What's the Relationship Between Allergies, Immunity, and Cancer?
According to statistics released by the World Allergy Organization (WAO), the incidence of allergic diseases has increased at least threefold over the past 30 years, with the global prevalence of allergies now reaching 22%. This has led to various rumors, including the notion that allergies indicate an overactive immune system, and some even claim that people with allergic constitutions have stronger anti-cancer abilities.
But are these claims true? What is the actual relationship among allergies, immunity, and cancer? And how are anti-allergy treatments related to anti-tumor therapies? On the occasion of World Allergy Week, let’s explore these questions.
Allergy is a phenomenon in which the body exhibits an abnormally heightened sensitivity to specific external substances, commonly referred to as allergens [1]. Antibodies are proteins produced by the immune system in response to allergens, and they function to recognize, mark, and neutralize antigens. Common antibodies include IgE, IgG, IgM, and IgA.
In daily life, allergies usually occur as follows:
when an external allergen enters the body, it stimulates the immune system to produce immunoglobulin E antibodies (IgE), a process known as sensitization. When the allergen binds to these antibodies, the immune system immediately recruits a “task force” to respond. The key members of this task force are mast cells and basophils, which release substances that cause various allergic symptoms—ranging from mild rashes and sneezing to severe, life-threatening reactions [2].
Some individuals naturally have immune systems that produce IgE more easily than others; these are often described as having an “allergic constitution.”
It can be concluded that the occurrence of allergic reactions is not related to the overall strength of the immune system but rather to the presence of allergens. In other words, allergies reflect a dysregulated immune response. A healthy immune system is balanced, neither too weak (failing to recognize non-self) nor too hyperactive (attacking normal cells).
Common allergens in daily life:
Inhaled allergens: pollen, dust mites, animal dander, automobile exhaust, cigarette smoke, etc.
Ingested allergens: milk, eggs, fish, shellfish, beef, lamb, nuts, etc.
Contact allergens: UV rays, cosmetics, hair dyes, synthetic fabrics, metal jewelry (watches, necklaces, rings, earrings), bacteria, viruses, etc.
Injected allergens: penicillin, streptomycin, heterologous serum, etc.
As mentioned above, the immune system can “recognize non-self” elements in the body. Therefore, many people assume that a very strong immune system can detect and eliminate cancer cells. However, current global research suggests that when it comes to cancer and immunity, the key question is not simply whether the immune system is “strong or weak” but whether it can correctly recognize cancer cells.
Normally, when the body’s cells are infected by viruses or bacteria, danger signals trigger immune responses. Cancer cells, however, originate from normal cells and are very cunning; they often “disguise” themselves as healthy cells, evading immune detection. Even when recognized, cancer cells may release substances that “confuse” or “escape” the immune system, preventing it from attacking them [3].
Thus, the ability of the immune system to fight cancer is limited.
The relationship between allergic reactions and tumors has long been unclear and debated.
However, a study published in Cancer Cell in November 2021, titled “The allergy mediator histamine confers immunotherapy resistance in cancer patients via activation of the macrophage histamine receptor 1” [5], revealed a molecular mechanism by which the allergy mediator histamine induces resistance to immunotherapy in cancer patients via activation of histamine receptor 1 (HRH1) on macrophages. The study found that antihistamine treatment, a commonly used anti-allergy therapy, can enhance responses to immune checkpoint inhibitors, particularly in patients with high histamine levels in the blood.
This discovery provides evidence for a potential connection between allergic reactions and malignant tumors (especially tumor immunology) and offers experimental guidance for clinical drug choices in cancer patients experiencing allergies during immunotherapy.
That said, allergic diseases and malignant tumors are both complex conditions, and this study only scratches the surface of their possible relationship. Further multi-dimensional and in-depth research is needed. Nevertheless, for cancer patients, such research points to more therapeutic possibilities and potential avenues for cure—something to look forward to.
References:
[1] Medical Immunology (7th edition), People’s Medical Publishing House
[2] Maksymilian Chruszcz, Brenda Kapingidza, Dolamore Coleman, Krzysztof Kowal. A Robust Method For The Estimation And Visualization Of IgE Cross-Reactivity Likelihood Between Allergens Belonging To The Same Protein Family. PLoS ONE, 2018;13(11):e0208276.
[3] Cancer Update Email – It’s a Hoax! Retrieved Dec 4, 2020, from https://www.hopkinsmedicine.org/kimmel_cancer_center/news_events/featured/cancer_update_email_it_is_a_hoax.html
[4] Newnes HV, Armitage JD, Audsley KM, Bosco A, Waithman J. Directing the Future Breakthroughs in Immunotherapy: The Importance of a Holistic Approach to the Tumour Microenvironment. Cancers (Basel), 2021;13(23):5911.
[5] Li H, Xiao Y, Li Q, et al. The Allergy Mediator Histamine Confers Resistance to Immunotherapy in Cancer Patients via Activation of the Macrophage Histamine Receptor H1. Cancer Cell, 2021;S1535-6108(21)00602-4.
