Throat Allergy - Types of Hypersensitivity Reactions

The Four Types (Gell & Coombs Classification)

Type I - Immediate Hypersensitivity (Most Common "Throat Allergy")

• Mediator: IgE antibodies
• Mechanism: On first allergen exposure, Th2 cells drive B cells to produce IgE, which coats mast cells. On re-exposure, the allergen cross-links IgE on mast cells, causing degranulation and release of histamine, leukotrienes, and prostaglandins.
• Throat symptoms: Throat tightness, itching/pruritus of the throat, angioedema of the pharynx/larynx, swelling
• Onset: Within minutes (< 1 hour)
• Common triggers: Pollen (trees: Feb-May; grasses: Apr-Aug; weeds: Jul-frost), animal dander, molds (inhalants), foods, drugs, insect venom
• Associated conditions: Allergic rhinitis with post-nasal drip irritating the throat, asthma, angioedema, anaphylaxis
• Most severe form: Laryngeal angioedema in anaphylaxis - can be life-threatening

Type II - Cytotoxic Reaction

• Mediator: IgG and IgM antibodies bind to cell-surface antigens
• Mechanism: Antibody-antigen complexes on cell surfaces activate complement (C3b) and recruit macrophages/NK cells, leading to cell destruction
• Throat relevance: Rare direct throat involvement. Seen with certain drug reactions affecting mucous membranes (e.g., pemphigus affecting oral/pharyngeal mucosa), transfusion reactions
• Examples: Hemolytic anemia, thrombocytopenia, Hashimoto thyroiditis

Type III - Immune Complex-Mediated Reaction

• Mediator: IgG/IgM antibodies form soluble immune complexes with antigens
• Mechanism: Immune complexes deposit in vessel walls, activate complement, recruit neutrophils, causing local inflammation (Arthus reaction) and tissue injury
• Throat relevance: Serum sickness can cause pharyngeal inflammation, arthralgia, and fever. Vasculitis may affect throat mucosa.
• Examples: Serum sickness, SLE, rheumatoid arthritis

Type IV - Cell-Mediated (Delayed) Hypersensitivity

• Mediator: Sensitized T lymphocytes (Th1 cells) - NO antibodies involved
• Mechanism: T cells recognize antigen, recruit more lymphocytes and macrophages to the site; reaction takes 48-72 hours (up to 3 days) to develop
• Throat relevance: Contact reactions to inhaled or ingested chemicals, certain drug reactions (e.g., Stevens-Johnson syndrome involving oral/pharyngeal mucosa)
• Examples: Contact dermatitis, SJS/TEN (affects mucous membranes including throat), DRESS syndrome, PPD test reaction

Summary Table

Allergic Trigger Categories (for Throat Allergy)

1. Inhalants - pollen, animal dander, molds (most common cause of allergic rhinitis/throat symptoms)
2. Ingestants - foods, medications
3. Injectants - drugs, insect venom
4. Contactants - nickel, poison ivy, topical medications

Diagnostic Testing for Throat/Airway Allergy

• Skin prick/puncture test - excellent screening, low false-positive rate
• Intradermal dilutional testing (IDT) - most common method used by otolaryngologists, highly sensitive
• RAST (in vitro) - measures serum allergen-specific IgE; more specific than skin testing

Treatment

• Antihistamines - block histamine H1 receptors (Type I)
• Corticosteroids - reduce inflammation across types
• Epinephrine - first-line for laryngeal angioedema/anaphylaxis
• Immunotherapy (subcutaneous or sublingual) - shifts immune response, increases IgG4, requires 3-5 years; treats the underlying sensitivity