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The Immune Response. The 3 rd line of defense (Adaptive or acquired immunity). Specific Defenses. The immune system Consists of a large number of cells that work together to respond to a specific microbe or foreign invader. Two properties

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The Immune Response

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The immune response

The Immune Response

The 3rd line of defense

(Adaptive or acquired immunity)

Specific defenses

Specific Defenses

  • The immune system

    • Consists of a large number of cells that work together to respond to a specific microbe or foreign invader.

  • Two properties

    • Specificity for particular foreign molecules (antigens)

    • Memory for previously encountered antigens

Definitions see vocab sheet

Definitions (see Vocab sheet)

  • Antigens

    • Are foreign substances that trigger an immune response

    • Most are pathogens

  • Antibodies

    • Are proteins found in blood plasma that attach to one particular kind of antigen and mark it for destruction.

The immune response

  • Antigens

  • Antibodies

HIV Virus




  • Y-shaped proteins that bind foreign molecules (antigens)

    • Produced by a white blood cell called the B cell

The immune response

  • The immune response has two main parts:

    • Humoral – involving antibodies

    • Cell Mediated – involving white blood cells.

The 4 cells involved in the immune response

The 4 cells involved in the immune response

  • Macrophages/Dendritic cells

  • Cytotoxic (Killer) T Cells

  • B Cells – Plasma and Memory cells

  • Helper T Cells (Effector cells)



Humoral antibody mediated response

Humoral (antibody mediated) Response

  • Macrophages/dendritic cells phagocytose microbes.

  • Some of the digested material (antigen) is then displayed on the surface of the macrophage/dendritic cell.

  • This allows the immune system to recognize the invader and become activated.

  • The process is known as: Antigen Presentation

The immune response

  • T cells are floating in the circulation. They carry receptors on the surface of their cell that are complementary to the antigen being presented.

  • T helper cells (Th ) or effector cells recognize and bind to displayed antigen.

The immune response

  • This binding causes macrophages to release Interleukin I.

  • Interleukin I causes Th cells to release Interleukin II

  • Interleukin II stimulates division of Th cells and cytotoxic T cells, amplifying body response to infection.

The immune response

  • Interleukin II released by Th cells also activates B cells.

  • Activated B cells divide and develop in to Plasma cells that release Y shaped antibodies into the blood.

  • Antibodies will bind to a specific antigen (the one originally presented by macrophage)

The immune response

  • The binding of antibodies causes antigens to stick together, forming clumps that can be easily identified and destroyed by macrophages.

  • B cells also divide into memory cells which will be rapidly activated if presented with same antigen in the future.

Cell mediated response

Cell Mediated Response

  • Th release Interleukin II activating cytotoxic T cells

  • Activated cytotoxic T cells destroy infected cells by puncturing their cell membranes.

  • CytotoxicT cells recognize antigens because they have complementary receptors on the surface of their cells.

The immune response

  • Both the T cell and B cell response are regulated by helper T cells. Both responses happen simultaneously.

  • Both B and cytotoxic T cells create memory cells.

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