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“How Can I Have an Allergy If I Have a Weak Immune System?”

Understanding Allergies and Primary Immunodeficiency

By Joshua D. Milner, MD
National Institute of Allergy and Infectious Diseases, National Institutes of Health

Having allergies when you also have a primary immunodeficiency can make anyone’s head spin (or sneeze). Allergies are tricky enough as it is, with different definitions of what an allergy is, to different types of allergies, triggers and responses. But allergies in folks with primary immunodeficiency diseases (PI) present a series of unique challenges. A question we often get is, “How can I have an allergy if I have a weak immune system?” The answer is that in almost every case, having a PI makes only part of the immune system weak. And besides fighting infection, a typical immune system also needs to know how to stop fighting that infection, and to figure out when it isn’t an infection at all. So if one part of the immune system isn’t working well at fighting an infection, it also might not work well in preventing another part of the immune system from going rogue.

There are a number of other reasons allergies occur often in PI. One is that the types of infections, or even the type of resident bacteria and viruses in the gut and skin, can increase one’s risk for allergy. Another is that people with PI often have to take life-saving medicines such as antibiotics, and often intravenously (IV). Increased exposure to medications, especially by IV, no matter who you are, increases one’s risk for allergies to those medications.

Finally, there are quite a few allergies directly caused by certain genetic mutations that cause PI to begin with. In some cases we really don’t know why, such as the increased risk for eczema and food allergies in Wiskott-Aldrich Syndrome, having really high IgE—the antibody that causes allergies—in the Autosomal Dominant Hyper-IgE syndrome due to STAT3 mutations, or the raft of allergies you can get with DOCK8 deficiency. In other cases we do know why, such as PLAID (PLCG2 associated antibody deficiency and immune dysregulation) where a mutation in PLCG2 actually leads the protein to turn on only in the cold. When that happens in mast cells—the cell that produces histamine in an allergic reaction—it causes something called “cold urticaria,” or hives to the cold.

One of the challenges is knowing when it’s an allergy. When you get frequent sinus infections, are they really just caused by the bug or could symptoms be due to an allergy to, say, dust mites? Or is it both? The swelling that allergies can cause in the sinuses makes it easier for bugs to grow there and harder to drain them. Other folks can get diagnosed with recurrent pneumonias, when in fact they are asthma attacks in the context of a cold with fever, which can even look like pneumonia on an X-ray.

To approach these issues, a great start is to have an open mind to the possibility that allergies might be contributing to a problem and get evaluated by an expert allergist/immunologist who understands allergies and the immune deficiency. There are skin tests and blood tests which help make the diagnosis, but they are only guides and never should be used on a fishing expedition to look for some magic allergen that is the root of all the problems—that rarely ever happens. It is critical to also be aware that many issues are not at all related to allergies. Distinguishing fact from fiction is always difficult in medicine, and allergies in the context of PI might be one of the hardest tasks. Getting good reliable information, paying close attention to how your body reacts to many things, and becoming aware of the signs of allergies can help achieve it.

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This article originally appeared in the Spring 2016 edition of the IDF ADVOCATE, the Immune Deficiency Foundation's newsletter. Click here to subscribe.

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