zoom on leukocytes

Immune System: Maturation and Differentiation

  • Maturation: the process of becoming mature.

  • Differentiation: modification to perform a specific function.

  • Cells involved in the immune response go through maturation and differentiation.

Key Immune Cell Types

Natural Killer Cells

  • Role: Important in killing cancer cells and virus-infected cells.

  • Mechanism: Attack directly without requiring prior sensitization to target cells.

B Cells (B Lymphocytes)

  • Purpose: Specialized lymphocytes that produce antibodies.

  • Maturation Process:

    • B cells differentiate into plasma cells.

    • Plasma cells produce specific antibodies targeting antigens.

  • Activation Location: Occurs in lymphoid tissues (lymph nodes, spleen, MALT).

    • MALT (Mucosal-associated lymphoid tissues): Includes tonsils.

  • Function:

    • Primarily effective against viruses and bacteria in the bloodstream.

    • Transformation occurs upon recognizing a specific antigen.

T Cells (T Lymphocytes)

  • Origin: Derived from the thymus (T stands for thymus).

  • Role: Directly kill infected or cancerous cells; involved in cell-mediated immunity.

  • Categories:

    • Helper T cells: Stimulate B cells and other immune cells.

    • Killer T cells: Destroy infected cells directly.

  • Comparison with B cells:

    • B cells are indirect killers (via antibodies).

    • T cells are direct killers (act on infected cells).

Immune System Types

  • Adaptive Immunity: Requires signaling from other immune cells (e.g., B and T cells).

  • Innate Immunity: Immediate response without prior exposure or signaling (e.g., natural killer cells).

Cytokines

  • Definition: Signaling proteins involved in immune responses.

  • Categories:

    • Interferons: Produced in response to antigens; slow viral replication, activating immune defenses.

    • Interleukins: Direct the proliferation and differentiation of B and T cells.

Overview of Immune Response

  • Initial Response to Infection:

    • Barrier breach (e.g., skin) leads to bacterial invasion.

    • Macrophages: First responders that engulf pathogens and initiate inflammation.

    • Neutrophils: Arrive to fight pathogens but may cause damage to healthy tissues.

  • Helper T Cells: Activate when antigen presentation occurs.

  • B Cells: Produce antibodies directed against the specific pathogen.

    • Plasma cells created from B cells rapidly produce large quantities of antibodies.

    • Memory cells formed for faster response during subsequent exposures.

Lymphatic System Components

  • Function: Drains excess fluid from tissues and transports lymph.

  • Structure:

    • Lymphatic vessels are open-ended; not a closed circuit like blood vessels.

    • Lymph nodes: Sites where pathogens are filtered and immune responses are activated (contains T cells, B cells, macrophages).

    • Major Organs:

      • Spleen: Filters blood, removes old erythrocytes, stores blood cells.

      • Thymus: Site for T cell maturation; size decreases with age.

      • Tonsils: Lymphoid tissues that help in trapping pathogens.

Antigen-Antibody Reaction

  • Definition: Binding of an antigen (foreign substance) to an antibody.

  • Role: Labels antigens for destruction by other immune cells.

  • Types of Antibodies:

    • IgG, IgA, IgM, IgD, IgE: Each has unique properties and locations within the body (e.g., IgG in blood, IgE in sinuses).

    • Different antibodies respond to various parts of the immune system.

Pathologies Related to the Lymphatic System

  • Lymphadenitis: Swollen lymph nodes due to infection/inflammation.

  • Lymphadenopathy: General enlargement of lymph nodes.

  • Lymphangioma: Tumor formed from abnormal lymph vessel collection.

  • Splenomegaly: Abnormal enlargement of the spleen.

  • Tonsillitis: Infection/inflammation of the tonsils.

  • Tonsillectomy: Surgical removal of the tonsils.