American Board of Surgery Qualifying Exam (ABS QE) Practice Test

Acute rejection of a transplanted organ is mediated primarily by which type of cell?

1. B cells

2. T cells

3. Neutrophils

4. Monocytes

The correct answer is: T cells

Acute rejection of a transplanted organ is primarily mediated by T cells, specifically by the effector function of CD8+ cytotoxic T lymphocytes and CD4+ helper T cells. These T cells recognize foreign antigens presented by major histocompatibility complex (MHC) molecules on the surface of the transplanted tissue. During acute rejection, the T cells become activated and proliferate in response to the perceived threat posed by the histocompatibility differences between the donor and recipient. CD8+ cytotoxic T cells directly attack and destroy the transplanted cells, while CD4+ helper T cells help orchestrate the immune response by releasing cytokines that enhance the activity of other immune cells, including macrophages and B cells. The other cell types listed play different roles in the immune response. B cells are primarily involved in producing antibodies and dealing with humoral immunity, neutrophils play a key role in innate immunity, particularly in response to infections, and monocytes differentiate into macrophages and dendritic cells that are involved in both innate and adaptive immunity but are not the primary mediators of acute rejection. Thus, T cells are central to the mechanism of acute rejection in transplantation.