Production of an antibody against antigens that come from a different person of the same species. Clinicians tend to like this term, especially neonatologists, but blood bankers tend to use our very own term: “Alloimmunization,” which means the same thing. So, a blood banker might describe hemolytic disease of the fetus/newborn as resulting from maternal “alloimmunization” to paternal antigens, while a neonatologist might describe the same interaction as “isoimmunization.” No biggie, just different terms for the same process.