Asthma Subgroups: Th2 Dominant Asthma
About 10% of the world’s population has a diagnosis of asthma. This means they have asthma genes. And these asthma genes are activated. About 50% of these asthmatics have Th2 dominant asthma. So, what is this? Here’s all you need to know.
What is a little history here?
Right after the turn of the 20th-century allergies were discovered. This is evidenced by the fact that the term allergy was not coined until 1906.1 It was just a few years later (in 1910) that Dr. Meltzer linked asthma with allergies.1,3 So, for the rest of the century, asthma was often referred to as an allergic disorder.
In 1987 Th2 cells were discovered and linked to asthma and allergies.4,5 Th2 cells were soon determined to be the dominating (driving force) in the asthma and allergy responses.
In other words, when you're exposed to your asthma triggers, an abnormal immune response occurs. When this happens, Th2 cells are called into action. They release chemicals (mediators of inflammation) that either directly or indirectly cause airway inflammation. It's this inflammation that causes your allergy and asthma symptoms.
Researchers started referring to this as Th2 dominant inflammation, Th2 associated asthma, or Th2 dominant asthma. So, I prefer go with Th2 dominant asthma.
What is Th2 Dominant Asthma?
It's an asthma subgroup. Many subgroups are defined in the clinical setting. Allergic asthma is a good example here. You are diagnosed with asthma. You are diagnosed with allergies. So, your doctor diagnoses you with the subgroup "allergic asthma."
Th2 dominant asthma is a subgroup defined in the lab. Blood is drawn from you. Chemicals released from Th2 cells will be in your blood if you have it. So, that's how you are diagnosed with Th2 dominant asthma.
Th2 cells are the driving force behind your asthma. Asthma begins with an abnormal immune response. For example, you are exposed to dust mites. An abnormal immune response occurs.
Th2 cells release chemicals called mediators of inflammation, or Th2 mediators. Common Th2 mediators that cause asthma are interleukin 4 (IL4), Interleukin 5 (IL5), and Interleukin 13 (IL13). I defined how these affect asthma in my post, "Late Phase Asthma Attack." These mediators cause a special type of airway inflammation called "Eosnophilic Inflammation." This is what causes your asthma symptoms.
So, your blood is drawn. If you have lots of these mediators, you are diagnosed with Th2 Dominant Asthma. This subgroup is often referred to as an umbrella term. This means that many other asthma subgroups fall under it. I will list some of these other subgroups in a moment. But first, let's get rid of an old asthma myth.
Is all Th2 Dominant Asthma allergic?
After Meltzer linked asthma and allergies, researchers thought all asthma was allergic. After 1987, they thought all asthma was Th2 Dominant. However, since 1987, they have learned that this is not true. They now know that only about 50% of asthma cases are Th2 Dominant.
The other 50% of asthma cases are dominated by something else. This other 50% is often lumped under a new asthma subgroup called Non-Th2 dominant asthma.1
Today, researchers know many subgroups fall under the Th2 dominant asthma umbrella. However, keep in mind that not all of these subgroups are allergic. You can have Th2 dominant asthma and not have allergic asthma. So, that's kind of a neat new fact. This shows that the Th2 dominant response is much more complex than once thought.6
What subgroups fall under the Th2 Dominant umbrella?
Their airways are hypersensitive to allergens. It usually has an early onset and therefore is most commonly diagnosed in children. It can be mild, moderate, or severe. This is the most common asthma subgroup. It involves sensitization. It involves the early and late phases of an asthma attack. At the present time, this remains the most understood asthma subgroup.
Their airways are hyper-responsive to exercise. One theory is that rapid inhalation of dry air irritates mast cells lining airways. These mast cells then release Th2 mediators that cause airway inflammation. This is most likely diagnosed in childhood and tends to be mild or moderate. This is also a well-understood subgroup.
Their airways are hyper-responsive, although it’s generally non-allergenic and without the sensitization. It generally has a late-onset (after the age of 12). So, it's usually diagnosed in adults. It is most likely severe asthma. It also presents with chronic sinusitis and nasal polyps.
Their airways are hypersensitive to non-steroidal anti-inflammatory drugs, including Aspirin, Tylenol, and ibuprofen. Their asthma tends to be non-allergic and without the sensitization. It’s usually late-onset and is most likely diagnosed in adulthood. It is usually severe. It is commonly combined with eosinophilic asthma.
Allergic bronchopulmonary aspergillosis
Their airways are hypersensitive to a fungus called Aspergillus fumigatus. It is commonly combined with a sensitivity to allergens, resulting in allergies, sinusitis, eczema, and rhinitis. It may progress to severe asthma and bronchiectasis if not diagnosed early and treated aggressively.
Churg Strauss syndrome
This is severe asthma combined with vasculitis of vessels leading to certain organs, including the lungs, skin, nervous system, gastrointestinal tract, heart, and kidneys. It is associated with rhinitis, sinusitis, neuropathy, rashes, and other symptoms. It progresses and has a grim prognosis if not diagnosed early and treated aggressively.
What's the takeaway?
Th2 dominant asthma is a new asthma subgroup. It's a very specific subgroup diagnosed by having your blood drawn. Once a diagnosis is made your doctor can perform further tests to determine what type of Th2 dominant asthma you have. From there, your doctor can work with you to find what treatment options work best for you. This is all in an effort to help all asthmatics obtain ideal asthma control.
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