Medicine & USMLE

Cytotoxic (Killer) T Cells

B Cells and T Cells
  1. MHC I
  2. MHC II
  3. B Cells - Overview
  4. B Cells - Activation
  5. Plasma B Cells
  6. Memory B Cells
  7. T Cells - Overview
  8. T Cells - Activation
  9. T Cells - Differentation
  10. Cytotoxic (Killer) T Cells
  11. Helper T Cells - Overview
  12. Th1 Cells
  13. Th2 Cells
  14. Th17 Cells
  15. Regulatory T Cells (Tregs)


Killer T cells, also known as Cytotoxic T cells, are one of two main types of T-cells. Killer T-cells express CD8 on their surface, which is why they are also called CD8+ T-cells. Killer T-cells recognize antigens presented on MHC I. When these antigens are abnormal, such as in viral infections or cancer, Killer T-cells will kill the abnormal cell by releasing cytotoxic granules. These granules contain perforin and granzyme. Perforin works by forming holes in the target cell membrane, and granzyme enters the cell through these pores to cleave proteins -- ultimately resulting in cell death.

Key Points

  • Killer T Cells / Cytotoxic T Cells
    • Subtype of T lymphocyte in the adaptive immune system
    • Kills virus-infected, neoplastic, and donor graft cells
    • Express CD8 (also known as CD8+ T-cells)
    • Recognizes antigens presented on MHC I
      • Via T-cell receptor (TCR) with help of CD8
    • When activated by abnormal antigens, release cytotoxic granules containing perforin and granzyme
      • Perforin creates pore-like holes in the target cell membrane
      • Granzyme enters these holes and activates caspases and other proteases to induce apoptosis