The immune system is the body’s main defence against infection and disease, and apart from our nervous system, it is the most complex network of cells, organs, tissues and proteins that we have. We become ill when our immune system is compromised, or if a germ or virus either goes undetected or is aggressive enough to overcome our defences.

The body’s security

The cells and molecules that make up our immune system are distributed throughout our body, but work together to prevent infection and suppress disease. Imagine them as your body’s security force, constantly vigilant against dangerous intruders. As well as guarding against alien pathogens, the immune system watches out for other harmful substances in the environment and does its best to neutralise them. The body’s own cells are also monitored as these may also need to be eliminated if they have been transformed by an illness such as cancer.

The immune response works by distinguishing between cells that belong in the body and those that could do it harm. These are defined as “self” and “non-self.” The immune system is actually made up of two different “departments” that complement each other in defending your body: innate immunity and adaptive immunity.

Innate defence

Innate immunity provides a general defence against harmful cells or pathogens, including bacteria, viruses, parasites and fungi. The first line of defence is the skin and mucous membranes that attempt to stop these substances from entering. Various acids, enzymes and mucous also try to stop pathogens from settling, and tears, sweat and urination are all means of effectively flushing them out.

If the pathogens get into the body, then specialist natural killer (NK) cells and plasma proteins are ready to go into action against them. Inflammatory cells will swiftly move to the area infected, and as blood circulation is increased and soluble proteins are activated, this can lead to inflammation and the affected area becoming swollen and hot. You may also suffer from a fever. These are all signs that your body is battling infection.

Adaptive immunity

If the innate immune system isn’t successful after roughly four to seven days, then the adaptive immune system will kick in. This takes longer to react to illness as it is more specialised, and relies on recognising antigens and formulating a specific defence against them. To this end, the adaptive immune system forms memory cells and remembers antigens that it has met before, and how to combat them. This is why you can become immune to an illness after having it once, and is also how vaccination works, by introducing an antigen to the immune system so that it will recognise it and fight against it effectively in future.


Immunologists are doctors who specialise in the immune system and issues arising from it. They may be purely research scientists or medical practitioners who combine research with caring for patients who have immune system disorders and who are referred to them by GPs or hospitals. Significant figures in immunology include Louis Pasteur and Edward Jenner, the developer of the smallpox vaccine.

Dr. Robert Ryan, from Dundee, worked as programme manager for Wellcome Trust’s four-year PHD at the University of Dundee, where he performed a wide range of immunology experiments and developed techniques in advancing anti-bacterial research. In his work as a microbiologist and medical writer, Dr. Ryan has been the recipient of numerous grants, fellowships and awards. The best way to pursue a career in immunology is to take a medical career and then specialise, taking a PHD at a university with an established immunology department.

Immunodeficiency and autoimmune disorders

Serious problems can occur if the immune system doesn’t function correctly. Primary immunodeficiency disorders exist from birth and are quite rare; more common are secondary immunodeficiency disorders that develop later in life. In both cases, serious infections can take hold and not go away, leading to further complications that can sometimes be fatal.

The immune system can also sometimes begin to attack native cells due to a defect that renders it unable to distinguish between self and non-self. This is called an autoimmune reaction. Examples of autoimmune diseases include Crohn’s disease, rheumatoid arthritis and type 1 diabetes. In the case of cancer, cell growth within the body becomes abnormal and uncontrolled, and these cells evade destruction by the immune system. Scientists are looking for ways to manipulate the immune system into fighting cancerous tissue. At the opposite end of the spectrum, successful organ transplants rely on the immune system accepting the new organ as “self” and not rejecting it.

Research into our immune systems is important work, and vital discoveries are still being made. We have much to thank our body’s security force for, and the better we understand it, the more we can help it work effectively.

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