The antigens of the ABO system are mimicked by bacterial cell walls. So if your body does not actively suppress antibodies to them (because you have them) then antibodies will form over time to the ones you so not have (A or B or both).
The rhesus factor (Rh) is not mimicked in nature and so antibodies are not formed in Rh negative people until after an exposure - usually when an Rh negative women carries an Rh positive child. If the person is Rh positive then antibodies will not form no matter what.
The blood given by transfusion must be matched with the recipient's blood type. Incompatible blood types can cause a serious adverse reaction (transfusion reaction). Blood is introduced slowly by gravity flow directly into the veins
Acute immune hemolytic reaction
Most severe type, but rare incompatible blood incompatibility in multiple transfusions. Mostlikely to occurs when transfused red cells react with circulating antibody in the recipient with resultant intravascular hemolysis. When a group O patient is mistakenly transfused with group A, B, or AB blood. Patients receiving a major ABO- incompatible marrow or stem cell transplant with sufficient red cell content will likely develop an acute hemolytic reaction. Symptoms are: fever, chills and fever, the feeling of heat along the vein in which the blood is being transfused, pain in the lumbar region, constricting pain in the chest, tachycardia, hypotension, and hemoglobinemia with subsequent hemoglobinuria and hyperbilirubinemia. Prevention: proper identification of patients, pre-transfusion blood samples and blood components at the same time of transfusion.
Risks associated with autologous blood transfusion include transfusion reaction if an allogeneic blood transfusion was inadvertently given and transmission of infectious agents if the blood became contaminated.
These complications may include an acute hemolytic transfusion reaction (AHTR), which is most commonly caused by ABO incompatibility. The patient may complain of pain, difficult breathing, fever and chills, facial flushing, and nausea.
No Reaction At All.
Two or more materials are said to be chemically incompatible when they cannot exist in each other's or one another's mutual contact for more than a few minutes without commencing a chemical reaction between or among themselves.
Sometimes problems occur with a blood transfusion, but that is supposed to be rare. Some people can have an allergic reaction to the transfusion.
monitor the treatment
Every blood transfusion carries the risk of allergic reaction, to anaphylactic shock, even if blood type is perfectly matched. If medication was also infused along with the blood, and the patient had an allergic reaction, it would be impossible to tell which sustance was causing the reaction: the blood? or the medication? Remember that every transfusion reaction can be deadly. As well, some meds may break down blood components. Therefore, never inject IV meds into a transfusion tubing or combine medications into a blood transfusion set.
Complement Fixation
"Adverse" means harmful or unfavorable, and transfusion probably refers to blood transfusion--so a negative reaction to a blood transfusion? The term is very vague; without context it's hard to say exactly what this would mean.