Download NOTES: Specific Defenses / Immunity (Ch 14, part 3)

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:
proteins
glycoproteins
polysaccharides
glycolipids
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 antigenpresenting cell displays a foreign
antigen
antigen
Antigen
Presenting
Cell
(APC)
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)
Before…..…..After
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.
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)