In biology, immunity is the balanced state of multicellular organisms having adequate biological defences to fight infection, disease, or other unwanted biological invasions, while having adequate tolerance to avoid allergy and autoimmune diseases.
The immune system is found in:
- White blood cells are the key players in your immune system. They are made in your bone marrow and are part of the lymphatic system. White blood cells move through blood and tissue throughout your body, looking for foreign invaders (microbes) such as bacteria, viruses, parasites, and fungi. When they find them, they launch an immune attack.
- Antibodies help the body to fight microbes or the toxins (poisons) they produce. They do this by recognizing substances called antigens on the surface of the microbe. The antibodies then mark these antigens for destruction.
- The complement system is made up of proteins whose actions complement the work done by antibodies.
- The lymphatic system is a network of delicate tubes throughout the body. The main roles of the lymphatic system are to:
- manage the fluid levels in the body
- react to bacteria
- deal with cancer cells
- deal with cell products that otherwise would result in disease or disorders
- absorb some of the fats in our diet from the intestine.
- The spleen is a blood-filtering organ that removes microbes and destroys old or damaged red blood cells. It also makes disease-fighting components of the immune system (including antibodies and lymphocytes).
- Bone marrow is the spongy tissue found inside your bones. It produces the red blood cells our bodies need to carry oxygen, the white blood cells we use to fight infection, and the platelets we need to help our blood clot.
- The thymus filters and monitors your blood content. It produces the white blood cells called T-lymphocytes.
There are two main parts of the immune system:
- The innate immune system: The evolutionary older innate immune system provides a general defence against pathogens, so it is also called the nonspecific immune system. It works mostly at the level of immune cells like “scavenger cells” or “killer cells.” These cells mostly fight against bacterial infections.
- The adaptive immune system: In the adaptive immune system, particular agents like the so-called antibodies target very specific pathogens that the body has already had contact with. That is why this is also called a learned defence or a specific immune response. By constantly adapting and learning the body can also fight against bacteria or viruses that change over time.
Common disorders of the immune system
Over-activity of the immune system can take many forms, including:
- Allergic diseases – where the immune system makes an overly strong response to allergens. Allergic diseases are very common. They include allergies to foods, medications or stinging insects, hay fever (allergic rhinitis), sinus disease, asthma, hives (urticaria), dermatitis and eczema.
- Autoimmune diseases – where the immune system mounts a response against normal components of the body. Autoimmune diseases range from common to rare. They include multiple sclerosis, autoimmune thyroid disease, type 1 diabetes, rheumatoid arthritis, and systemic vasculitis.
Under-activity of the immune system, can:
- Be inherited – examples of these conditions include primary immunodeficiency diseases such as common variable immunodeficiency (CVID), x-linked severe combined immunodeficiency (SCID) and complement deficiencies.
- Arise as a result of medical treatment – this can occur due to medications such as corticosteroids or chemotherapy.
- Be caused by another disease – such as HIV/AIDS or certain types of cancer.
An underactive immune system does not function correctly and makes people vulnerable to infections. It can be life-threatening in severe cases.
People who have had an organ transplant need immunosuppression treatment to prevent the body from attacking the transplanted organ.
This blog provides general information and discussions about health and related subjects. The information and other content provided in this blog, or in any linked materials, are not intended and should not be construed as medical advice, nor is the information a substitute for professional medical expertise or treatment. If you or any other person has a medical concern, you should consult with your health care provider or seek other professional medical treatment. Never disregard professional medical advice or delay in seeking it because of something that has read on this blog or in any linked materials. If you think you may have a medical emergency, call your doctor or emergency services immediately.