I have written about how viruses trigger asthma, about virus-induced asthma, and I explained how viruses impact asthma. Here, I thought I’d explore the “biological processes” that occur when you’re exposed to a virus, those processes that link a virus to cold symptoms and eventually to asthma.
I know! I know! I promised I wouldn’t go this deep. However, I changed my mind when I decided this would be a neat way of introducing you to the mediators of inflammation — if you haven’t met them already. I understand I’m using some big, scientific words that might scare some of you away, but don’t worry: I will keep this simple for your sake and my own.
So, what are the mediators of inflammation?
They are tiny proteins that are released from cells when you’re exposed to pathogens like respiratory viruses. They communicate with other cells, telling them that a pathogen — in this case a virus — is present. They tell cells what to do. They either directly or indirectly “mediate” inflammation. In our case, they impact cells of our upper airway, such as inside your nose or throat.
How do mediators cause inflammation?
Some go directly to cells — in our case, airway epithelial cells in your nose — and cause them to release some of their fluid to the interstitial spaces (spaces between tissues). This causes redness and swelling, or inflammation, inside your nose, sinuses, and throat.
Why do they cause inflammation? This might sound bad, but it’s good. It’s your body’s natural way of trapping viruses. This inflammation irritates goblet cells that are randomly scattered along your airway, and this increases mucus production. The mucus is needed to ball up viruses and move them to the back of your throat to swallow them. They are then dissolved by acidic stomach juices.
What is the downside to all this?
Unfortunately, while the mediators are helpful in getting rid of viruses, this inflammation irritates nerve endings lining your airways causing that funny feeling in your nose and throat. Because it also irritates goblet cells, you may develop a runny nose, nasal drainage, or a stuffy nose as a result. These are your prototypical cold symptoms.
What are granulocytes?
Before we move on, I need to give you one more definition. Granulocytes are white blood cells (leukocytes) that contain granules. Among the granules are some mediators of inflammation. The most common granulocytes are mast cells that line airways, and eosinophils and neutrophils. Once recruited to airways, they release even more mediators of inflammation. The purpose of this is to enhance the inflammatory effect to get rid of the virus once and for all.
What are some mediators responsible for cold symptoms?
I’m just going to list a few here. These are released by cells infected by viruses. They either go directly to airway cells to directly cause inflammation, or they travel through the bloodstream to recruit eosinophils and Neutrophils).
- Interleukin 8 (IL8). It travels through the bloodstream and recruits neutrophils. Once inside the airway, neutrophils release their contents, which include even more mediators of inflammation, including more IL6 and IL8. This kind of creates on an ongoing cycle that results in more persistent or severe inflammation. As I explain in my post “Neutrophilic Asthma,” they are also responsible for more persistent and severe asthma3,4.
- Leukotriene B4 (LTB4). They also travel through the bloodstream to recruit neutrophils3,4.
- Interleukin 6 (IL6). They travel through the bloodstream to enhance the production of neutrophils3,4.
- Interleukin 11 (IL11). It travels through the bloodstream and recruits eosinophils. Once inside the airway, they release their contents, which include more mediators of inflammation. Their job is also to enhance the inflammatory response.
- RANTES (CCL5). It also travels through the bloodstream to recruit eosinophils3,4.
Can these mediators cause new-onset asthma or trigger asthma?
Scientists believe the answer here is yes. It’s also important to understand that these same mediators can travel to the lower airways to cause lower airway inflammation or make inflammation already present worse. This can lead to new-onset asthma. It can also cause asthma attacks, even in those considered to have controlled asthma.
What are biological pathways?
We all have genes. Each gene is responsible for making a protein, and each protein tells a cell to do something. Some genes are responsible for proteins that moderate the immune system. Some of these genes make proteins responsible for the mediators of inflammation. For example, Gene IL8 makes the mediator IL8. When you are exposed to viruses, IL8 is released, and this begins the immune response necessary for getting you healthy.
Unfortunately, the biological pathways responsible for getting pathogens like viruses out of your body are also responsible for cold symptoms. And, as you can see here, they may also be responsible for asthma. There are much more mediators of inflammation, some of which are responsible for allergies and asthma. I will introduce you to some in an upcoming post. So, stay tuned!