Hypersensitivity Reactions Overview organizes all four types of immune-mediated adverse responses into a structured classification system. Type I (Immediate/Allergic) involves IgE antibodies triggering mast cells; Type II (Cytotoxic) uses IgG/IgM antibodies against cell surfaces; Type III (Immune Complex-Mediated) deposits antigen-antibody complexes in tissues; Type IV (Delayed/Cell-Mediated) relies on sensitized T lymphocytes without antibodies. Each type includes its immunological mechanism and clinically relevant examples from anaphylaxis to contact dermatitis. This diagram serves as a quick reference for understanding pathophysiology and differential diagnosis of allergic and autoimmune conditions. Fork and customize this diagram to create study guides, clinical decision trees, or patient education materials.