Crohn’s disease is a type of inflammatory bowel disease (IBD). It causes inflammation in the digestive system, and the inflammation and ulcers may occur anywhere in the digestive system and other parts of the body, including joints, skin, and eyes.
Scientists do not know what causes Crohn’s disease, but it appears to be hereditary with an environmental inducement. And, there is some debate about how to classify Crohn’s disease. As researchers conduct more studies into the causes of IBD, understanding will improve. This advancement should lead to better treatment and individualized therapeutics.
Crohn’s disease does not result in the creation of antibodies. Therefore, calling the condition an “autoimmune” disorder is inaccurate. Instead, researchers are referring to Crohn’s as an immune-mediated condition or an autoinflammatory condition.
What is an autoimmune disease?
The immune system is a key factor in the body’s defense system. It mitigates or prevents infections and diseases caused by pathogens, bacteria, viruses, parasites, and fungi. It does this by learning how to attack the foreign invader.
However, when the immune system malfunctions, autoimmune conditions can develop. Scientists who study the immune system have several hypotheses. One is that an event triggers an adaptive immune system into action. It learns how to target specific invaders that carry disease. On occasion, the immune system may interpret its own body’s cells as invaders and attack them. The dysfunctional immune system targets healthy tissue and causes disease.
When the immune system responds in such an inappropriate way, it leads to a chain reaction that encourages the creation of antibodies against the person’s own cells. These are known as autoantibodies.
The autoantibodies play a crucial role in causing the inflammation associated with autoimmune disorders. Doctors will sometimes treat autoimmune conditions with medications that suppress some of the immune system. Still, not everyone who has autoantibodies develops an autoimmune disorder.
Scientists have identified over 80 autoimmune diseases including rheumatoid arthritis, celiac disease, myasthenia gravis, and Kawasaki disease. However, they have not been able to identify an antibody associated with Crohn’s whereas they have identified antibodies for the other disorders.
Many autoimmune disorders are chronic and must be treated long-term, sometimes for life. Some disorders can be self-limiting or don’t require a lifetime of management when treated effectively.
What is an autoinflammatory disease?
The human body also has an innate immune system, which is controlled by genes inherited from your parents. It is the first defense against a pathogen or other harmful substance. It springs into action quickly causing symptoms like fever, heat, and swelling. The genes that encode the innate immune system can undergo certain alterations, which will impact how the immune system reacts.
In some circumstances, this alteration may mean that the innate immune system cannot be differentiated between pathogens and healthy tissue. When the innate immune system identifies healthy body cells as harmful invaders, it goes on the offensive and causes inflammation.
The inflammation caused by the innate immune system acting in this way can occur throughout the body, which is called a systemic response. This inflammatory response can become chronic.
Crohn’s and the gut microbiome
Another factor that may contribute to the development of Crohn’s disease is the gut microbiome. The microbiome is the collection of microorganisms living in your digestive tract. People with Crohn’s disease have an unhealthy balance between good and bad bacteria in the gastrointestinal tracts (GI) in contrast to individuals without the disease.
The complexity of the gut microbiome makes it difficult to fully understand. The issues go beyond an imbalance of just one or two bacteria. When this dysbiosis is chronic, it may be one factor leading to the development of Crohn’s disease.
However, researchers are beginning to identify some trends in the alterations of the gut microbiome in individuals with Crohn’s disease. This will help with the development of treatments, although it’s clear that not every case of Crohn’s affects the microbiome the same way.
Genetics, Crohn’s, and autoinflammatory disease
Scientists have identified a genetic component to Crohn’s disease just like IBD. Hundreds of genes are linked to various forms of IBD. This means that Crohn’s may be inherited, although not everyone with the genes will develop the disease. In fact, most people with Crohn’s have no other relatives with the disease.
While alterations in the genetics of the innate immune system have a role in Crohn’s disease, there are other factors. There is an environmental trigger as well that induces the innate immune system to begin the inflammation and not stop. There may also be environmental triggers that contribute to IBD.
According to Marla Dubinsky, MD, director of the Pediatric Inflammatory Bowel Disease Center at Cedars-Sinai Medical Center and associate professor of pediatrics at Cedars-Sinai Medical Center, “IBD actually fits into the category of autoinflammatory conditions, which is distinct from an autoimmune condition.”
