NOTES: Specific Defenses / Immunity (UNIT 9 part 3)

ANTIGENS… ANTIGENS: specific foreign molecules that trigger an immune response; usually located on a cell’s surface -antigens include: proteinsglycoproteins polysaccharidesglycolipids toxins (venom, produced by bacteria)

ANTIGENS… lymphocytes develop receptors during embryonic development that allow them to differentiate between nonself (foreign) and self antigens nonself antigens combine with T cell and B cell surface receptors and activate these cells; this begins an immune reaction

LYMPHOCYTES (T and B Cells) originate in the red bone marrow some are released into the blood before they differentiate (specialize) -these reach the THYMUS, where they mature into T CELLS others, the B CELLS, mature in the RED BONE MARROW both T cells and B cells reside in lymphatic tissues and organs (lymph nodes, spleen, etc.)

LYMPHOCYTE FUNCTIONS **a lymphocyte must be ACTIVATED before it can respond to an antigen**

1) T CELLS ● some T cells interact with antigen-bearing cells directly = CELLULAR RESPONSE –Cytotoxic T cells ● some T cells secrete chemicals that enhance cellular response to antigens –Helper T cells

These chemicals can:  activate other T cells to divide and/or produce more chemicals  stimulate WBC production; cause B cells to grow/mature

1) T CELLS (continued) ● some T cells secrete toxins that kill their antigen-bearing target cells (cytotoxic T cells)

2) B CELLS ● B cells interact with antigen-bearing immune system cells, producing the HUMORAL IMMUNE RESPONSE (antibodies & memory cells for later) ● some B cells differentiate into PLASMA CELLS which produce ANTIBODIES

T and B cells… **each person has millions of varieties of T and B cells BUT only a few of each variety **once a specific cell has been activated, that cell CLONES itself to make lots of copies of the correct antigen fighting cell** **Therefore, each type of T cell or B cell has a particular type of antigen receptor that can respond only to a SPECIFIC antigen**

T CELLS and the CELLULAR IMMUNE RESPONSE * T cells are activated when an antigen- presenting cell displays a foreign antigen Antigen Presenting Cell (APC) antigen T cell!

T CELLS and the CELLULAR IMMUNE RESPONSE Example of T cell activation: 1) a macrophage engulfs and digests a pathogen 2) the macrophage displays the antigens on its cell membrane

3) the macrophage encounters a HELPER T CELL with the appropriate & specific antigen receptor  activates T cell 4) activated helper T cell divides & releases chemicals which stimulates the appropriate T cell (or the appropriate B cell to produce antibodies specific for the displayed antigen in the HUMORAL RESPONSE)

**Other T cells: CYTOTOXIC (KILLER) T CELLS: -recognize nonself antigens on cancer cells or virus-infected cells -once activated, it divides, enlarging its clone of cells -cytotoxic T cells then bind to the surfaces of the antigen-bearing cells, and release a protein (PERFORIN) that cuts openings in these cells, causing them to burst (LYSE)

A fully intact cancer cell surrounded by the immune systems killer t-cells. The cancer cell is surrounded and attacked by the killer T-Cells of the immune system. Scanning electron microscope pictures shows killer t-cells attacking the cancer cell. Notice the tentacles of the cancer cell. Notice how the cancer is completely flattened and totally destroyed. During the killing process, granules in a T-Cell fuse with the cell membrane and release units of the protein PERFORIN. These combine to form pores in the target cell membrane. Thereafter fluid and salts enter so that the target cell eventually bursts. Before…..…..After

B CELLS and the HUMORAL IMMUNE RESPONSE * B cells are activated when they encounter an antigen that fits its antigen receptors

B CELLS and the HUMORAL IMMUNE RESPONSE Example of B cell activation: 1) a B cell encounters an antigen (on a macrophage, bacteria, or Helper T cell) that fits its antigen receptors 2) the activated B cell divides, enlarging its clone (especially when stimulated by a helper T cell!)

3) activated B cells specialize into PLASMA CELLS (antibody-producing cells) *(antibodies react against the antigen that stimulated their production!)…more on this later AND 4) activated B cells also differentiate into MEMORY B CELLS (respond to subsequent exposures of the same antigen)

TYPES OF ANTIBODIES ● antibodies are proteins called IMMUNOGLOBULINS (Ig) ● 5 major types or classes of antibodies: IgG, IgA, IgM, IgD, and IgE.

IgG

ANTIBODY ACTIONS ● antibodies work by: 1)attacking the antigens directly (attaching to antigen) -cause them to clump together (AGGLUTINATION) or form insoluble masses (PRECIPITATE) -makes it easier for phagocytes to engulf the antigens / antigen-bearing agents & eliminate them

Agglutination

ANTIBODY ACTIONS 2) stimulate changes in local areas that help prevent the spread of the antigens (ex: promote inflammation)