Which of the following antigens is most likely to be involved in hemolytic disease of the newborn?

Hemolytic disease of the newborn (HDN) often arises when there is an incompatibility between the blood types of a mother and her fetus, typically due to the presence of certain blood group antigens on the fetal red blood cells that the mother does not possess. The Kell antigen is one of the most clinically significant blood group systems involved in this scenario.

When a mother is Kell antigen-negative and the fetus inherits the Kell antigen from the father, the mother's immune system may recognize the fetal red blood cells as foreign. This can lead to the production of anti-Kell antibodies, which can cross the placenta and subsequently attack the fetal red blood cells, resulting in hemolytic disease. The severity of HDN can range from mild anemia to severe conditions, including hydrops fetalis or even stillbirth.

In contrast, the other antigens listed—Le^a, P1, and M—are generally not associated with significant cases of hemolytic disease of the newborn. They do not provoke the same robust immune response in the mother as Kell antigens do and are less likely to be involved in the pathophysiology of HDN. Therefore, Kell is the most relevant antigen in the context of hemolytic disease of the newborn,