Overview of the Immune System

Introduction

• Exploring one body system in depth is remarkable.
• The immune system is fascinating due to its constant work against pathogens.
• Pathogens include viruses, bacteria, fungi, protists, and parasitic worms.
• External protections like skin and mucous membranes act as the first line of defense.
• The first line of defense is nonspecific.

Second Line of Defense: Inflammatory Response

• Activated when pathogens breach the first line of defense.
• Example: Stepping on a sharp stick introduces bacteria.
• Mast cells release histamine causing
  • Blood vessels to dilate and become leakier.
  • Easier access for white blood cells (e.g., macrophages) to reach the area and consume pathogens.
• Complement system complements immune actions and attracts macrophages.
• This is also a nonspecific response.

Third Line of Defense: Specific Response

• Targets specific pathogens through adaptive immunity.
• More complex; features additional details and exceptions.

Adaptive Immunity

• Specific response to antigens recognized as non-self.
• Divided into cell-mediated and humoral responses.

Cell-Mediated Response

• Involves Cytotoxic T cells that destroy infected cells via apoptosis.
• Cytotoxic T cells are activated by infected cells presenting antigens or signals from macrophages.
• Helper T cells aid in this activation process.

Humoral Response

• Involves B cells that produce antibodies.
• Antibodies bind to specific antigens to deactivate pathogens and signal macrophages.
• B cells activated by Helper T cells or free antigens.

Memory Cells

• Memory B cells and Memory T cells retain information about antigens.
• Memory B cells can activate Plasma B cells to produce antibodies.
• Memory T cells can activate Cytotoxic T cells to attack infected cells.
• Basis for vaccination: introduces inactive or weakened pathogen to create memory cells without causing disease.

Conclusion

• The immune system is incredibly complex and powerful.
• Encourages further exploration and study.