Final answer:
Hypersensitivity refers to the body's exaggerated immune response to harmless substances or self-antigens. Type I hypersensitivity is an immediate immune response mediated by IgE antibodies and mast cells. Type IV hypersensitivity is a delayed cell-mediated immune response.
Step-by-step explanation:
Hypersensitivity refers to the body's exaggerated immune response to harmless substances or self-antigens. There are different types of hypersensitivities, including immediate-type (allergy), delayed-type, and autoimmunity.
Type I hypersensitivity, also known as immediate hypersensitivity, occurs when a presensitized individual is exposed to an allergen, triggering a rapid immune response. This type of hypersensitivity is mediated by IgE antibodies and mast cells, resulting in symptoms such as sneezing, itching, and hives.
Type IV hypersensitivity, or delayed hypersensitivity, is a cell-mediated immune response that occurs one to two days after exposure. This type of hypersensitivity involves TH1 cytokines and may manifest as contact dermatitis or local tissue lesions.