AB type blood consists of RBCs having both 'a' and 'b' type antigens on their surfaces. Thus any possibility of cross reaction with any other similar peptide and generation of anti-A and anti-B is not possible, because self antigens do not elicit immune response and do not produce any antibody specific to them. read more
People with AB blood can form antibodies - there is no incapacity. They can be immunized and make the normal range of antibodies to pathogens and are in no way immunodeficient. They don’t make antibodies to other blood types (and are universal recipients), because they express both A and B antigens as “self” proteins and are thus tolerant to both. read more
The ABO blood type divides each blood type according to whether they have the "A" and "B" antigen(s) (AB has both, O has none). People also have antibodies against the antigens they don't have (AB has none, O has both), even before they have ever come in contact with those antigens. read more
Therefore, an individual with type AB blood can receive blood from any group (with AB being preferable), but cannot donate blood to any group other than AB. They are known as universal recipients. Blood group A individuals have the A antigen on the surface of their RBCs, and blood serum containing IgM antibodies against the B antigen. read more