Basic and Clinical Sciences (BCSE) Practice Exam

A Type II hypersensitivity reaction is characterized by cytotoxic action involving antibodies that target specific cellular antigens. This response often leads to the destruction of cells that have surface markers recognized as foreign by the immune system. The antibodies involved in this reaction are typically of the IgG or IgM type. They bind to antigens on the surface of cells, marking them for destruction by mechanisms such as opsonization, complement activation, or antibody-dependent cell-mediated cytotoxicity (ADCC). Common clinical examples include hemolytic anemia and blood transfusion reactions, where the body's immune system attacks its own red blood cells due to the presence of incompatible antigens.

The other types of hypersensitivity reactions are distinct. The first option refers to an IgE mediated response, which is typical of Type I hypersensitivity, where allergens trigger mast cells to release histamine and other inflammatory mediators. The third option describes Type IV hypersensitivity, which is mediated by T-cells instead of antibodies and is associated with delayed-type reactions. The last option pertains to mucosal immunity, often associated with IgA responses, which does not reflect the cytotoxic antibody-driven mechanism characteristic of Type II reactions.