Dr. Dubinsky says that in Crohn’s disease, “…the innate immune system becomes confused and causes inflammation without threats being present.” Without that autoantibody piece, Crohn’s disease can’t be placed into the autoimmune disease category.
Crohn’s disease affects the digestive tract, but other body systems are affected as well. This is another factor that points to it being a systemic innate immune system-related disorder. It is common for people with Crohn’s disease to develop other conditions caused by an inflammatory response.
According to Dr. Dubinsky, “While a specific body system might be mainly affected, like the GI tract in Crohn’s disease, the nonspecific nature of the innate immune system means that other systems are inevitably affected as well.”
Other diseases associated with Crohn’s
People who live with Crohn’s disease may also have other conditions, especially those that are immune-mediated. Some of the related conditions may have a similar inflammatory pathway as Crohn’s disease.
The issues with the immune system that result in IBD may also trigger other immune-mediated conditions. The risk of developing another condition is dependent on man factors like age, gender, ethnicity, severity, and the type of IBD.
Some of the common inflammatory conditions that may occur in people with Crohn’s include primary sclerosing cholangitis, episcleritis, iritis, psoriasis, pyoderma gangrenosum, and ankylosing spondylitis.
Triggers
The exact causative factor of the development of Crohn’s disease is unknown, but scientists believe several different factors contribute. First, there is the genetic component, with hundreds of genes associated with the disease. Then, there is the environmental factor, which can result in an inflammatory loop that attacks the digestive tract and other body systems.
Environmental triggers may include:
- Air pollution
- Appendectomy
- Diet
- Exposure to heavy metals
- Living in an urban area
- Medications
- Physical activity level
- Smoking (and secondhand smoke)
- Stress
- Sleep
- Vitamin D levels
Researchers have not determined the extent to which any of these triggers may be involved in a specific case of Crohn’s. And, they need to do further research to understand how the microbiome interacts with external triggers that lead to Crohn’s.
Some research shows that people with IBD have fewer species of bacteria in their microbiomes. That diversity may contribute to Crohn’s.
Categorizing Crohn’s disease
Researchers still debate how to categorize Crohn’s disease. Previously, scientists believed it was an autoimmune condition, but not anymore. Crohn’s is more accurately described as autoinflammatory.
Some research hypothesizes that IBD is the result of an immune deficiency. Researchers point to a defect within the white cells of people who live with an IBD. However, that hypothesis is less accepted now and does not adequately describe Crohn’s.
The immune system does have a role in the development of Crohn’s disease. And, Crohn’s may be comprised of many different disorders. This could mean that there are different varieties of Crohn’s along a spectrum.
In some cases, Crohn’s disease and IBD are also referred to as “immune-mediated” conditions. This is a broader term that encompasses all the conditions related to the dysregulation of the immune system. As more research is completed, the understanding of what causes IBD will improve, leading to better treatments and individualized medicine.
Other autoimmune disorders associated with Crohn’s
Some of the inflammatory and autoimmune conditions that are most often found in people who live with IBD include:
- Ankylosing spondylitis
- Asthma
- Atrophic gastritis
- Autoimmune hepatitis
- Celiac disease
- Churg Strauss syndrome
- Episcleritis
- Giant cell arteritis
- Graves’ disease
- Iridocyclitis (also called iritis or uveitis)
- Polyarteritis nodosa
- Polymyalgia rheumatica
- Primary biliary cholangitis
- Primary sclerosing cholangitis
- Psoriasis
- Psoriatic arthritis
- Pyoderma gangrenosum
- Rheumatoid arthritis
- Sarcoidosis
- Type 1 diabetes
Final thoughts
Crohn’s disease is not an autoimmune disease because people with the condition don’t have antibodies that target their own bodies. Scientists are conducting more studies to understand Crohn’s, its causes, and how it should be classified. Currently, researchers call Crohn’s an immune-mediated condition or an autoinflammatory condition.
We still need to have more insight into Crohn’s disease, and studies are beginning to peel back the layers to pinpoint the causes.
Crohn’s disease may develop when the immune system is trying to respond to a threat, but there isn’t any threat present. This leads to inflammation that targets the digestive system but also can affect the rest of the body.
However, it is not an autoimmune response because antibodies are not found in Crohn’s disease. It may be more correct to call Crohn’s disease an immune-mediated disease or an autoinflammatory disease.