Medicine & USMLE

MHC I and II

  1. Innate Immunity
  2. Adaptive Immunity
  3. Macrophages
  4. Neutrophils
  5. Dendritic Cells
  6. Mast Cells
  7. Eosinophils
  8. Basophils
  9. Natural Killer Cells
  10. Antigens
  11. MHC I and II
  12. Antibodies
  13. B Lymphocytes Overview
  14. B Cell Stages
  15. B-Cell Activation
  16. Plasma B-Cells
  17. Memory B-Cells
  18. T-Lymphocytes Overview
  19. T-Cell Stages
  20. Types of Activated T-Cells


MHC, which is short for major histocompatibility complex, describes a group of membrane-bound proteins that display or present antigens for inspection by T-cells. There are two types of MHC: MHC-1 and MHC-2. MHC I displays endogenous antigens, or antigens from within the cell, while MHC II displays exogenous antigens, or antigens from outside the cell. These outside antigens are obtained by way of phagocytosis, so only phagocytes in the body have MHC-2. Finally, the presented antigens are inspected by T-cells, and if they are abnormal, the T-cell will initiate an immune response against the threat.

Key Points

  • MHC (Major Histocompatibility Complex) 1 vs 2
    • Surface proteins (membrane-bound) that present antigens for T-cells to inspect
    • Two types
      • MHC class 1 (MHC1)
        • Displays antigens derived from intracellular pathogens (viruses/bacteria)
      • MHC class 2 (MHC2)
        • Displays antigens derived from extracellular pathogens 
        • Displayed only by phagocytic cells