Medicine & USMLE


  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


Antibodies are Y-shaped proteins produced by B-cells of the adaptive immune system. As a key player in our immune system’s humoral response, antibodies recognize and bind to antigens either as freely circulating proteins or as membrane-bound proteins. The antibody is made up of 2 light chains and 2 heavy chains, which come together to form variable regions on one end and a constant region on the other. The variable region is responsible for binding a wide variety of antigens, while the constant region works to alert other parts of our immune system to destroy whatever is bound by the antibody.

Key Points

  • Antibodies (Immunoglobulins)
    • Main component of the humoral response of the adaptive immune system
    • Y-shaped proteins
    • Recognize and bind antigens
      • Binding to antigens attracts innate immune cells to phagocytose and destroy the pathogen
    • Produced by B cells
      • Each B cell makes a single type of antibody or immunoglobulin, which can recognize and bind to a specific antigen 
      • Can exist as membrane-bound cell receptors or independently in circulation 
    • Structure of an antibody
      • Two identical heavy chains and light chains
        • Connected by disulfide bonds
      • Both heavy and light chain involved in forming:
        • Constant region
          • Does not bind antigens
          • Signals to other cells (eg, phagocytes) and proteins to destroy antigen bound at other end
        • Variable region
          • Binds antigen
          • Unique amino acid structure of this region determines specificity of antibody