Immune system – the primary defense mechanism

The immune system is a complex biological system. In fact, after the human brain, it is one of the most complex systems.¹ It constantly protects the body against infections and diseases. That’s why it’s important to understand how it works and why to take good care of it.

How does the immune system work?

The immune system is the primary defense mechanism that constantly protects the body against viruses and bacteria, especially during the cold and flu season.2 That's why it's essential to give the immune system the care it needs – so that, in return, it can take care of the body. The immune system is incredibly complicated and utterly vital for survival. Several different systems and cell types work in perfect synchrony throughout the body. Immune organs, tissues, cells, and molecules are interconnected to fight off pathogens and clear up dead cells. External threats include germs such as bacteria, viruses, fungi, and toxins.3 If the immune system is doing its job correctly and runs smoothly, we don't even notice it's there. However, if the immune system is compromised due to deficiency or an aggressive form of bacteria or virus, the body reacts with illness.4

When a pathogen enters the body, the immune system recognizes foreign molecules, so called antigens immediately, and a series of processes are triggered. The so-called B lymphocytes make antibodies, and these proteins lock onto the antigens, to mark them. Other cells, such as the phagocytes, remove or inactivate the unknown pathogens. After the immune system has successfully neutralized the antigens, the body usually stores information about the antigen – how to recognize it later again and fight it faster.5

The main parts of the immune system are:

  • White blood cells

    White blood cells are front and center when it comes to immune response. They are made in the bone marrow and circulate in the blood and lymphatic tissues where they look for pathogens and potentially launch an immune response.6

  • Antibodies

    Antibodies help fight microbes and the toxins by recognizing antigens and marking them for destruction.2

  • Complement system

    The complement system consists of various proteins that help promote inflammation and enhance immune responses by helping the antibodies complete their task.2

  • Lymphatic system

    The lymphatic system also plays a vital role. As a network of delicate tubes throughout the body, it manages fluid levels, and reacts to various pathogens in the body. The lymphatic system consists of lymph nodes, lymph vessels, and white blood cells (lymphocytes).7

  • Spleen

    The spleen removes microbes and destroys old or damaged red blood cells. As a blood-filtering organ, it also makes disease-fighting components of the immune system.2

  • Bone marrow

    Bone marrow is the spongy tissue inside the bones, which produces the oxygen-carrying red blood cells, the infection-fighting white blood cells, and the blood-clotting platelets.2

  • Thymus

    This small organ helps to mature and “train” T-cells, a specific type of white blood cell, before they start circulating in the body.2

Two different immune responses

The immune system consists of immune organs, tissues, cells, and molecules that are interconnected to fight off external or internal threats. There are two main types of immune responses: innate immunity and adaptive immunity, and both are essential for health and survival:

The innate immune system

Humans and animals are born with the innate immune system. Its primary purpose is to prevent the spread of harmful agents by attacking them with cells such as scavenger cells called phagocytes (or macrophages) and releasing numerous molecules (e.g., signaling molecules, antiviral compounds) that further assist and regulate the innate immune response. The innate immune system is the first to respond when it finds an invader. The line of defense includes the skin, the eye's cornea, and the mucous membrane that lines the respiratory, gastrointestinal, and genitourinary tracts. These physical barriers protect the body against harmful germs and parasites. If the pathogen manages to pass the innate immune system, the adaptive immunity kicks in.8

The adaptive immune system

The adaptive immune system develops during its lifetime in response to exposure to infections and toxins. It helps recognize and kill harmful agents by producing unique proteins called antibodies. These antibodies are made by B lymphocytes cells after the body has been exposed to the intruder. The adaptive immune system is constantly learning and adapting, and therefore, the body can also fight bacteria or viruses that change over time. It builds up a library of antibodies to different pathogens, called immunological memory.9

Both parts of the immune system are interconnected and play a critical role in defense against infections.

The effects of a strong immune system

The immune system is a highly complex network of organs, cells, and molecules that researchers are still working to understand. However, the reasons for having a strong immune system speak for themselves.

Fewer sick days

A well-functioning immune system may help the body respond more effectively to viruses and bacteria, which may be associated with a reduced risk of infections and illness-related absence.10

Less medication*

Especially during the flu season, most people tend to take synthetic medication to fight off colds. But unlike natural medicine, synthetic medications are often accompanied by various side effects.11

Milder symptoms

An effective immune response may contribute to a more efficient recovery from common infections and may be associated with milder or shorter-lasting symptoms.10

Better for the body

Both the innate and the adaptive immune responses need to be well balanced. An effective immune system relies on a regulated immune response to successfully eliminate viral infections without harming the body.

* A well-functioning immune system may support recovery, but medication may still be necessary depending on symptom severity and medical advice. 

How to strengthen the immune system?

For the immune system to work correctly, it needs to rely on balance and harmony. Researchers are still exploring the intricacies of the immune response and what exactly may strengthen it. At present, there is limited direct scientific evidence that individual lifestyle measures can specifically ‘boost’ immune function. However, healthy lifestyle behaviors are associated with overall health and normal immune system function.12
 

  • REGULAR EXERCISE

    Regular exercise improves cardiovascular health, lowers blood pressure, helps control body weight, and protects against various diseases. In other words, it contributes directly to general good health and therefore to a healthy immune system.13

  • HEALTHY LIFESTYLE

    A part of a healthy lifestyle is refraining from certain things. Excessive alcohol consumption, for example, can have numerous adverse effects on the body. The same goes for smoking, which weakens the immune system, making the body more susceptible to bacterial and viral infections.2

  • STRESS MANAGEMENT

    Stress can be good, but if the body has no time to recuperate and the strain continues, stress can even suppress the immune system, increasing susceptibility to colds and other illnesses.14

  • BALANCED DIET

    Poor nutrition can have a negative effect on the immune system. Therefore, a balanced diet is good for the body, and it includes fruits and vegetables that are rich in vitamins and minerals. Certain vitamins, including vitamins A, C, D, and E contribute to normal immune system function and overall health.15

  • SUFFICIENT SLEEP

    The body needs sleep to fight off infectious diseases, and sleep deprivation reduces the production of infection-fighting antibodies and cells. And in addition, long-term lack of sleep increases the risk of obesity, diabetes, and cardiovascular disease.16

Pharmacological approach

Most mild viral respiratory illnesses are managed symptomatically. A growing number of people rely on natural medications that have a good safety profile and are well tolerated in a broad range of patient types. Plant-based medications with natural ingredients from the pharmacy can help with viral infections and common colds by supporting the defense system of the body, without the need for a prescription. They can help your immune system respond more effectively.17,18

Heel natural medicines

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  2. Cleveland Clinic. Immune System Function, Conditions & Disorders. My Cleveland Clinic. 2025. Available from: https://my.clevelandclinic.org/health/body/21196-immune-system/. Accessed Dec 16, 2025.
  3. Tuhin M. What is the Immune System? How Your Body’s Defense Works to Keep You Alive. Science News Today. 2025 Apr 13. Available from: https://www.sciencenewstoday.org/what-is-the-immune-system-how-your-bodys-defense-works-to-keep-you-alive/. Accessed Jan 05, 2026.
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