An antigen occurring on the red blood cells of many humans (around 85 per cent) and some other primates. It is particularly important as a cause of haemolytic disease of the newborn and of incompatibility in blood transfusions.
 Example sentencesExamples
-  There are also subsidiary blood proteins such as the rhesus factor that can be positive or negative (absent).
 -  The rhesus factor protein is the next most important one after the A and B proteins.
 -  The discovery of the rhesus factor in human blood by American scientists also had important implications for blood grouping and, ultimately, for the development of human genetics.
 -  Anti-D injections are used to counteract the rhesus factor if it proves necessary after a blood test.
 -  Treatment for women with rhesus factor disease (where the Rh blood groups of the mother and baby do not match) is essential.