The Immune System and Its Link to Rheumatic Disease

The immune system allows us to identify and destroy foreign invaders (bacteria, viruses, fungi, etc.) and survey our own cells to prevent them from growing uncontrollably (tumors, cancers, etc.). The complexity and capability of the immune system to protect us is astounding.

The immune system can be divided into two components: the innate (born with) immune system and adaptive (develop through life) immune system. The innate component is the first line of defense. It reacts very quickly to fight off things that are foreign to the body such as viruses and bacteria and identifying damaged cells. Cells of the innate immune system try to destroy the foreign intruders by attacking them and releasing toxic molecules. It also releases other signals to recruit more inflammatory cells to join the fight.

The adaptive component is slower to react taking several days to activate T cells, B cells, and make antibodies to fight off foreign invaders. It develops as we age and is built up by vaccines. The adaptive immune system also produces antibodies that remember the foreign invader so that the immune system can recognize foreign invaders quicker in the future.

There are times, however, when the immune system gets confused. It can no longer distinguish your own good tissue from harmful foreign invaders. It mistakenly directs inflammation against your own tissue causing damage and disease. This damage can occur in your joints, muscles, blood vessels, kidneys, and virtually any tissue in your body. Illnesses from this type of damage are called autoimmune (self- immune) diseases. They include rheumatoid arthritis, systemic lupus, and vasculitis to name a few.

Why this happens is not entirely clear. In some of these illnesses, the blood vessels are innocent bystanders. As our bodies are fighting a virus (e.g., Hepatitis C), we form antibodies against the virus. The antibodies and virus particles get stuck together and get deposited into the walls of the blood vessels creating inflammation. This can result in activation of the immune system that can cause inflammation, damage, and narrowing of blood vessels which can go on to cut off blood supply causing even more damage.

Another cause of autoimmune (self-immune) disease is genetics. Patients with a gene called HLA-DR4 have an increased risk of developing rheumatoid arthritis. This is a blood test but it is not typically run as it can be nonspecific. For example, some patients have this gene but never develop rheumatoid arthritis. We have learned through much research that genetics are only part of the story. Environmental stimuli (such as viruses and smoking) can also influence the immune system to react in an unhelpful way to cause autoimmune disease instead of protecting your body. It typically takes both the right genes and environmental exposures together to lead your immune system towards an autoimmune (self-immune) state.

Similar processes occur in systemic lupus erythematosus. The genetic background, as well as particular environmental exposures, creates a situation where that individual patient has an increased risk for developing one of these illnesses.

Autoimmune diseases can be very difficult to diagnose, and the right treatment must be carefully chosen for the right disease at the right time. Each diagnosis requires a thorough history and physical exam, and often many laboratory tests. Frequently, involvement of a specialist, known as a rheumatologist, is needed.

A rheumatologist has additional training in the diagnosis and management of autoimmune diseases. In addition to the above workup, the rheumatologist may order special tests. For example, if vasculitis is suspected, the rheumatologist may order a biopsy of the skin or another part of the body.

The key component of all of these diseases involves our own immune system, which contributes to the illness. So therapy targeting our own immune system can help alleviate the diseases themselves.

If treatment is required, the drugs used may include medications that fight inflammation very quickly (e.g. steroids), oral medications that change the course of the disease over time (e.g. methotrexate), or even newer biologic medications which change or disable parts of the immune system responsible for the autoimmune disease (e.g. TNF inhibitors, IL-6 inhibitors, etc).

These drugs suppress the immune system, so careful monitoring of side effects is essential. Only a physician experienced with these drugs and diseases, such as a rheumatologist, should monitor the therapies.

New biologic therapies are directed against the small molecules which orchestrate our own immune response. These drugs include tumor necrosis factor inhibitors (TNF), IL-6 inhibitors, inhibitors of T cell and B cell interaction, and others.

By using specific targeted therapy against specific messengers, we can change our immune response, both for the good and for the bad. Any change in the immune system may control the disease, but may also subject us to different risks such as infection that need to be monitored by your rheumatologist.