Lecture Notes: Second Line of Defense

Overview

• Purpose: Discuss the second line of defense in the immune system, activated when the first line (skin barrier) is breached.
• Components:
  • Antimicrobial proteins
  • Specialized cells
  • Specific processes

Antimicrobial Proteins

1. Transferrin

   • Found in blood, related to iron transport.
   • Prevents pathogens from using iron for metabolism.
   • Iron attached to transferrin is not available for pathogen use.

2. Interferon

   • Types include alpha, beta, etc.
   • Mechanism:
     • Virus infects cell, turning it into a virus-making factory.
     • Infected cell releases interferon, affecting neighboring cells.
     • Interferon doesn't prevent infection but interferes with viral replication.
     • Protects neighboring cells from turning into virus factories.

3. Complement Proteins

   • Series of over 20 proteins enhancing immune reactions.
   • Operate as a cascade, similar to blood clotting mechanisms.

Specialized Cells

1. Natural Killer Cells (NK Cells)

   • Lymphocytes, not T cells.
   • Part of immune surveillance, identifying cells without correct MHC markers.
   • Recognize and kill cells not marked as "self."

2. Phagocytic Cells

   • Includes neutrophils and macrophages.
   • Eosinophils have minor phagocytic abilities.

Additional Considerations

• Major Histocompatibility Complex (MHC):
  • Cellular markers identifying "self."
  • Essential for immune system to recognize and protect own cells while targeting foreign ones.
  • Important in transplant rejection, requiring anti-rejection drugs.

Conclusion

• The second line of defense includes critical components like antimicrobial proteins and specialized cells that work together to protect the body from pathogens that bypass initial barriers.