The second class of damaging reactions is caused by specific antibody binding to cells or tissue antigens. The antibodies are of the IgM or IgG classes and cause cell destruction by Fc dependent mechanisms either directly or by recruiting complement via the classical pathway. Except where the reaction is autoimmune, the target cells are foreign to the host. In practise this means type II hypersensitivity reactions are usually only seen in blood transfusion recipients and patients with certain autoimmune diseases. The classic ABO incompatibility reaction is a type II, with IgM antibodies causing complement lysis of erythrocytes. Rhesus disease (or haemolytic disease of the newborn) is a special example since the IgG antibodies which cause destruction of foetal red blood cells by antibody dependent cellular cytotoxicity (ADCC) are passively acquired by the host via the placenta. You will hear more about these in the next lecture.
Because of cross-matching transfusion reactions are now rare, nevertheless sometimes IgG can exist for minor blood group antigens at a level sufficient to cause destruction of the transfused cells but too low to detect in vitro.
Click on either of these images to see a larger GIF version
Information provided by: http://www-immuno.path.cam.ac.uk