A 10-year-old girl is brought to the office due to sneezing, rhinorrhea, and nasal congestion and itching. The symptoms began 2 days ago after she arrived at a family farm for a summer vacation. The patient has spent a few days visiting the farm during previous summer seasons. She had no symptoms at her first visit 2 years ago but recalls having similar symptoms last year. She has had no respiratory symptoms while residing in another state the rest of the year. The patient has no prior medical conditions and takes no medications. On physical examination, the nasal turbinates are enlarged and bluish; clear rhinorrhea is present. Allergic response to a farm allergen is suspected. Which of the following processes most likely occurred during the first farm visit 2 years ago?

Question

A 10-year-old girl is brought to the office due to sneezing, rhinorrhea, and nasal congestion and itching.  The symptoms began 2 days ago after she arrived at a family farm for a summer vacation.  The patient has spent a few days visiting the farm during previous summer seasons.  She had no symptoms at her first visit 2 years ago but recalls having similar symptoms last year.  She has had no respiratory symptoms while residing in another state the rest of the year.  The patient has no prior medical conditions and takes no medications.  On physical examination, the nasal turbinates are enlarged and bluish; clear rhinorrhea is present.  Allergic response to a farm allergen is suspected.  Which of the following processes most likely occurred during the first farm visit 2 years ago?

Quizplus · Accepted Answer

This patient with allergic rhinitis (eg, location-based sneezing and rhinorrhea; bluish, congested nasal turbinates) likely became sensitized to farm allergens during her first visit. Allergic rhinitis is a form of type 1 hypersensitivity, a process that involves sensitization and elicitation phases. Sensitization occurs when inhaled antigens penetrate the nasal epithelium and are presented on major histocompatibility complex (MHC) class II molecules, causing activation of naive T-helper (Th) cells. The release of cytokines (eg, IL-25, IL-33) from the nasal epithelium causes Th cells to differentiate into Th2 cells that secrete IL-4, IL-13, and other lymphokines that stimulate B cell maturation and production of IgE antibodies. Antigen-specific IgE antibodies then bind to the high-affinity IgE receptor on mast cells, priming the patient for an allergic response. Repeat exposure to the inhaled antigens (eg, on subsequent visits to the farm) cross-links IgE antibodies on the surface of the mast cell, leading to IgE receptor aggregation, which causes mast cell degranulation (Choices A and C). This releases histamine and other vasoactive mediators that lead to nasal inflammation, producing the allergic response. Subsequent exposure to the same antigen can lead to further allergen priming, worsening symptoms over time. (Choice B) Complement activation occurs in type III hypersensitivity reactions, in which immune complexes deposit in the basement membrane of small blood vessels in the skin, kidneys, or joints, resulting in vasculitis. Complement does not play a significant role in type I hypersensitivity. (Choice D) Interferon gamma is secreted by Th1 cells, which activates macrophages and, along with IL-2, stimulates CD8⁺ cytotoxic cells. It inhibits, rather than enhances, the Th2 cell activity that drives type 1 hypersensitivity reactions (eg, allergic rhinitis). Educational objective: Sensitization to aeroallergens occurs when inhaled antigens induce T-helper (Th) cells to differentiate into Th2 cells. Th2 cells then promote B-cell maturation and isotype class switching to IgE.

A 10-Year-Old Girl Is Brought to the Office Due to Sneezing