In general, production of an antibody against antigens that come from a different person of the same species. To a blood banker, this refers to the process of producing an alloantibody (targeting a red cell antigen that is absent from the red cells of the person making the antibody). This process is also called “isoimmunization” by clinicians (not so often by blood bank types). So, a blood banker might describe hemolytic disease of the newborn as resulting from maternal “alloimmunization” to paternal antigens, while a neonatologist might describe the same interaction as “isoimmunization.” No big deal, just different terms for the same process.

While the concept of alloimmunization is pretty easy to understand, the whole process is a little mysterious. For example, patients in certain groups are FAR more likely to become alloimmunized than others. The two diseases most famously associated with alloimmunization are sickle cell disease and warm autoimmune hemolytic anemia. Large proportions of patients with both of those diseases (conservatively, at least 30%), become alloimmunized, and that is a real problem for future transfusions (as well as for current transfusions, as delayed hemolysis can occur with alloimmunization). It is unclear exactly why these patients are so much more likely to make antibodies (listen to episode 30 of the BBGuy Essentials Podcast for more discussion on this issue in sickle cell patients).

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