Download Chapter 39 - The Body Defenses

Chapter 39 - The Body Defenses
Immunity - refers to the body’s ability to resist or eliminate potentially harmful foreign
material s or abnormal cells
Mechanisms include:
1. Defense against invading pathogens (disease-producing microorganisms such as
viruses & bacteria) - major targets of the immune system
2. Removal of “worn-out” cells & tissue debris
3. Identification & destruction of abnormal or mutant cells
4. Allergies & autoimmune responses
5. Rejection of tissue cells of foreign origin
Chapter 39 - The Body Defenses
Immune system cells
1. Neutrophils - mobile, phagocytic specialists
2. Eosinophils - secrete chemicals toxic to pathogens
3. Basophils - secrete histamine & heparin
4. Monocytes -phagocytes
5. Lymphocytes
A) B lymphocytes (B-cells) which are transformed into plasma cells, which
secrete antibodies that indirectly lead to the destruction of the foreign
material
B) T lymphocytes (T-cells) which are transformed into cytotoxic T-cells,
which directly destroy virus-invaded cells & mutant cells via
nonphagocytotic means
Chapter 39 - The Body Defenses
Immune responses are either nonspecific or specific
Nonspecific immune response
1. Inflammation - neutrophils & monocytes play a major role
2. Interferon - a family of proteins that nonspecifically defend against viral infection
3. Natural killer cells - a special class of lymphocyte-like cells that spontaneously lyse
(destroy) virus-infected host cells & cancer cells
4. The complement system - a group of inactive plasma proteins that when activated
attack & destroy the plasma membranes of foreign cells
Inflammation
Goal of the inflammatory response is to bring to the invaded or injured area phagocytes
& plasma proteins that:
1. Isolate, destroy, or inactivate the invader
2. Remove debris
3. Prepare for subsequent healing & repair
4. Phagocytes secrete endogenous pyrogen which induces a fever
Chapter 39- Blood
Chapter 39- Blood
Chapter 39 - The Body Defenses
Interferon
Released from virus-infected cells
Inhibits multiplication of viruses in most cells
Mechanism
Virus enters first cell, & this cell releases interferon as a response
Interferon binds with receptors on uninfected cells, & initiates the production of
inactive enzymes capable of breaking down viral RNA
Once the virus enters this “primed” cell, the enzymes are activated & the viral RNA is
destroyed - virus is DEAD!
Chapter 39 - The Body Defenses
Natural killer cells
Naturally occurring, lymphocyte like cells that lyse virus-infected cells
Complement system
Circulating plasma proteins (9) in an inactivated form
When activated, complement proteins 5 - 9 will combine & insert themselves into the
cell membrane of a target cell, lysing it
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Chapter 39 - The Body Defenses
Specific Immune Response
Divided into:
1. Humoral (antibody-mediated) immunity
2. Cell mediated immunity
How is the specific immune response stimulated?
Antigens are molecules that stimulate the immune response to attack it
Antigenic determinant sites are found on complex antigens & may stimulate the
immune system to attack it with multiple antibodies
Chapter 39 - The Body Defenses
Humoral immunity
Antibodies are the attackers for this immune response
Secreted by plasma cells which are produced via B-cell differentiation
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Chapter 39 - The Body Defenses
Antibody structure
Composed of 2 heavy chains & 2 light chains linked together = arranged in a “Y”
Tips of the”Y” = antigen binding fragments (Fab)
Tail portion = constant region (Fc) - interacts with immune cells
Antibody actions
1. Neutralization - antibodies bind with bacterial toxins or viruses, preventing them
from interacting with cells
2. Agglutination “clumping” & precipitation “insoluble” - prevent proper functioning
- minor action - more important in diagnostics
3. Activation of complement system - activation of complement system proteins which
attack the cell membrane of the invading cell
4. Enhancement of phagocytosis - antibody tails bind with phagocytes
5. Stimulation of Killer cells (non-specific) - recognize antibody tails
Chapter 39 - The Body Defenses
Cell mediated immunity
1. T-cells
2. Attack infected “self” cells
3. Differentiation into several cell types:
A) Cytotoxic T-cells
B) Helper T-cells
C) Suppressor T-cells
D) Memory T-cells
Cytotoxic T-cells
1. Destroy infected “self” cells via secretion of perforin
2. Perforin (perforating) creates holes in the target cell’s membrane
3. Indirectly destroy target cells by inducing apoptosis via the secretion of chemicals
4. The cytotoxic T-cells can only destroy “self” cells, only if those cells present the
foreign antigen on class I MHC (major histocompatibility) proteins (self proteins)
Chapter 39 - The Body Defenses
Helper T-cells
1. Secretion of B-cell growth factor
2. Secretion of T-cell growth factor (Interleukin 2)
3. 60-80% of all circulating T-cells
4. “Commander” cell
Chapter 39 - The Body Defenses
Suppressor T-cells
1. Inhibit the immune response
2. Activated by T-helpers but slow to develop
Memory T-cells
1. Provide rapid mobilization of the immune response if the system is subsequently
exposed to the same antigen
Chapter 39 - The Body Defenses
How is the specific immune response initiated?
1. Foreign antigen must be phagocytized by a macrophage which will present the
antigen “properly” to the lymphocytes (T & B)
2. The macrophage will present the antigen on specific class II MHC receptor proteins,
which are found on the surfaces of special immune cells (B-cells, cytotoxic T-cells, &
macrophages)
3. Binding of the lymphocytes to the presented antigen will activate them
4. B-cells & T-helper cells will recognize the antigen-MHC complex on the
macrophage
5. Activated T-helpers secrete a B-cell growth factor which will stimulate B-cell
differentiation into plasma cells (humoral immunity)
6. Interleukin 1 secreted by the macrophage will also stimulate B-cell differentiation
7. Some B-cells will differentiate into memory B-cells for long term immunity =
important for fast, secondary response (i.e. won’t get sick again)
8. Activated T-helpers secrete T-cell growth factor which activates cytotoxic T-cells
(cell-mediated immunity)
Chapter 39- Blood
Chapter 39- Blood
Chapter 39- Blood
Chapter 39- Blood
Chapter 39 - The Body Defenses
Specific Immunity & Hemolytic disease of the newborn
Rh factor is a surface antigen on RBCs
If mom is Rh negative & gives birth to Rh postive baby = mom will have an immune
response against the Rh antigen = develop antibodies against the Rh antigen & will
attack any subsequent Rh positive baby
Chapter 39- Blood