The specialty of allergy and immunology

What is the specialty of allergy and immunology?

The specialty of allergy and immunology focuses on the immuno-inflammatory response and its clinical repercussions. The immuno-inflammatory response serves to protect us from infections and up to a certain point against the development of certain cancers. The immune system is a bit like an "army", always on guard, ready to react as a first line of defence and able to notify other defensive processes even more specialised in case of an even more aggressive attack.

Theoretically, there are two different types of immuno-inflammatory responses:

• The innate inflammatory response when only cells and proteins responsible for an initial inflammatory response are involved: including epithelial cells, phagocytes (neutrophils, macrophages and monocytes, and eosinophils), dendritic cells, mastocytes, natural killer cells (NK) and innate lymphocytes, and complement proteins.
• The adaptive immuno-inflammatory response, when cells responsible for the immune system are activated in order to amplify the inflammatory response (B and T lymphocytes). The adaptive immune system responds in two ways:
• The humoral immune response, medated by the production of antibodies by B lymphocytes (IgM, IgG, IgA et IgE)
• The cellular immune response, mediated by T lymphocytes: there are several different kinds of T lymphocytes

Normal and protective immunity

Once our "army" has succeeded in vanquishing an adversary, it remembers all the details of the aggressor in question, so that if it encounters the same enemy in the future, the reaction will be even faster and more effective. Thanks to vaccines, we are able to "teach" our army about the nature of certain infections, without the actual risk of infection, so that in the future, our "army" is already prepared to respond rapidly and effectively. We then say that we are "immunised".

The immune system can occasionally cause trouble in two main ways: either because it isn't strong enough – and here we speak of immunodeficiency; or because it acts in an inappropriate fashion – here we speak of hypersensitivity.

Immunopathology

Immunodeficiency

Immunodeficiency states can be primary, often related to inherited genetic traits or newly acquired (these are called genetic mutations). There are many different primary immunodeficiency states.

Immunodeficiency may also be acquired:

• due to an infection such as measles, which can lead to a temporary immune deficit, or to infections such as HIV, responsible for a progressive deficit, and up until now, irreversible (although infection can be slowed and stabilized with current treatments)
• due to a systemic illness, such as diabetes or renal (kidney) failure
• due to a dysfunction of certain blood cells, or from treatment with immunosuppressive agents
• cancer of certain blood cells: myelodysplasia, leukemia, or lymphoma
• aplastic anemia

Hypersensitivity

Even during a battle, though, even if the immune system successfully defeats the enemy, there is often collateral damage: that's what we call hypersensitivity. For example, when our immune system defends us against a bacterium, such as tuberculosis, the inflammatory cells don't only destroy the bacteria, they can also injure part of the neighbouring tissue, leaving scar tissue once the battle has finished. Every infection is associated with a certain degree of hypersensitivity.

In certain circumstances the hypersensitivity is not necessarily associated with a defence against an aggressor, or infection. There are two main types of hypersensitivity.

• Innate hypersensitivity, without implying participation of lymphocytes, including autoinflammatory syndromes that are characterised by an excess reaction of the innate immune system, in people who are genetically predisposed.
• Acquired hypersensitivity, implying the participation of lymphocytes. Dr. Bellanti (see below), breaks this into 3 main sections:
• allergy, when the allergen is a molecule that is foreign to human beings, such as pollen, animal allergens, cosmetics or medications
• graft rejection, when the antigen is human in origin, such as a kidney, liver, heart or lung
• autoimmunity, when the antigen belongs to one's own self: autoimmunity directed against an organ (type 1 diabetes, autoimmune thyroiditis, autoimmune thrombocytopenia etc.) or in a more generalised form (lupus, scleroderma, rheumatoid arthritis, etc.).

Who are the specialists in allergy and immunology?

The specialist in Allergy and Immunology is a physician who after his or her medical studies has completed 5 years of specialty training: 3 years of internal medicine or pediatrics, followed by at least 2 years in allergy and immunology.

Références:

Bellanti JA. Immunologically mediated diseases. Dans: Bellanti JA. Immunology III,Saunders 1985:346-446.

Properties and overview of immune responses. Dans: Abbas AK, Lichtman AH, Pillai S. Cellular and molecular immunology,10è éd,Elsevier 2022:1-11.

Jutel M, Agache I, et al. Nomenclature of allergic diseases and hypersensitivity reactions: adapted to modern needs: an EAACI position paper. Allergy 2023;78:2851-2874.

Krainer J, Siebenhandl S, Weinhäusel A. Systemic autoinflammatory diseases. Journal of Autoimmunity 2020;109:1-10.

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André Caron, MD FRCPC
(translation: Andrew Moore, MD FRCPC)

Mise-à-jour 09/2024