Question

Who can AB positive give blood to?

Answer 1

The presence or absence of the antigens A and B, which are carried on the surface of red blood cells, determines the ABO blood group system, which classifies human blood based on the hereditary characteristics of red blood cells (erythrocytes). As a result, people might have blood types A, B, O, or AB. Karl Landsteiner, an Austrian immunologist, was the first to discover the A, B, and O blood groups.

Complete answer:
AB positive can give blood only to AB positive. This can be understood as follows:
Since individuals with AB positive blood groups have all A, B and Rh antigens they can give blood to AB positives.
In case they give blood to individuals who have a negative blood group there would be a blood transfusion reaction due to the antibodies for Rh present in the recipient.
Similarly, if they donate blood to O positives there would again be a blood transfusion hemolytic reaction because of the antibodies for A and B antigens present in the recipient body.
Also, if they donate blood to A positives, again a blood transfusion hemolytic reaction will occur due to antibodies formed by the recipient body against B antigens.
As mentioned above, individuals with AB positive blood type could not donate blood to B positives as well.

Note:
After a blood transfusion, a hemolytic transfusion response is a severe complication that can develop. The response happens when the person's immune system destroys the red blood cells supplied during the transfusion. Hemolysis is the term used for the process of destroying red blood cells in a transfusion reaction. A blood transfusion between compatible groups (such as O$+$ to O$+$) does not cause any reaction.