A Primer on Th1, Th2 in Asthma

Last updated: May 2018

You may have heard a lot about inflammation and cytokines, etc and their importance in asthma. Researchers have made many strides in understanding Th2 (Type 2) inflammation and the important role it plays in asthma, however there is much to still understand. Of particular interest is the role of Th1 inflammation and its correlation to asthma that is more difficult to control.

So what exactly are Th1 and Th2 in asthma?

Let's start with the essential components, the cells! I will try not to bore you or make you get out those first year university textbooks. I have found that when my doctor talks about these things, I need to break them down to understand what he is talking about. It does help that he usually draws diagrams. Okay, I will confess sometimes decoding the diagrams are a feat onto themselves. I suppose it is better than not receiving the information.

First things first, let's start with the cytokines which are hot item as asthma research moves more towards precision medicine.

What are Cytokines?

Cytokines are hormonal messengers that are responsible for cell mediated immunity and allergic type responses.1 There are two main groups, ones that are  pro inflammatory  (promote inflammation), and those that are anti-inflammatory (reduce inflammation). Next up, is the very important T Lymphocytes, these are a major source of cytokines, they have antigen specific receptors on their cellular surface that allows them to recognize normal tissue during episodes of autoimmune disease. There are two kinds of T-Lymphocytes are CD4 and CD8. T Lymphocytes that express CD4 are helper T cells. They are most prolific cytokines producers. You may remember the helper T cell from your high school biology class. I pretty sure that my biology teacher had a rhyming song for helper T cells. This group of cytokines can be further sub divided into the Th1 type cytokines and Th2 type cytokines.

Th1 and Th2 Cytokines

Th1 produces pro inflammatory responses, they are responsible for killing intracellular parasites and disturbing autoimmune responses.1 Interferon gamma is the main Th1 cytokine. It is important to highlight that excessive pro inflammatory responses can lead to uncontrolled tissue damage. Researchers are working on mechanisms to treat this type of inflammation.

Th2 inflammation includes interleukins 4, 5, 13 and are associated with the promotion of IgE and eosinophilic responses in atrophy and IL-10 which has more of an anti-inflammatory response.1 When there is an abundance of Th2 it will counteract Th1 mediated responses. Researchers have found that an optimal balance of Th1 and Th2 production is thought to be best for immune challenges. You may be familiar with these interleukins from the biologics for asthma that have recently come to market. Many specifically target the highlighted interleukins.

Researchers suspect that allergy is a Th1 weighted imbalance and researchers are working on ways to redirect allergic Th2 responses in favor Th1 responses to try and reduce occurrences of atopy.

Ongoing research is investigating ways to prevent incidences of asthma by studying pregnancy and early post nasal life. While research is moving in this direction, it is in its infancy but the future is bright.

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