[A toddler with a red, swollen arm after vaccination]

Overview

Overview

Anaphylaxis is a severe, life-threatening hypersensitivity reaction mediated by Immunoglobulin E (IgE) antibodies. When IgE binds to allergens, it triggers the release of mediators– histamine, leukotrienes, and prostaglandins from mast cells and basophils. These mediators cause vasodilation, edema, and inflammation, leading to various symptoms.The primary allergens causing anaphylaxis include food items (e.g., peanuts, shellfish), drugs (e.g., penicillin, asparaginase, corticotropin,...

Type III hypersensitivity reactions occur when antigen–antibody complexes form and activate the complement system. Normally, these complexes help the clearance of antigens by phagocytes and red blood cells. However, when large numbers of immune complexes are present, they can deposit in tissues—particularly in the walls of blood vessels—leading to inflammation and tissue injury. These deposits trigger complement activation and neutrophil recruitment, resulting in serum...

Diphtheria is an acute, toxin-mediated infectious disease that primarily affects the upper respiratory tract. It is caused by Corynebacterium diphtheriae, a Gram-positive, pleomorphic rod that lacks spore-forming capability and exhibits a characteristic club-shaped morphology under microscopic examination. While C. diphtheriae can asymptomatically colonize mucosal surfaces, clinical disease manifests only when the bacterial strain is lysogenized by a specific β-corynephage. This phage...

Allergic reactions related to drugs are hypersensitivity responses driven by the immune system and bear no connection to the drug's therapeutic action. While drugs in isolation do not trigger an immune response, they can interact with endogenous proteins to form antigens. These antigens stimulate lymphocytes to produce antibodies. IgE-type antibodies attach themselves to mast cells. Upon subsequent exposure to the same stimulus, the antigen-antibody interaction is initiated, unleashing...