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Tag: extrinsic asthma

Dear Dr. K –

Dear Dr. K –

My husband has intrinsic asthma and I have extrinsic asthma.  Despite having our COVID vaccines he caught COVID and I didn’t.  What’s up?

Well, first of all I’m impressed that you know the difference between intrinsic and extrinsic asthma phenotypes.  To try and simplify what is a complex science most asthma can be categorized as high TH2 (extrinsic) or low TH2 (intrinsic).  TH2 is a type of lymphocyte that can cause inflammation.  In high TH2 asthma the main mediators of inflammation are IL4, IL5, and IL13.  IL means “interleukin” a chemical that communicates to cells (cytokine).  In low TH2 the main cytokines are IL-1B, IL17, IL8, and IL6.  The inflammatory cells that cause the mischief are eosinophils (in high TH2) and neutrophils (in low TH2). 

OK, I know that was a lot to throw at you but it is extremely relevant.  It’s not just you and your husband that have had different outcomes but asthmatics worldwide.  As it turns out extrinsic (allergic) asthma (high TH2) causes high levels of IL13.  IL13 seems to have three protective effects for corona virus infection.  First of all, IL-13 increases the density of the cilia lining our airway cells.  These microscopic hairs are a natural clearance mechanism to sweep microbes out of our bodies.  IL-13 also dials back production of a surface protein ACE2 which is the portal of entry for corona virus to cause infection.  Finally, IL-13 ramps up production of a protective carbohydrate called keratin sulfate.  Think “Teflon coating”.  The keratin provides a physical barrier to the corona virus.  You produce extra IL-13 and your husband doesn’t.  Hence the different outcome.