Immune system ↗Allergen crosses a susceptible interface
Pollen, food, venom, medicines, mites, animals, molds, occupational material, and other antigens enter distinct barrier tissues.
IMMUNE / 10
Harmless input.
Costly response.
Allergy develops when immune memory targets an otherwise usually harmless substance. IgE-mediated reactions are important but not the only allergy mechanism, and asthma includes multiple inflammatory and nonallergic phenotypes.
Barrier alarms shape type-2 context
Epithelial cytokines and dendritic-cell activation can favor helper T-cell programs associated with allergy and barrier repair.
Helper signals instruct B cells
Type-2-associated cytokines and cell contact support class switching toward IgE in susceptible contexts.
Allergen-specific IgE is produced
Plasma cells secrete IgE that binds high-affinity FcεRI receptors on mast cells and basophils.
Memory can exist without symptoms
Specific IgE or a positive test indicates sensitization but does not alone prove clinically important allergy.
Allergen activates armed mast cells
Multivalent allergen binds adjacent mast-cell IgE molecules, initiating rapid signaling and granule release.
Fast symptoms appear
Histamine can cause itch, hives, sneezing, vascular leak, nasal symptoms, gut effects, and selected smooth-muscle responses.
Leukotrienes and prostaglandins extend effects
Newly synthesized mediators contribute to bronchoconstriction, mucus, edema, and recruitment beyond the immediate granule phase.
Eosinophils and T cells arrive
Cytokines and chemokines recruit eosinophils and other cells that can sustain epithelial injury and reactivity for hours or days.
Multiple systems can fail rapidly
Airway swelling, bronchospasm, vasodilation, vascular leak, low pressure, and gastrointestinal symptoms can create a life-threatening emergency.
Airways narrow too readily
Inflamed or sensitized airways contract excessively to allergens, infection, exercise, cold air, irritants, or other triggers.
Smooth muscle raises resistance
Airway muscle contraction rapidly narrows caliber, especially affecting expiratory flow and producing uneven ventilation.
The lumen narrows further
Secretions, epithelial shedding, and wall swelling add obstruction while cough and clearance mechanisms change.
Repeated inflammation can alter structure
Smooth-muscle mass, basement-membrane-associated matrix, glands, vessels, and epithelial behavior can change over time.
One mediator can be blocked
H1 antihistamines reduce selected histamine symptoms but do not treat all asthma biology or substitute for emergency anaphylaxis care.
Airway targets differ by phenotype
Inhaled corticosteroids, bronchodilators, leukotriene modifiers, and targeted biologics act at different stages and require an individualized plan.