Allergic Reactions

Sensitization is the initial process that establishes an allergy. When antigen-presenting cells encounter an allergen, they degrade it into fragments and display these on their surface. These cells activate Type 2 helper T cells, which release signals causing B cells to produce immunoglobulin E (IgE) antibodies. IgE then binds to mast cells, priming the immune system for future allergic reactions to that specific allergen.

When an allergen binds to IgE on mast cell surfaces, it stimulates mast cells to release inflammatory chemicals like histamines and leukotrienes. These mediators cause typical allergic symptoms such as sneezing, runny nose, and nasal inflammation. Additionally, mast cells and helper T cells release signals recruiting other immune cells like eosinophils and basophils, which amplify the inflammatory response.

Antigen-presenting cells (APCs), including dendritic cells and macrophages, initiate sensitization by taking up allergens and degrading them into fragments. APCs display these fragments on their surface and activate Type 2 helper T cells, triggering the humoral immune response that produces IgE antibodies specific to the allergen.

During sensitization, B cells produce IgE antibodies in response to specific allergen fragments presented by antigen-presenting cells. Each IgE molecule is tailored to recognize only its corresponding allergen. This specificity means grass pollen-specific IgE will trigger reactions only to grass pollen, not other allergens, ensuring targeted allergic responses.

Anaphylactic shock is a rapid, systemic allergic reaction that can be life-threatening. Within minutes of allergen exposure, mast cells release large quantities of mediators into the bloodstream, causing airway restriction, blood vessel dilation, increased mucus production, and changes in heart rate. Unlike localized reactions, anaphylaxis affects multiple body systems and requires immediate epinephrine treatment to reverse these physiological changes.

Cross-reactivity occurs when IgE antibodies produced against one allergen trigger an allergic reaction to a different allergen. For example, ragweed pollen-specific IgE might also react to structurally similar allergens. This phenomenon explains why individuals allergic to one substance may experience reactions to seemingly unrelated allergens.

Epinephrine is the only effective medication for anaphylaxis. It counteracts the complex physiological changes by constricting blood vessels, increasing heart rate, stabilizing heart contractility, and increasing airflow through the airways. Rapid administration via EpiPen is critical, as quick response within minutes of allergen exposure significantly improves survival outcomes.