**Core Concept**
The process of transplant rejection involves a complex interplay between the immune system and the transplanted organ. The immune system recognizes the transplanted organ as foreign and mounts an immune response against it, leading to inflammation and damage to the organ.

**Why the Correct Answer is Right**
The correct answer is related to the role of T cells in transplant rejection. T cells, specifically CD4+ and CD8+ T cells, play a crucial role in the immune response against the transplanted organ. CD4+ T cells help activate other immune cells, while CD8+ T cells directly kill the cells of the transplanted organ. The correct answer highlights the importance of T cells in the rejection process.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while antibodies do play a role in transplant rejection, they are not the primary cause of rejection. Antibodies can form against the transplanted organ, but they are not as directly involved in the rejection process as T cells.
**Option B:** This option is incorrect because while cytokines do play a role in the immune response, they are not the primary cause of transplant rejection. Cytokines are signaling molecules that help coordinate the immune response, but they do not directly cause the rejection of the transplanted organ.
**Option C:** This option is incorrect because while the complement system does play a role in the immune response, it is not the primary cause of transplant rejection. The complement system helps eliminate foreign substances, but it is not as directly involved in the rejection process as T cells.

**Clinical Pearl / High-Yield Fact**
T cells are responsible for the majority of transplant rejection, and the use of immunosuppressive drugs to prevent T cell activation is a common strategy to prevent rejection.

**Correct Answer:** C. T cells play a crucial role in transplant rejection.