Haiyaa, why no peanuts? Why so weak?

An iconic line by Malaysia’s own Uncle Roger whenever someone rejects peanuts due to allergies. Most of us will know that an allergy is not to be taken lightly due to the risks it carries. However, have you ever stopped to wonder, why though? How can something as harmless as peanuts cause someone to go into life-threatening situations? Especially in the current season of spring, it might be blasphemous to even ponder upon the fact that pollen can cause ICU admissions. Fret not, this article will introduce you guys to the physiology behind allergies, and how our immune system can really mess stuff up.

Why are we discussing this topic?

First and foremost, what is an allergy and why is it important? In brief, an allergy is an exaggerated immune response to certain foreign substances that can lead to a wide range of side effects, ranging for mild irritation to anaphylaxis, a potentially life threatening condition that includes nausea, difficulty breathing, vomiting, extremely low blood pressure, and if untreated death (Mayo Clinic, 2018). Contrary to popular belief, allergies affect adults and children alike, with the CDC reporting more than one quarter of adults and 1 in 5 children having seasonal allergies, as well as 6% of adults and children having food allergies (CDC, 2023).

Figure 1: CDC Statistics for Allergies

Fun stuff

With that out of the way, let’s dive into the intricacies of what makes an allergy so dangerous. Our immune system is normally there to help keep us safe from harmful substances such as bacteria, viruses, and other microorganisms. The immune system is composed of many different cell types such as macrophages, lymphocytes, mast cells, and many more. Usually, when these cells detect something foreign in the body, they secrete specific substances to initiate inflammation and to prevent the pathogens from harming the body. Allergic reactions begin in the immune system when harmless substances such as dust, pollen, or food substances are recognized by these cells and trigger an immune response (John Hopkins Medicine, 2019).

There are many different types of allergies, but the most common ones are IgE-mediated, which is what we will discuss mostly here (Dougherty, Alsayouri and Sadowski, 2020). During the first exposure to an allergen, dendritic cells and macrophages gobble up the allergen and present them to a T-helper cell. The T-helper cells then scours the body to present this allergen to B-cells that have a specific receptor for the allergen. Once this match has been found, the B-cells rapidly multiply and produce IgE antibodies specific to the allergen. These antibodies bind onto mast cells and basophils, which are another type of immune cells. This phase is usually called the sensitization phase (Charles A Janeway et al., 2001). 

Figure 2: Development of immunological memory to allergens. Image taken from FutureLearn.

During the next exposure, these allergens bind to the IgE antibodies and cause the mast cells and basophils to degranulate and release the contents in it. The contents include histamine, and prostaglandins which cause systemic inflammation. Normally, these molecules help dilate blood vessels, and recruit immune cells to the rescue. However, during allergic reactions, the release of these molecules is excessive and causes too much vasodilation, which can result in low blood pressure. Besides, it can also cause excessive mucus secretion, stimulation of sensory nerves, and smooth muscle spasms. This can cause someone to enter a state of anaphylactic shock, with symptoms such as hypotension, difficulty breathing, dizziness, nausea, an abnormal heart rate, and loss of consciousness  (Dougherty, Alsayouri and Sadowski, 2020).