What is the target antigen in alloimmune hypersensitivity reactions?

• A. The recipient's own cells
• B. Allergens from the environment
• C. Cells or tissues from another individual
• D. Pathogens causing infections

Answer: (C)

In alloimmune hypersensitivity reactions, the target antigen is cells or tissues from another individual. This type of immune response is typically seen in situations such as organ transplants, where the recipient's immune system recognizes the donor's cells as foreign due to differences in their antigenic profiles, especially Human Leukocyte Antigen (HLA) markers. The immune system responds by mounting an attack against these foreign cells, which can lead to rejection of the transplanted tissue or organ.

The other options do not pertain to the nature of alloimmune hypersensitivity. The recipient's own cells are involved in autoimmune reactions, where the immune system mistakenly targets its own tissues. Allergens from the environment are associated with allergic reactions, which are typically IgE-mediated hypersensitivity responses. Pathogens causing infections trigger innate and adaptive immune responses but are not the focus of alloimmune hypersensitivity, which specifically deals with the immune response to non-self tissues from another human.