Immune System Overview

Key Functions and Importance

• Protects humans from microorganisms, removes toxins, and destroys tumor cells.
• Immune response can identify threats, mount attacks, eliminate pathogens, and develop memory for future encounters.
• Response time: Typically within 10 days for most pathogens, but chronic responses may last longer.

Main Branches of the Immune System

• Innate Immune Response

  • Non-specific; cannot distinguish between different invaders.
  • Fast response (minutes to hours).
  • No memory formed, response is the same every time.
  • Includes chemical barriers (e.g., lysozyme in tears, low pH in stomach) and physical barriers (skin epithelium, cilia in airways).

• Adaptive Immune Response

  • Highly specific; recognizes unique parts of pathogens called antigens.
  • Diverse; can recognize almost infinite antigens.
  • Relies on cell activation and differentiation, taking weeks.
  • Includes immunologic memory for faster and stronger future responses.

White Blood Cells (Leukocytes)

• Hematopoiesis: Formation of blood cells in bone marrow.
  • Multi-potent hematopoietic stem cells differentiate into myeloid and lymphoid cells.

Myeloid Cells (Innate Immune Response)

• Neutrophils

  • Phagocytosis to ingest and destroy pathogens.
  • Use cytoplasmic granules and oxidative bursts.

• Eosinophils and Basophils

  • Contain granules with histamine.
  • Involved in allergy and parasite responses.

• Mast Cells

  • Similar to basophils; involved in allergic responses.

• Monocytes, Macrophages, Dendritic Cells

  • Antigen-presenting cells (APCs).
  • Phagocytosis and cytokine release to attract other immune cells.

Lymphoid Cells (Adaptive Immune Response)

• B Cells

  • Bind to antigens directly.
  • Present antigens to T cells.
  • Mature into plasma cells to secrete antibodies (humoral immunity).

• T Cells

  • CD4 (Helper T cells): Coordinate immune response and help B cells.
  • CD8 (Cytotoxic T cells): Kill infected cells presenting antigens on MHC I.

• Natural Killer (NK) Cells

  • Part of innate immunity.
  • Target virus-infected and cancer cells.

Immune Response Process

1. Pathogen breaches physical and chemical barriers.
2. Innate immune cells (e.g., macrophages) ingest pathogens and release cytokines.
3. Dendritic cells present antigens to T cells in lymph nodes.
4. T cells differentiate and proliferate, assisting B cells to produce antibodies.
5. Pathogen targeted and eliminated through coordinated immune attack.
6. Memory cells remain for rapid response upon future exposure.

Summary

• Innate response: Immediate, non-specific, no memory.
• Adaptive response: Specific, develops memory, slower start but more effective.