This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunity, Subject name: Pathology
Which is true about type II hypersensitivity reaction? 
Select and explain. 
A. Immune complex mediated, B. Antigen - antibody mediated, C. Arthus phenomenon, D. Granulomatous reaction
B: Antigen - antibody mediated
Answer: B: Antigen - antibody mediated 
Explanation: Type II or Cytotoxic Hypersensitivity depends on the abnormal production of IgG or IgM directed against tissue antigens or a normal reaction to foreign antigens expressed on host cells. There are three main mechanisms of injury in Type II reactions:* Activation of complement followed by complement mediated lysis or phagocytosis and removal by leukocytes* Antibody dependent cellular cytotoxicity* Inactivation of a biologically active molecule