Types of Hypersensitivity Reactions

Types of Hypersensitivity Reactions

• Type I Hypersensitivity (IgE-mediated): A rapid, allergic reaction triggered by IgE antibodies. It involves mast cell degranulation and release of inflammatory mediators (histamine, prostaglandins, leukotrienes). Symptoms manifest within 15-30 minutes after exposure. Examples include bee stings, latex, and penicillin. Involves skin, eyes, nasopharynx, bronchopulmonary, and gastrointestinal tract.
• Type II Hypersensitivity (Cytotoxic): Mediated by IgG and IgM antibodies, leading to cell destruction. Antigens are often endogenous. Examples include hemolytic reactions, myasthenia gravis (MG) and certain graft rejections.
• Type III Hypersensitivity (Immune Complex): Caused by immune complex deposition, which activates complement proteins and leads to inflammatory reactions. Symptoms may take 3-10 hours to appear. Examples include serum sickness, hypersensitivity pneumonitis, lupus, and some types of vasculitis (e.g., Polyarteritis nodosa).
• Type IV Hypersensitivity (Delayed/Cell-mediated): Involves T lymphocytes, monocytes/macrophages, not antibodies. Examples include contact dermatitis, tuberculin skin testing (PPD), graft rejection, and some autoimmune diseases

Acute Allergic Conjunctivitis

• Causes: Most often Type I hypersensitivity, including seasonal allergies ("hay fever"), food allergies, and atopic conditions.
• Signs: Pinkish conjunctiva (hyperemia), chemosis (swelling), small papillae, potential lid swelling (chronic cases may show dark pigmentation), and a Dennie-Morgan fold (suggestive of atopic dermatitis).
• Symptoms: Severe itching, watery discharge, stringy mucus, possible associated rhinitis, sinusitis, and postnasal drip.
• Treatment: Varies by severity. Mild cases can be managed with cold compresses and over-the-counter (OTC) vasoconstrictors. Moderate to severe cases may require antihistamines, mast cell stabilizers, topical steroids/NSAIDs, and artificial tears/lubricants. Maintenance therapy (1-3 months) involving pre-season treatments may also be beneficial.

Chronic Allergic Conjunctivitis

• Characteristics: Long-standing, recurrent with exacerbations.
• Treatment: Similar to acute treatment but with a focus on maintenance therapy, including artificial tears, cold compresses, mast cell stabilizers, and/or oral antihistamines as needed.

Ocular Anti-allergic Medications

• Antihistamines: H1 blockers (e.g., Naphcon-A, Emadine, etc.). Differences include strength, and a need to be cautious in pre-school children, due to side effects which could appear, if used excessively.
• Mast Cell Stabilizers: Reduce mast cell activity reducing allergic reaction. More effective than antihistamines in this respect. (Cromolyn sodium, Lodoxamide, Nedocromil, Pemirolast). Usually for mild or seasonal acute allergic conjunctivitis and some forms of VKC/GPC.
• Corticosteroids: Example is Loteprednol (Alrex). Used sparingly due to possible side effects including IOP changes. Lower concentrations have anti-inflammatory actions in allergic conditions
• Other combination agents: Many medications available; dual or triple action, which combines antihistamines , mast cell stabilizers and reduce eosinophil chemotaxis (bepotastine, olopatadine, azelastine, epinastine, Alcaftadine)

Adjunctive Systemic Therapy

• Oral Anti-histamines: Benadryl, Chlor-Trimeton (older generation), Allegra, Claritin, Zyrtec are examples. Use caution with angle-closure glaucoma prone patients.
• Steroidal Nasal Sprays: Fluticasone, Budesonide are used for nasal allergy support.

Explore the various types of hypersensitivity reactions in the immune system, including Type I, II, and III reactions. This quiz covers the mechanisms, symptoms, and examples of each type, helping you understand their distinct characteristics and implications in allergy and autoimmune disorders.