An estimated 20% of Australians have an allergic disease, with Melbourne as a hotspot where one in three people experience hay fever and thunderstorm asthma. Allergies can affect the skin, sinuses, airways, gastrointestinal tract, or other organs.
Allergies are immune reactions to foreign antigens, causing tissue inflammation and organ dysfunction. Symptoms depend on prior immune response, antigen exposure, and genetic factors. Atopic individuals have a genetic predisposition to conditions like allergic rhinitis, atopic dermatitis, allergic asthma, and IgE-mediated food allergies. Reactions can be immediate (within 60 minutes) or delayed (hours, days, or weeks).
In 1963, Gell and Coombs classified hypersensitivity reactions into four types based on the immune response.
Type 1: Immediate hypersensitivity: IgE antibodies on mast cells bind to antigens, causing cell degranulation. This leads to vasodilation, smooth muscle contraction, mucous secretion, and inflammation. Anaphylaxis is a severe form needing adrenaline intervention. Food allergies affect 4-7% of children, often involving milk, eggs, peanuts, tree nuts, shellfish, wheat, and soy.
Type 2: Antibody-mediated hypersensitivity: IgG or IgM antibodies, with complement or phagocytic cells, cause reactions seen in blood transfusions, rheumatic fever, and autoimmune diseases.
Type 3: Immune complex-mediated hypersensitivity: Antigen-antibody complexes cause inflammation, as seen in chronic glomerulonephritis, SLE, and rheumatoid arthritis.
Type 4: Delayed hypersensitivity: T cells and persistent antigens trigger cytokine secretion and monocyte activation. This occurs in conditions like tuberculosis and leprosy, with reactions peaking 48-72 hours after exposure.
In this podcast, we explore the prevalence of allergies, their signs and symptoms, and common diagnostic tests. We also discuss non-allergic sensitivities like reactions to nitrates, sulphites, and food additives.
Dr Colin Little, a Melbourne-based immunologist and allergist with over 40 years of experience, provides insights on treating common and rare allergic conditions.
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
