The immune system is the body’s defence against infections. The immune (ih-MYOON) system attacks germs and helps keep us healthy.

The role of the immune system — a collection of structures and processes within the body — is to protect against disease or other potentially damaging foreign bodies. When functioning properly, the immune system identifies a variety of threats, including viruses, bacteria and parasites, and distinguishes them from the body’s own healthy tissue, according to Merck Manuals.

How Does the Immune System Work?

When the body senses foreign substances (called antigens), the immune system works to recognize the antigens and get rid of them.

B lymphocytes are triggered to make antibodies. These specialized proteins lock onto specific antigens. The antibodies stay in a person’s body. That way, if the immune system encounters that antigen again, the antibodies are ready to do their job. That’s why someone who gets sick with a disease, like chickenpox, usually won’t get sick from it again.

This is also how immunizations (vaccines) prevent some diseases. An immunization introduces the body to an antigen in a way that doesn’t make someone sick. But it does let the body make antibodies that will protect the person from future attack by the germ.

Although antibodies can recognize an antigen and lock onto it, they can’t destroy it without help. That’s the job of the T cells. They destroy antigens tagged by antibodies or cells that are infected or somehow changed. (Some T cells are actually called “killer cells.”) T cells also help signal other cells (like phagocytes) to do their jobs.

Antibodies also can:

• neutralize toxins (poisonous or damaging substances) produced by different organisms
• activate a group of proteins called complement that are part of the immune system. Complement helps kill bacteria, viruses, or infected cells.

These specialized cells and parts of the immune system offer the body protection against disease. This protection is called immunity.

Innate and adaptive immunity

The immune system can be broadly sorted into categories: innate immunity and adaptive immunity.

Innate immunity is the immune system you’re born with, and mainly consists of barriers on and in the body that keep foreign threats out, according to the National Library of Medicine (NLM). Components of innate immunity include skin, stomach acid, enzymes found in tears and skin oils, mucus and the cough reflex. There are also chemical components of innate immunity, including substances called interferon and interleukin-1.

Innate immunity is non-specific, meaning it doesn’t protect against any specific threats.

Adaptive, or acquired, immunity targets specific threats to the body, according to the NLM. Adaptive immunity is more complex than innate immunity, according to The Biology Project at The University of Arizona. In adaptive immunity, the threat must be processed and recognized by the body, and then the immune system creates antibodies specifically designed to the threat. After the threat is neutralized, the adaptive immune system “remembers” it, which makes future responses to the same germ more efficient.

Major components

Lymph nodes: Small, bean-shaped structures that produce and store cells that fight infection and disease and are part of the lymphatic system — which consists of bone marrow, spleen, thymus and lymph nodes, according to “A Practical Guide To Clinical Medicine” from the University of California San Diego (UCSD).

Spleen: The largest lymphatic organ in the body, which is on your left side, under your ribs and above your stomach, contains white blood cells that fight infection or disease. 

Bone marrow: The yellow tissue in the center of the bones produces white blood cells. This spongy tissue inside some bones, such as the hip and thigh bones, contains immature cells, called stem cells, according to the NIH. Stem cells, especially embryonic stem cells, which are derived from eggs fertilized in vitro (outside of the body), are prized for their flexibility in being able to morph into any human cell. 

Lymphocytes: These small white blood cells play a large role in defending the body against disease, according to the Mayo Clinic. The two types of lymphocytes are B-cells, which make antibodies that attack bacteria and toxins, and T-cells, which help destroy infected or cancerous cells. 

Thymus: This small organ is where T-cells mature. This often-overlooked part of the immune system, which is situated beneath the breastbone (and is shaped like a thyme leaf, hence the name), can trigger or maintain the production of antibodies that can result in muscle weakness, the Mayo Clinic said.

Leukocytes: These disease-fighting white blood cells identify and eliminate pathogens and are the second arm of the innate immune system. A high white blood cell count is referred to as leukocytosis, according to the Mayo Clinic.

Healthy ways to strengthen your immune system

Your first line of defence is to choose a healthy lifestyle. Following general good-health guidelines is the single best step you can take toward naturally keeping your immune system strong and healthy. Every part of your body, including your immune system, functions better when protected from environmental assaults and bolstered by healthy-living strategies such as these:

• Don’t smoke.
• Eat a diet high in fruits and vegetables.
• Exercise regularly.
• Maintain a healthy weight.
• If you drink alcohol, drink only in moderation.
• Get adequate sleep.
• Take steps to avoid infection, such as washing your hands frequently and cooking meats thoroughly.
• Try to minimize stress.

Exercise: Good or bad for immunity?

Regular exercise is one of the pillars of healthy living. It improves cardiovascular health, lowers blood pressure, helps control body weight, and protects against a variety of diseases. But does it help to boost your immune system naturally and keep it healthy? Just like a healthy diet, exercise can contribute to general good health and therefore to a healthy immune system. It may contribute even more directly by promoting good circulation, which allows the cells and substances of the immune system to move through the body freely and do their job efficiently.

Some scientists are trying to take the next step to determine whether exercise directly affects a person’s susceptibility to infection. For example, some researchers are looking at whether extreme amounts of intensive exercise can cause athletes to get sick more often or somehow impairs their immune function. To do this sort of research, exercise scientists typically ask athletes to exercise intensively; the scientists test their blood and urine before and after the exercise to detect any changes in immune system components. While some changes have been recorded, immunologists do not yet know what these changes mean in terms of human immune response.