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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 also a subgroup. But, it’s 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 I will delve further into Non-Th2 Dominant Asthma in a future post. (So, stay tuned!)

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?

Allergic

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.

Exercise Induced

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.

Eosinophilic

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.

Aspirin Exacerbated

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.

This article represents the opinions, thoughts, and experiences of the author; none of this content has been paid for by any advertiser. The Asthma.net team does not recommend or endorse any products or treatments discussed herein. Learn more about how we maintain editorial integrity here.

  1. Wenzel, Sally, “Asthma Phenotypes: The evolution from clinical to molecular approaches,” Focus On Asthma, 2012, http://www.healthylungs.com.au/resources/WenzelAstham-Phenotypes.pdf, accessed 3/1/19
  2. Mittman, Gregg, "Breathing Space," 2007, New Haven, London, Yale University Press, page 53
  3. Lipkowitz, Myron A., Tova Navarra, "Encyclopedia of Allergies," 2nd edition, 2001, New York, page 173
  4. Jackson, Mark, "Asthma: A Biograhy," 2009, New York, Oxford University Press, page 115
  5. Soderberg, Margaret L, "The Mast Cell Activation Syndrome: A Mini Review," Immunology, 2015, https://medcraveonline.com/MOJI/MOJI-02-00032, accessed 3/1/19
  6. Zhu, Jinfang, William E. Paul, "CD4 T-Cells: fates, functions, and faults," Blood, 2008, September 1, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2518872/, accessed 3/1/19

Comments

  • AnnM.
    2 months ago

    Fascinating article! This should be a must read for insurance companies and er docs. I have asthma and dust mite allergies; it was a sharp er doc who figured out the dust mite issue. I take different meds to control each of them; sometimes getting approval from insurance companies is a challenge.

  • John Bottrell, RRT moderator author
    2 months ago

    Hi. AnnM. Glad you enjoyed the article. I think it would be neat if insurance/pharmacy/doctors hung out in communities like this and read articles like this. That would certainly be a boon for both them and for us. Thanks. John. Site Moderator.

  • Sumra Alvi moderator
    2 months ago

    Hi Ann!So glad you found this article to be relatable. You make a great point about insurance companies and ER docs. This would be a great read for them and it’s definitely a challenge to get approval from them when they are often ill informed about allergies/asthma. Thanks for your comment, hope to hear more from you! Best,Sumra (Asthma.net Team)

  • Shellzoo
    3 months ago

    I have been told I have allergic asthma but, I know I wheeze when I exercise and I have lots of nasal/sinus issues, eczema, can’t take aspirin products…. I wonder how many of us crossover into other subgroups. Whatever the subgroup is, I for one am glad my asthma seems to be well controlled and responding well to Symbicort and Spiriva. Whatever the subgroup, getting asthma controlled well is most important. Great article!

  • John Bottrell, RRT moderator author
    3 months ago

    Thank you. And I agree. The most important aspect is to obtain the best possible control you can. And I think, when it’s all said and done, each subgroup will have it’s own guidelines, and maybe even will break off into diseases of their own with their own treatments. And they will all probably be diagnosed by a blood test. And I certainly think most of us asthmatics probably have more than one subgroup of asthma. I don’t doubt that for a second. It’s interesting to think about. John. Author/ Site Moderator.

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