Final answer:
Type II hypersensitivities are characterized by cell lysis or cytotoxicity, which occurs when antibodies react with antigens on cell surfaces, leading to cell destruction through complement activation or ADCC.
Step-by-step explanation:
Type II hypersensitivities are characterized by cell lysis (cytotoxicity) caused by antibodies binding to antigens on cells. This response is mediated by immune reactions involving IgG and IgM antibodies that target cell-surface or matrix-associated antigens.
In contrast to Type I hypersensitivity, which involves mast cell degranulation due to allergen-specific IgE, Type II hypersensitivity reactions lead to an inflammatory response and cell lysis through mechanisms such as complement activation or antibody-dependent cell-mediated cytotoxicity (ADCC). These reactions can be severe, as seen in conditions like hemolytic transfusion reactions and hemolytic disease of the newborn, where the immune system attacks the red blood cells leading to their destruction.