How Does the Immune System Fight Illnesses and Keep Us Healthy?

The immune system plays a vital role in keeping us healthy by fighting illnesses and infections. It’s often the reason we feel unwell when we have an infection, but it’s also the reason we are able to recover from that same infection.

The system is a collection of cells, channels and nodes that work together as an orchestra when working effectively. Approximately 70% of our immune system is located in our gut (Vighi et al., 2008) and the health of our micro biome and gut bacteria is considered to be the main link between the immune system, health and our susceptibility to disease.

We think of the immune system as a fully integrated system; however, it has two subsystems: the innate and adaptive immune systems. Both are essential in preventing disease and function in very different ways.

The innate system

The innate immune system is the body’s first line of defence against an infection. The innate system provides  a physical protection barrier to the world to help prevent infection and pathogens entering our body.

Within the system are specialised cells that attack pathogens as they enter our body. Cells including neutrophils, macrophages and dendritic cells, absorb pathogens into their cells where they destroy them.

The innate immune system is ready to go into immediate action as it targets and destroys infection. It has specialised cells that attack any pathogen that enters our body. These cells are present throughout the body and can act within minutes to kill invading microbes and limit the damage that they can cause to the body.

This system responds in the same way to all virus and doesn’t have the ability to memorise the pathogen but has to create new receptors to adapt to each immune response. Also, it can’t always defeat all pathogens. That’s where the second, more specialised, line of defence comes into play.

The adaptive system

The adaptive immune system is slower to kick into action but uses different techniques to destroy different microbes. It works together with the innate system to kill foreign invaders.

There are three major cell types associate with the adaptive immune system: B cells, helper T cells and killer T cells.

B cells are lymphocytes which arise in the bone marrow and differentiate into plasma cells which in turn produce antibodies (immunoglobulins). Antibodies are small chemicals that are able to bind to some microbes and prevent them entering cells or bind to the toxins that some pathogens produce and neutralise their effect. Antibodies also “flag” microbes so innate cells can more easily destroy them.

Helper T-cells, as the name implies, are specialised lymphocytes which ‘help’ other T-cells and B-cells to perform their functions. They allow innate cells to see and kill pathogens and help B cells make the right type of antibody to most appropriately deal with a pathogen.

Natural killer T (NKT) cells secrete chemicals to directly kill cells infected by a virus. A virus cannot exist outside a cell and they have to invade the cells of a host to multiply. Once a killer T cell identifies an infected cell it kills off the whole cell to prevent the preventing the virus from multiplying. The dead cell is then swept away by the innate system.

Once the adaptive immune system has encountered a pathogen it will remember it for any future exposure and react with a quicker and stronger response. You may not even know that you have come into contact with future contamination. This is why you generally only get diseases like the mumps once. This idea has been used to develop the concept of vaccinations.

Vaccinations deliver a carefully measured dose of a pathogen to your immune system. The amount is so small that it doesn’t make us sick but primes our immune system to recognise the pathogen so that if we get exposed to it in the future our adaptive immune system will respond quickly.

Vaccines are just one way to improve your immune system. There is increasing evidence that a diet high in fibre will also influence your immune system and and so will some supplements.

What happens when the immune system goes wrong?

Sometimes the immune system attacks the body’s own tissues. Allergies, such as hay fever, allergic asthma or atopic dermatitis), are caused by an immune response to an invader that won’t cause disease.

Instead of guarding against pathogens the immune system sometimes will sense healthy tissues as foreign invaders and sends out cells to attack them.

For instance, Type 1 diabetes damages the pancreas, while systematic lupus erythematosus (SLE) will attack the entire body. The body’s protector has now become it’s enemy.

Scientists are constantly working on understanding more about the immune. One field of work is to develop new vaccines to improve our response to destroying cancers cells. Another area is the study of treatment to reduce the body’s reaction to auto immune diseases without hindering our ability to respond to dangerous pathogens. Nutritionists are looking at how the food that we eat and our general lifestyle plays a part in our gut health which in turn has a role in the overall health of our immune system.

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