’s breast-milk.

A Clever System

The immune system is an incredibly complex mechanism, which can be seen from the descriptions above, which draws upon a number of different components to offer  a complete solution. As well as more general protective cells, there are many types of special immune cell which have a very specific job, or have been created to respond to a specific type of invader.

Immune disorders can occur, either as a primary condition or as a secondary complication to conditions such as malnutrition or burns. Problems with the immune system can have a very profound effect on the body’s ability to function and care for itself, and can prove fatal.