Introduction

When you become ill, the immune system is responsible for preventing disease and infection. It eliminates pathogens – microorganisms that can enter the body and cause harm. These can include bacteria, viruses, and parasites. Many organs work together to fight against these germs. You may already be familiar with the concept of white blood cells (leukocytes), which are heavily involved in immunity.¹

A healthy immune system is active when needed and knows what it should destroy or ignore. Recurrent infections can result from a weak immune system, while an overactive immune system causes the body’s cells to attack themselves. This article will explain the different aspects of the immune system and how to keep it functioning at its best.

Components of the immune system 

Innate immunity

Our body has multiple lines of defence against pathogens. The first barrier that pathogens encounter is the innate immune system.^2,3 This helps initiate the primary immune response with the help of some key components: 

• The skin: Our skin is the largest organ we have, made up of dead skin cells. It acts as a waterproof barrier
• Mucosal membranes line inner cavities such as the lungs, nose, and stomach. They are covered in mucus, a sticky substance that traps dirt and prevents it from moving further into the body 
• Phagocytes, from ‘phage’, meaning eater, and ‘cyto’, meaning cell. These cells engulf pathogens, destroying them in the process 
• Complement: Proteins in our blood that help destroy germs, causing their contents to spill out
• Natural killer cells: A type of white blood cell that kills infected cells 

Adaptive immunity

Adaptive immunity can be thought of as the second line of defence. The adaptive and innate immune systems are linked by antigen-presenting cells, which use pathogen cell markers to flag infected cells for destruction. Adaptive immunity involves antibodies, specialised molecules that recognise and neutralise pathogens. These players feature in the secondary immune response after reinfection:⁴

• B cells: Produce antibodies against previously encountered pathogens
• T Helper cells: Send signals that recruit other cells for assistance 
• T Killer cells (or cytotoxic T cells): Destroy infected cells 
• T Regulatory cells: Prevent T Killer cells from attacking healthy cells 
• Antibodies: Also known as immunoglobulins, they come in different types. They attach to antigens and tag them for attack by other immune cells

Organs of the immune system

The immune system includes organs in addition to cells. There are primary and secondary immune organs that play a part in lymphocyte development. The adaptive immune system relies on lymphocytes to create a specific response.^4,5 Organs involved in this process are part of the lymphatic system: 

Primary lymphoid organs

• Bone marrow: Where blood cells are produced
• Thymus: Where T cells learn to recognise non-self antigens

Secondary lymphoid organs

• The spleen: Where lymphocytes can be found after development; this organ also filters the blood
• Tonsils: Contain white blood cells and prevent germs from entering the mouth or nasal cavity
• Lymph nodes: Found throughout the body, they filter lymph fluid, a clear substance containing lymphocytes

Factors influencing immune system health 

To avoid infection, we can aim to take care of our immune system. Immune system health is affected by a variety of factors that are tied together.⁶ It should be emphasised that the immune system is not controlled by one overarching factor, making it important to consider all of these when improving one’s immune health:

• Genetic predisposition to disorders of the immune system, such as DiGeorge syndrome 
• Age: DNA damage that accumulates over time, along with the decline of the thymus, leads to reduced immune health in the elderly
• Lifestyle: smoking and alcohol misuse can negatively affect the immune response^7,8
• Medication: immunosuppressant drugs may increase the likelihood of infection in patients who take them 
• Nutrition
• Gut health⁹
• Stress

Assessing immune system health 

Many tools are available to check our immune health, and some of these tests may be used in a diagnosis:

• Full blood count (FBC)

• Immunoglobulin levels 
• Genetic testing
• Allergy testing

Disorders of the immune system can cause symptoms that range from mild to severe. These symptoms can also overlap with those of other diseases, making it difficult for a doctor to pinpoint the root cause of the problem. Keeping a record of your experiences will help with the investigation. Allergies are a common type of immune disorder, caused by your body labelling something harmless as foreign. The body then sets out to attack, leading to inflammatory symptoms such as:

• Frequent sneezing
• Coughing
• Pink eye (conjunctivitis)
• Runny nose
• Itchy eyes, throat, mouth, nose, or ears
• Anaphylactic shock: A life-threatening reaction caused by allergic triggers
• Pain in joints, muscles, or bones that aren’t caused by injury, or pain in multiple areas of the body, may indicate rheumatoid arthritis, an autoimmune disease

Strategies to boost immune system health

There is no single way to boost immune health; a combination of good habits can enhance its ability. It should be noted that supplementation alone will not lead to a healthy immune system and it should be accompanied by adequate sleep and regular exercise for the best effect. Listed below are ways in which you can support your immune system:

• Eating a balanced diet: Staying away from a Western diet full of processed foods can improve the gut microbiome, leading to positive immune effects ⁹
• Exercise: Regular physical activity is a key part of a healthy lifestyle, and the immune system responds positively to exercise ¹⁰
• Getting enough sleep ¹¹
• Stress management: Alleviating chronic inflammation through stress management can be beneficial. Meditation, breathing exercises, and finding support can help 
• Avoiding harmful habits: Such as smoking and limiting alcohol consumption 

Common misconceptions about the immune system

Myth: Cold weather weakens the immune system

More people seem to fall ill during the winter months. However, the weather does not affect immune function. In fact, in response to the cold, your body’s immune system activates to adapt.¹² This response is small, so other factors may be to blame. Germs thrive in the crowded environments that humans create indoors, as well as in the low-humidity conditions of winter.¹³ Therefore, these factors may be responsible instead of our immune systems. 

Myth: Boosting the immune system through supplements 

Without dietary or lifestyle changes, your immune health is unlikely to improve significantly. The effect of vitamin and mineral supplements varies from person to person, depending on how each individual breaks them down and absorbs them.¹⁴ Furthermore, our dietary habits also affect how well we absorb supplements. Incorporating other good habits can be more beneficial for our immune system.

Summary 

Without the immune system, our bodies would be unable to fight off disease. It is made up of many different cells and organs, which play intertwined roles in protecting us from germs. We can support our immune system by engaging in healthy lifestyle choices, such as regular exercise, proper sleep, and eating a balanced diet.

To monitor our immune health, it is recommended to have regular check-ups so that any problems can be identified early. If you experience symptoms of inflammation or reactions to food or other environmental triggers, it may be helpful to undergo testing for allergies. Your doctor may recommend certain anti-allergy medications to keep symptoms at bay.