Immune System Components

The immune system is a complex network of cells and proteins that defends the body against pathogens. Key players include B and T lymphocytes, antibodies, and various immune cells that work together to recognize and eliminate threats, ensuring our health.

1. B lymphocytes (B cells)

   • Develop in the bone marrow and are crucial for the humoral immune response.
   • Differentiate into plasma cells that produce antibodies.
   • Memory B cells remain after infection, providing long-term immunity.

2. T lymphocytes (T cells)

   • Mature in the thymus and are essential for cell-mediated immunity.
   • Include helper T cells (CD4+) that assist other immune cells and cytotoxic T cells (CD8+) that kill infected cells.
   • Play a role in recognizing and responding to specific antigens.

3. Antibodies

   • Proteins produced by B cells that specifically bind to antigens.
   • Neutralize pathogens, opsonize for phagocytosis, and activate the complement system.
   • Exist in different classes (IgG, IgA, IgM, IgE, IgD) with distinct functions.

4. Antigens

   • Molecules or parts of pathogens that are recognized by the immune system.
   • Can be proteins, polysaccharides, or other substances that trigger an immune response.
   • Help in the activation of B and T cells.

5. Macrophages

   • Large phagocytic cells that engulf and digest pathogens and debris.
   • Present antigens to T cells, linking the innate and adaptive immune responses.
   • Secrete cytokines to recruit and activate other immune cells.

6. Neutrophils

   • The most abundant type of white blood cell, crucial for the innate immune response.
   • Rapidly respond to sites of infection and are effective at phagocytosing bacteria.
   • Release enzymes and reactive oxygen species to kill pathogens.

7. Natural killer cells

   • A type of lymphocyte that plays a role in the innate immune response.
   • Recognize and destroy infected or cancerous cells without prior sensitization.
   • Release cytotoxic granules that induce apoptosis in target cells.

8. Dendritic cells

   • Antigen-presenting cells that capture and process antigens for T cell activation.
   • Found in tissues and migrate to lymph nodes to stimulate adaptive immunity.
   • Act as a bridge between the innate and adaptive immune systems.

9. Complement system

   • A group of proteins that enhance the ability of antibodies and phagocytic cells to clear pathogens.
   • Can directly lyse pathogens, promote inflammation, and opsonize targets for phagocytosis.
   • Activated through three pathways: classical, lectin, and alternative.

10. Major histocompatibility complex (MHC)

    • Molecules on cell surfaces that present antigens to T cells.
    • MHC class I presents to CD8+ cytotoxic T cells, while MHC class II presents to CD4+ helper T cells.
    • Critical for self-recognition and immune response regulation.

11. Cytokines

    • Signaling proteins released by immune cells that mediate and regulate immunity and inflammation.
    • Include interleukins, interferons, and tumor necrosis factors.
    • Play roles in cell communication, activation, and differentiation.

12. Lymph nodes

    • Small, bean-shaped structures that filter lymph fluid and house immune cells.
    • Sites where B and T cells encounter antigens and initiate immune responses.
    • Swell during infections due to increased immune activity.

13. Thymus

    • An organ where T cells mature and differentiate.
    • Involved in the selection process to ensure T cells can recognize self-MHC and foreign antigens.
    • Shrinks with age, impacting immune function.

14. Spleen

    • An organ that filters blood and helps mount immune responses to blood-borne pathogens.
    • Contains white pulp (immune function) and red pulp (removal of old red blood cells).
    • Acts as a reservoir for immune cells.

15. Bone marrow

    • The primary site of hematopoiesis, where all blood cells, including B cells, are produced.
    • Contains stem cells that differentiate into various immune cells.
    • Essential for the development and maturation of B cells.