Episode 149. Allergy and Food Sensitivity with Dr Colin Little

It is estimated that 20 % of the Australian population has an allergic disease with Melbourne often cited at the epicenter where at least one in three people experience hay fever and thunderstorm asthma is a frequent news headline. Allergies may present in many different ways manifest in the skin, the sinuses and airways, the gastrointestinal tract or within virtually any organ. 

Allergy is an immunologically mediated hypersensitivity reaction to a foreign antigen and is manifested by tissue inflammation and organ dysfunction. The clinical expression of allergic disease depends on prior immunologic responsiveness, antigen exposure and genetic factors specific to the host. Atopic patients have a genetically aggregated predisposition to a variety of disorders including allergic rhinitis, atopic dermatitis, allergic asthma and IgE -mediated food allergies. Reaction may be immediate (occurring within 60 minutes of exposure) or delayed (hours, days, or weeks after antigen exposure) reflecting different pathogenetic processes.

In 1963 Gell and Coombs introduced a systematic classification of the different types of hypersensitivity reactions involving the adaptive immune system naming Types 1 to 4 based on the types of antigens and immune responses involved.

In type 1; Immediate hypersensitivity, IgE antibodies occupying receptor sites on mast cells become linked to multivalent antigens activating and degranulating the cell. Clinical effects may be immediate and are explained by the actions of released mediators on target end organs which may include vasodilation and permeability changes, smooth muscle contraction, mucous secretory gland stimulation and tissue inflammation. 

Anaphylaxis is the most serious example of mast cell and basophil mediator release requiring immediate pharmacologic intervention with adrenaline which boosts intracellular CAMP inhibiting mast cell degranulation. Type 1 reactions explain food allergy, observed in at least 4-7 % of children with some studies suggesting a much higher percentage.

Food allergy is generally caused by proteins found in milk, eggs, peanuts, tree nuts, shellfish, wheat and soy. Milk and egg allergies in atopic children are often outgrown by adulthood.

Interestingly individuals with seasonal pollen allergies may experience itching of the oral mucosa upon ingestion of some raw fruits and vegetables. Alpha-gal is a carbohydrate found in red mammalian meats such as beef, pork and lamb (not human muscle) with sensitisation linked to tick bites.

Type 2 hypersensitivity is antibody mediated by IgG or IgM together with complement or phagocytic cells and may be observed in blood transfusion reactions, rheumatic fever and many autoimmune diseases. 

Type 3 hypersensitivity is antigen-antibody complex mediated with inflammation involving complement and polymorphs reacting to immune complex deposition-such as on the endothelium of blood vessels. This reaction is observed in chronic glomerulonephritis, SLE and Rheumatoid arthritis.

In delayed or Type 4 hypersensitivity contact between circulating T cells and persisting antigens leads to cytokine secretion with attraction and activation of monocytes and other myeloid cells. This reaction is typically observed in the case of persistent antigens such as with tuberculosis and leprosy and is observed more than 12 hours after exposure to the allergen with a maximal reaction time between 48 and 72 hours.

In this podcast I was curious to explore how common allergic phenomena are in our society, the signs and symptoms to be alert to and the utility of common tests required for work up. I was also keen to question non-allergic sensitivities such as nitrates, sulphites and food additives often implicated in a confusing plethora of symptoms some patients present clinicians with.

Dr Colin Little is a physician specialised in immunology and allergy. He has been treating patients in Melbourne’s busy metropolitan regions for over 40 years and is credited with thinking outside the box and assisting a great many patients with their common and exotic allergic and immune phenomena.

References :

Dr Colin Little: 1/324 Stephensons Rd Mt Waverley 3149

Hypersensitivity-an overview. Science Direct 

Immediate Hypersensitivity Reactions.AAJ Vaillant.2022. ⁠www.ncbi.nlm.nih.gov⁠

Hypersensitivity Reactions, April 2009. Rutgers New Jersey Medical School