Pathophysiology Immune Disorders Question

Question

1. A 32-year old man presents in the allergy clinic with complaints of allergic rhinitis or hay fever. His major complaints are those of nasal pruritis (itching) nasal congestion with profuse watery drainage, sneezing and eye irritation. The physical examination reveals edematous and inflamed nasal mucosa and redness of the ocular conjunctiva. He relates that this happens every fall during “ragweed season.”  
2. Explain the immunologic mechanisms that are responsible for this man’s symptoms.  
3. What type of diagnostic test might be used? 

Answer 1

Sounds like he is having an allergic reaction to pollen.

a. An allergic reaction is a type 1 hypersensitivity reaction. Mechanism -->

1. Sensitization stage: First exposure to allergen causes Th0 cells to produce IL-4, which drives Th0 cell differentiation to Th2 cells. Th2 cells secrete more IL-4 which causes B lymphocytes to isotype switch to IgE. IgE can then bind to the Fc receptor on mast cells.
2. Re-exposure: Second exposure to allergen will allow the allergen to cross-link several IgE molecules already bound to mast cells (due to the first exposure). Cross-linking of the IgE causes mast cell degranulation, releasing 1^o and 2^o mediators.
3. 1^o mediators: Histamine (vascular leakage --> edema), heparin (anticoagulant), and chemotactic factors (recruits more cells)
4. 2^o mediators: Prostaglandins/leukotrienes (increased vascular permeability and smooth muscle contraction), leukotriene B₄ (neutrophil recruitment). These mediators are produced during the reaction for the purposes of increased potency and increased duration of the reaction.

b. Two types of tests can be used - Skin test and a blood test

1. A skin test is the most common type of test for diagnosis. Your skin is labeled and then pricked with a various number of different allergens (allowing the allergen to get under the skin). If allergic to any of the substances your skin will become red, itchy, and irritated roughly 30min after the exposure.
2. A blood test is used if the skin test is contraindicated, such as if a medicine you are taking can interfere with the results, have a skin condition, or have a severe reaction during the skin test. The ELISA (enzyme-linked immunosorbent assay) is an extremely sensitive test used to detect the presence of allergen-specific IgE antibodies in the blood.