**Core Concept**
Acute hemolytic transfusion reaction (AHTR) is a life-threatening condition caused by the rapid destruction of red blood cells (RBCs) due to an immune response. This occurs when pre-existing antibodies in the recipient's plasma bind to foreign antigens on the transfused RBCs, leading to their destruction.

**Why the Correct Answer is Right**
The primary culprit behind AHTR is the ABO blood group system, specifically the A and B antigens. These antigens are present on the surface of RBCs and are recognized by pre-formed IgM antibodies in the recipient's plasma. When ABO-incompatible blood is transfused, these antibodies bind to the A or B antigens on the RBCs, marking them for destruction, primarily through the complement pathway. This leads to a rapid and severe hemolytic reaction.

**Why Each Wrong Option is Incorrect**
* **Option A:** HLA (Human Leukocyte Antigen) antibodies are responsible for graft-versus-host disease and transfusion-related acute lung injury, but not typically for AHTR.
* **Option B:** RhD antibodies can cause hemolytic disease of the newborn (HDN) and, in rare cases, AHTR, but the ABO blood group system is the primary concern in transfusion medicine.
* **Option C:** Kell antibodies can also cause hemolytic disease of the newborn and, in rare cases, AHTR, but are less common than ABO antibodies.

**Clinical Pearl / High-Yield Fact**
Always verify the ABO blood group and RhD type of the recipient and donor before transfusing blood to prevent AHTR. ABO-incompatible blood transfusions are a medical emergency and require immediate attention.

**Correct Answer:** B. RhD antibodies.