How does the immune system work? Learn all about your immunity
What is the immune system?
The immune system is present throughout our body, including the skin, intestines, respiratory tract, 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 include pathogens like bacteria, parasites, fungi, and viruses, as well as 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 part plays a unique role in recognising foreign substances, communicating with other parts of the immune system, and combating an infection. At the core of our immune function are our blood and lymphatic fluid. Together, these two fluids transport all the elements of the immune system, ensuring it functions properly. Our immune system includes:
- The skin and mucous membranes – The skin and mucous membranes form the first line of defence and act as a barrier against external influences. Mucous membranes are found in our eyes, mouth, nose, respiratory tract, intestines, and around the genitals. All mucous membranes produce mucus and have cilia to expel intruders. Moreover, billions of beneficial bacteria reside on the skin and mucous membranes. These permanent residents are known as flora (skin flora, gut flora, etc.) and are part of our microbiome. Our microbiome, along with stomach acid and saliva, also contributes to the initial line of defence against pathogens.
- White blood cells – our white blood cells are also known as the soldiers of the immune system. The various 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 are so named because they specifically destroy harmful cells in the early stages, 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 known as lymph or lymphatic fluid.
- The lymph nodes - small, bean-shaped glands found throughout the body, primarily concentrated in the neck, armpits, groin, and abdomen. The lymph nodes are interconnected via lymphatic vessels. Immune cells gather in lymph nodes, allowing them to react quickly when antigens are detected. Such an immune reaction can cause swelling of the lymph nodes.
- The thymus - a gland located 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, among other functions.
- The spleen - a fist-sized organ located under the left ribs. The spleen is part of our lymphatic system and plays a crucial role, along with the liver and kidneys, in filtering and cleansing our blood. Additionally, the spleen forms the two types of white blood cells (phagocytes and lymphocytes).
- Peyer's patches – a specific type of tissue in the small intestine that functions as an isolated part of the immune system. Peyer's patches contain clusters of lymph nodes filled with white blood cells, enabling 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 inhabiting our intestines. The population density in our gut, particularly in the large intestine, is so high that under normal, healthy conditions, there is no space for pathogens to settle. Should a pathogen linger, the immune system in the gut acts as a safety net, and the aforementioned active immune cells will immediately respond.
- The appendix – a lesser-known component of our immune system is the appendix, also known as the vermiform appendix. This tissue is part of our immune system as it promotes the growth of healthy gut bacteria. Scientists also suspect that this organ serves as a storage site for beneficial gut bacteria.
The immune system can further be divided into two main components: the innate immune system and the adaptive immune system.
The innate immune system
The innate immune system is the part of our immunity passed on by our mother at birth. The cells in our innate immune system are the first responders, not specifically tailored to any particular type of pathogen. They respond quickly and efficiently to a wide range of invaders.
The innate immune system is also the second line of defence and is activated once a pathogen breaches our skin or mucous membranes. The innate immune system consists not only of phagocytes and natural killer cells but also of signalling substances. The function of these signalling substances is to activate and subsequently regulate 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 activates when the innate immune system cannot completely eliminate the invader. This system responds more slowly but has the ability to adapt to specific invaders, remember them, and recognise them during a potential future infection. The adaptive immune system consists of various 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 in combating 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 its so-called immunological memory. This means that after an initial infection, the adaptive immune system develops a recognition mechanism to combat the invader more quickly and efficiently during a subsequent infection.
The different types of white blood cells
White blood cells are the leaders of our health army. As explained above, white blood cells are the first to respond when an invader appears. There are different types of white blood cells, which can be divided into phagocytes and lymphocytes.
Phagocytes
Phagocytes include macrophages, neutrophils, monocytes, dendritic cells, and mast cells. This type of white blood cell constantly searches for viruses, dead cells, and other pathogens through our blood vessels and tissues. They are an essential part of our innate immune system, generating a non-specific immune response against pathogens. When a phagocyte discovers a foreign organism, it immediately engulfs it through a process called phagocytosis (engulfment). Once engulfed, the pathogen is digested and neutralised.
Lymphocytes
Lymphocytes are small white blood cells defending the body against pathogens, foreign substances, and tumour cells. Lymphocytes include T cells, B cells, and natural killer cells. They primarily 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 known as the adaptive immune system.
How can I boost my immunity?
The health of our immunity not only determines how well we withstand seasonal illnesses but also how quickly we recover. To keep your immune system in good condition, it's essential to take care of yourself. Adequate rest, good sleep, spending time outdoors daily, a healthy diet rich in vitamins C, D, zinc, and antioxidants, regular exercise, and reducing stress are all crucial factors for a well-functioning immune system. Supporting your gut can also make a significant difference. In this blog, you can read more about how healthy intestines contribute to strong immunity.
