What is the significance of human leukocyte antigens (HLAs)?

• A. They help the body determine self vs. non-self and indicate a person's tissue type.
• B. They determine blood type.
• C. They predict response to chemotherapy.
• D. They are used only in blood transfusions.

Answer: (A)

HLAs are part of the major histocompatibility complex and sit on the surface of nearly all nucleated cells, including antigen-presenting cells. Their main job is to display peptide fragments to T cells, allowing the immune system to distinguish what belongs to the body from what doesn’t. Because HLA genes are highly diverse, each person has a unique tissue-type fingerprint. This makes HLA typing crucial for transplantation: matching donor and recipient HLAs helps prevent immune rejection and complications like graft-versus-host disease.

This isn’t about blood type, which is determined by ABO and Rh antigens on red blood cells. HLAs govern tissue compatibility and immune recognition across various tissues, not just transfusions.