Which of the following is true regarding transplant rejection?

Transplant rejection primarily occurs when the recipient's immune system recognizes the donor tissue as foreign and mounts an immune response against it. This process involves various immune cells, particularly T lymphocytes, which attack the transplanted tissue because it does not have the same human leukocyte antigens (HLAs) as the recipient. This recognition leads to inflammation and, ultimately, damage or destruction of the transplanted organ.

The other options do not align with the established understanding of transplant rejection. The notion that the donor rejects the recipient's tissue is not how transplant rejection works; rather, it is the recipient's immune system that responds. The idea that no immunological response occurs contradicts the fundamental nature of transplant immunology, where a robust immune response is expected. Lastly, while there can be varying degrees of immune response, referring to it as a low-level response misses the significant immune activation that typically arises in transplant settings, particularly if the donor and recipient are not well-matched.