Wegener’s Granulomatosis is an auto-immune disease, but what is the immune system and how does it work?

The immune system is the body’s defence mechanism against invasion from infection and disease. It defends you against germs and micro-organisms using a network of special cells, tissues, proteins and organs. White blood cells, or leukocytes, try to seek out and destroy disease-causing organisms and substances. White blood cells are stored and produced in many different parts of the body. such as the thymus, spleen and in the bone marrow. Lymph nodes across the body also house these leukocytes.

These white blood cells circulate throughout the body in the blood and lymphatic vessels to form a co-ordinated response to disease.

The two basic types of white blood cells are phagocytes, cells that chew up invading organisms, and lymphocytes, which are cells that allow the body to remember and recognise previous invaders and help the body destroy them.

The most common type of phagocyte is neutrophil, which primarily attacks bacteria. Other types of phagocytes attack their own specific invader. I explained how the neutrophils inside Wegener’s Disease sufferers are affected in this previous blog post.

There are two types of lymphocytes – B cells and T cells. The lymphocytes cell start in the bone marrow. If they remain there then they become B cells. If they leave the bone marrow and travel to the thymus gland they become T cells. The B cells seek out infection and send the bodies other defences to attack the source. The T cells can then destroy the targets identified by the B cells.

When an antigen, a hostile foreign substance, is found in the body, is detected, several types of cells work together to identify the threat. The B cells then tell the body to produce antibodies, specialised  proteins lethal to particular antigens.

Once these antibodies are produced they stick around the body waiting to fight against any further infection. That is why you usually only contract diseases such as chickenpox once. In second and subsequent infections the antibodies are ready and waiting to attack the antigen before it can gain a foothold.

This is how vaccinations work. The immunisation encourages the body to produce the antibodies without giving you the disease. This protects the body against further attack from that particular type of organism or substance.

The antibodies don’t actually destroy the target antigens. That is the job of the T cells. The T cells also alert other cells, such as the phagocytes, to do their jobs.

Antibodies can neutralise toxins from lots of different organisms and can activate a group of proteins called complement. Complement assist the body to kill bacteria, viruses and infected cells.

This whole interconnected process is called the immune system.

Types of Immunity

People have three different types of immunity – innate, adaptive and passive.

Virtually everyone is born with innate immunity. Many of the viruses which affect animals won’t affect humans and vice versa. Dogs cannot contract HIV and the viruses which cause leukemia in cats cannot affect humans. Innate immunity also includes the skin and mucous membranes (such as the nose, throat and intestines). This is the body’s first line of defense against disease. The body will try to repair any damage to it’s innate immunity. If the skin is cut, for example, the body will try to heal the wound and send special cells to the cut to fight off any germs.

Inflammation is one of the immune system’s first responses to infection. Blood flow to the area is increased which leads to redness, swelling, heat and pain. Cytokines and other chemicals recruit immune cells to the site of the infection to heal damaged tissue following the removal of any pathogens (a living agent which causes disease).

Adaptive immunity develops over time, as the body is exposed to various infections and diseases. This is one of the reasons why adults tend to get fewer colds than kids – their bodies have produced antibodies which fight off lots of types of viruses which cause colds.

Passive immunity generally last for a short period of time as it is ‘borrowed’ from another source. A good example is breast milk, which passes antibodies from the mother to the child. This helps the child fight off infection in their early life, perhaps for as long as a few months.

Immune Disorders

There are four main disorders of the immune system:

  • Immunodeficiency disorders (primary or acquired)
  • Autoimmune disorders (in which the body’s own immune system attacks its own tissue as foreign matter)
  • Allergic disorders (in which the immune system overreacts in response to an antigen)
  • Cancers of the immune system

Immunodeficiency disorders occur when part of the immune system is missing or inactive, from a genetic disease for example . IgA deficiency is the most common example of this, where the body does not produce enough IgA antibodies in the saliva and other bodily fluids. People with IgA deficiency tend to get more colds and respiratory disease than others but the condition is usually not severe.

Acquired immunodeficiencies normally occur after disease or injury. HIV is one such example which attacks the T helper cells. This leaves the body powerless to attack normally harmless organisms. Some medications cause immunodeficiencies as a side effect. Malnutrition is the greatest cause of immunodeficiency in the developing world while obesity, alcoholism and drug use contribute to immunodeficiency in the developed world.

In autoimmune disorders the body’s own immune system mistakenly attacks itself. Wegener’s Granulomatosis is of course one such example. Other examples are lupus or ankylosing spondylitis. It is believed that there is a genetic component to GPA which is then triggered by an environmental factor.

Allergic disorders occur when the body overreacts to an antigen. The substances that cause this reaction are called allergens. The hyperactive immune response can cause symptoms such as swelling, sneezing, watering eyes or even anaphylaxis. Antihistamines are used to combat the symptoms. Asthma and eczema are the two most common allergic disorders. Food allergies (nuts) and insect stings (wasps and bees) are also common.

Finally, cancer occurs when cells grow out of control. Leukaemia, for example, is the abnormal growth of leukocytes and lymphoma is cancer of the lymphoid tissues.

Immune system disorders cannot normally be prevented, but they can be managed with the right treatment.

Many of the treatments of Wegener’s Granulomatosis bring relief by trying to get the inflammation under control. Drugs such as Prednisone, cyclophosmamide and Rituximab all seek to inhibit the body’s inappropriate immune response. However, as I have just demonstrated, the immune system is vital to your general health and unfortunately all of the drugs currently used to treat Wegener’s Disease will also reduce the body’s ability to fight off other diseases. We can only hope that the side effects of the drugs used to treat Wegener’s continue to improve and their effects on the immune system in general lessen.

Image provided by Andrew Mason via Creative Commons.