Immunology Lecture: Nonspecific Defense Mechanisms

Overview of Nonspecific Defense

• Phagocytes: Cells that recognize and engulf pathogens.
  • Recognize proteins or markers on pathogens.
  • Engulf and surround the pathogen with a membrane.
  • The membrane forms a structure called phagosome.

Types of Phagocytes

• Macrophages
• Neutrophils
• Dendritic cells

Process of Phagocytosis

1. Pathogen recognition and engulfment.
2. Formation of phagosome.
3. Fusion with lysosome to digest the pathogen.

Lysosome Fusion

• Lysosomes bond to phagosome.
• Release enzymes to break down the pathogen into smaller molecules.

Antigen Presentation

• Short chains of peptides bind to special proteins.
• These proteins transport to the cell membrane.
• Present parts of the pathogen on the cell surface.
  • These proteins are called major histocompatibility complexes (MHC).
  • Specifically, MHC Class II in phagocytes/macrophages/dendritic cells.

Role of B Cells

• Part of the adaptive immune system.
• Membrane-bound antibodies specific to certain pathogens.
• Activation Process:
  • Pathogen binds to B cell via epitope.
  • Activation usually requires helper T cells.
  • Engulfment of pathogen by B cell.
  • Proliferation into plasma and memory B cells.

Plasma B Cells

• Produce and release antibodies targeting specific pathogens.

Memory B Cells

• Retain information about the pathogen for future responses.

Similar Processes in B Cells

• B cells also present antigens on their surface with MHC Class II proteins.

Professional Antigen Presenting Cells

• Cells that engulf, digest, and present antigens are called professional antigen-presenting cells.
• Includes phagocytes and B cells.

Importance in Immune System

• MHC II proteins are recognized by helper T cells.
• Key to activating the immune response.

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Next Topic

• MHC Class I presenting cells will be covered in subsequent lectures, focusing on their role in immune responses.