The 3rd line of defense (Adaptive or acquired immunity) The Immune Response The 3rd line of defense (Adaptive or acquired immunity)

Specific Defenses The immune system Two properties 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) 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.

Antigens Antibodies HIV Virus Pollen

Antibodies Y-shaped proteins that bind foreign molecules (antigens) Produced by a white blood cell called the B cell

The immune response has two main parts: Humoral – involving antibodies Cell Mediated – involving white blood cells.

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) 3. 4.

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

T cells are floating in the circulation 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 (T h ) or effector cells recognize and bind to displayed antigen.

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.

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 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 Th release Interleukin II activating cytotoxic T cells Activated cytotoxic T cells destroy infected cells by puncturing their cell membranes. Cytotoxic T cells recognize antigens because they have complementary receptors on the surface of their cells.

Both the T cell and B cell response are regulated by helper T cells 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.