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Immune System and Disorders
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Immune System

Immune System and Disorders

The immune system acts as the body's primary defense network, utilizing a complex array of cells and organs to identify and neutralize harmful substances.

What is the immune system?

Your immune system is a complex network of cells, tissues, and organs. Together, they help the body fight infections and other diseases. When germs such as bacteria or viruses invade your body, they attack and multiply, causing an infection. Your immune system protects you by fighting off these germs.

Parts of the Immune System

The immune system includes several protective components:

  • Skin: Acts as a barrier to prevent germs from entering the body.
  • Mucous membranes: Moist, inner linings of organs and cavities that produce mucus to trap and fight germs.
  • White blood cells: Specialized cells that actively fight germs.
  • Lymph system: Includes the thymus, spleen, tonsils, lymph nodes, lymph vessels, and bone marrow, which produce, store, and carry white blood cells.

How the Immune System Works

The immune system defends the body against antigens—substances recognized as harmful or foreign, such as germs, toxins, or damaged cells. When the immune system detects an antigen, it initiates an immune response, which includes the production of antibodies. These proteins attack, weaken, and destroy the antigens. Once the system encounters an antigen, it "remembers" it, allowing for a faster response if the same threat returns, a process known as immunity.

Types of Immunity

  • Innate immunity: Protection you are born with, including physical barriers like skin and mucous membranes.
  • Active immunity: Also called adaptive immunity, this develops after an infection or vaccination and is typically long-lasting.
  • Passive immunity: Occurs when you receive antibodies from an outside source, such as maternal antibodies in newborns or blood products. This provides immediate but temporary protection.

Immune System Disorders

Problems arise when the immune system malfunctions:

  • Autoimmune diseases: The immune system mistakenly attacks healthy cells.
  • Allergies and Asthma: The immune system reacts to harmless substances as if they were threats.
  • Immunodeficiency diseases: The system does not work correctly, making the body more susceptible to frequent, serious, or long-lasting infections. These are often genetic.
  • HIV/AIDS: HIV is a virus that destroys white blood cells. If untreated, it can lead to AIDS (acquired immunodeficiency syndrome), resulting in a severely damaged immune system and increased vulnerability to illness.

Frequently Asked Questions

Frequent infections can be a sign that the immune system is not functioning optimally. You should consult a healthcare provider if you experience more than two sinus infections, four ear infections, or two or more courses of antibiotics in a year, or if you have a lung infection that takes more than four weeks to clear. Other warning signs include chronic diarrhea, poor weight gain in children, or recurrent skin abscesses. These patterns suggest that your body may not be producing enough white blood cells or antibodies to effectively neutralize pathogens.
ctive immunity develops when your body produces its own antibodies after fighting an infection or receiving a vaccine. This type of immunity is typically long-lasting, often lasting for years or a lifetime, because your immune system retains a memory of the pathogen. Passive immunity, on the other hand, occurs when you receive pre-made antibodies from an outside source, such as through maternal antibodies passed to a newborn or through a medical injection for immediate protection. Passive immunity provides quick, short-term protection that fades as the antibodies break down, usually within a few weeks to months, and does not create long-term immune memory.
Vaccines introduce a harmless version of a pathogen, such as a weakened virus, a piece of the virus, or a protein from the virus, into the body. This triggers the immune system to recognize the threat and produce antibodies and memory cells, just as it would during a real infection. However, because the vaccine does not contain the live, disease-causing agent, you do not get sick. Instead, your immune system is "trained" to respond quickly and effectively if you encounter the real pathogen in the future.
Mucous membranes line the nose, mouth, lungs, and digestive tract, acting as a physical barrier that traps dust, bacteria, and viruses in mucus. They also contain immune cells that can detect and fight off invaders before they penetrate deeper into the body. To keep them healthy, you should stay well-hydrated, as dry membranes are less effective at trapping pathogens. Avoiding smoking and excessive alcohol consumption is also crucial, as these irritants can damage the mucosal lining and impair its protective functions.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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