How does the immune system work? Learn all about your immunity
What is the immune system?
The immune system is located throughout our entire body, including on the skin, in the intestines, respiratory system, blood, and lymphatic system. It is a highly complex system with the aim of detecting and neutralising all harmful substances and cells in the body. These can be pathogens such as bacteria, parasites, fungi, and viruses, but also damaged or mutated cells or toxins from processed foods, air pollution, cigarette smoke, heavy metals, radiation (such as excessive sunlight), or chemicals in personal care products and cosmetics.
How does the immune system work?
Our immune system is composed of many different components. Each component plays a unique role in recognising foreign substances, communicating with other parts of the immune system, and fighting an infection. The foundation of our immune function is our blood and lymph fluid. Together, these two fluids transport all elements of the immune system so it can function properly. Our immune system consists of:
- The skin and mucous membranes – The skin and mucous membranes form the first line of defence and are the barrier against external influences. Mucous membranes are found in our eyes, mouth, nose, respiratory system, intestines, and around the genitals. All mucous membranes produce mucus and have tiny hairs to expel intruders. Moreover, billions of beneficial bacteria reside on the skin and mucous membranes. These permanent residents are called flora (skin flora, gut flora, etc.) and are part of our microbiome. Our microbiome, like stomach acid and saliva, also contributes to the first line of defence against pathogens.
- White blood cells – our white blood cells are also known as the soldiers of the immune system. The different types of white blood cells (phagocytes and lymphocytes) are responsible for the immune response to unwanted invaders and their elimination.
- Natural killer cells (NK cells) – are a type of lymphocyte (white blood cell) responsible for neutralising harmful and infected cells. Natural killer cells earn their name from their ability to specifically destroy harmful cells at an early stage, preventing spread and further infection.
- The lymphatic system - a network of lymph nodes and small vessels through which immune cells can travel between tissues and the bloodstream. The milky fluid that flows through our lymphatic system is called lymph or lymph fluid.
- The lymph nodes - small, bean-shaped glands found throughout the body but particularly concentrated in the neck, armpits, groin, and abdomen. The lymph nodes are connected via lymphatic vessels. Immune cells gather in lymph nodes where they can quickly respond when antigens are detected. Such an immune response can lead to swelling of the lymph nodes.
- The thymus - a gland behind our breastbone where lymphocytes (white blood cells) mature. The thymus is also part of the lymphatic system.
- The tonsils – the tonsils are part of the lymphatic system and are considered the gatekeepers of our immune system in the upper respiratory tract.
- The bone marrow – responsible for the production of red and white blood cells.
- The spleen - a fist-sized organ located under the left ribs. The spleen is part of our lymphatic system and plays, along with the liver and kidneys, a crucial role in filtering and cleansing our blood. Additionally, the spleen also forms the two types of white blood cells (phagocytes and lymphocytes).
- Peyer's patches – a specific type of tissue in the small intestine that essentially forms an isolated part of the immune system. Peyer's patches contain a cluster of lymph nodes filled with white blood cells. This allows them to identify and eliminate pathogens (such as bacteria) from digested food without triggering a full immune response from the body.
- The gut flora – our gut flora or gut microbiome is the entire population of bacteria, yeasts, and fungi that inhabit our intestines. The population density in our gut, especially in our large intestine, is so high that under normal, healthy conditions, there is no room for pathogens to settle. Should a pathogen linger, the immune system in the gut will act as a safety net, and the aforementioned active immune cells will promptly respond.
- The appendix – a lesser-known part of our immune system is the appendix, also known as the vermiform appendix. This tissue is also part of our immune system because the appendix promotes the growth of healthy gut bacteria. Scientists also suspect that this organ serves as a storage place for good gut bacteria.
The immune system can further be divided into two major components: the innate immune system and the adaptive immune system.
The innate immune system
The innate immune system is the part of our immunity that is passed on from our mother at birth. The cells in our innate immune system are the first responders and are not specifically set for a particular type of pathogen. They react quickly and efficiently to a wide range of invaders.
The innate immune system is also the second line of defence and is activated as soon as a pathogen breaches our skin or mucous membranes. The innate immune system consists not only of phagocytes and natural killer cells but also signal substances. The function of the signal substances is to activate and also timely inhibit certain parts of the immune system.
The acquired or adaptive immune system
The adaptive – also known as acquired or learned – immune system develops as you are exposed to various pathogens. It is our third line of defence and the part that activates when the innate immune system cannot completely eliminate the invader. This system reacts more slowly but has the ability to adapt to specific invaders, remember them, and recognise them in case of a future infection. The adaptive immune system consists of different types of cells, including T-lymphocytes (T-cells) and B-lymphocytes (B-cells).
When a pathogen is detected in our body, both T and B cells are activated. T-lymphocytes help directly combat the invaders by attacking and destroying them. B-lymphocytes produce antibodies, also known as immunoglobulins, which attach to the pathogens and neutralise them. These antibodies can also serve as a signal for other immune cells to attack the invaders.
Another important aspect of the adaptive immune system is the so-called immunological memory. This means that the adaptive immune system develops a recognition mechanism after an initial infection to combat the invader faster and more efficiently during a subsequent infection.
The different types of white blood cells
The white blood cells are the commanders of our health army. As we explain above, it is the white blood cells that first respond when an invader appears. There are different types of white blood cells that we can categorise into phagocytes and lymphocytes.
Phagocytes
Phagocytes include macrophages, neutrophils, monocytes, dendritic cells, and mast cells. They are the type of white blood cell that constantly searches for viruses, dead cells, and other pathogens through our blood vessels and tissues. They are an important part of our innate immune system, where a non-specific immune response is elicited against pathogens. When a phagocyte discovers a foreign organism, it immediately disposes of it through a process called phagocytosis (enclosure). Once enclosed, the pathogen is digested and neutralised.
Lymphocytes
Lymphocytes are small white blood cells that defend the body against pathogens, foreign substances, and tumour cells. Lymphocytes include T-cells, B-cells, and natural killer cells. Lymphocytes mainly circulate in the blood and lymphatic system but are also found in the bone marrow, spleen, thymus, liver, lymph nodes, and tonsils. Unlike phagocytes, lymphocytes generate a specific immune response against pathogens. This specific immune response is called the adaptive immune system.
How can I boost my immunity?
The health of our immunity not only determines how well we can withstand seasonal illnesses but also how quickly we recover. To boost your immune system or keep it in good condition, it is important to take good care of yourself. Adequate rest, good sleep, daily outdoor activity, a healthy diet rich in vitamins C, D, zinc and antioxidants, regular exercise, and reducing stress are all factors essential for a well-functioning immune system. Supporting your gut can also make a big difference. In this blog, you can read more about how healthy intestines contribute to strong immunity.
