The unexpected antibodies with primary importance are;

1. Immune Alloantibodies - which are produced in response to red blood cell (RBCs) stimulation through transfusion, transplantation, or pregnancy. 2. Naturally Occurring Antibodies - may form as a result of exposure to environmental sources, such as pollen, fungus, and bacteria, which have structures similar to some RBC antigens. 3. Passively Acquired Antibodies - Antibodies produced in one individual and then transmitted to another via plasma-containing blood components or derivatives such as intravenous immunoglobulin (IVIG)