chapter 24 the immune system pathogens disease causing agents such as bacteria, viruses, fungi,...
TRANSCRIPT
Pathogens
• Disease causing agents such as bacteria, viruses, fungi, protozoans, and other parasites. ( NOT all microorganisms are pathogens)
Transmission of disease• Pathogens can be
transmitted to a host from reservoirs in four main ways: by direct contact, by an object, through the air, or by an intermediate organism called a vector.
Immune System
• Bodies primary defense against pathogens• Three cooperative lines of defense have evolved to
counter these threats.– Two of these are nonspecific - that is, they do not
distinguish one infectious agent from another.
1st line: Physical Barriers• non-specific defense• external barriers– skin & mucus membranes– excretions
• sweat • stomach acid • tears• mucus • saliva
– “lick your wounds”
Lining of trachea: ciliated cells & mucus secreting cells
2nd: Generalist, broad range patrols • Patrolling white blood cells– attack invaders that get through the skin• recognize invader by reading antigen
– surface name tag
– phagocyte cells• macrophages• “big eaters”
Macrophage “eating” bacteria
Lymph system Production of white blood cells & traps “foreign” invaders
2nd “circulatory” system lymph node
lymph vessels(intertwined amongst blood vessels)
The lymphatic system becomes a crucial battleground during infection
• a network of lymphatic vessels and organs– It returns tissue fluid to the
circulatory system– It fights infections
• Lymph nodes are key sites for fighting infection– They are packed with
lymphocytes and macrophages
Phagocytes
• Macrophages wander in the interstitial fluid– They “eat” any bacteria
and virus-infected cells they encounter
Antimicrobial Proteins
• Interferons: acts in warning other cells of a viral invasion
• Complement: help attract phagocytes to foreign cells and help destroy foreign cells
Natural Killer cells
• A type of white blood cell that destroy the body's own infected cells, may attack cells that form tumors
The inflammatory response mobilizes nonspecific defense forces
• Tissue damage triggers the inflammatory response (redness, swelling, warmth, pus) injured cells release chemical signals
• histamines– increases blood flow– brings more white blood cells to fight bacteria– brings more red blood cells & clotting factors to repair
• The inflammatory response can– disinfect tissues– limit further infection
Fever
• When a local response is not enough– full body response to infection– raises body temperature – higher temperature helps in defense• slows growth of germs• helps macrophages• speeds up repair of tissues
SPECIFIC IMMUNITY~ 3rd line of defense
• IMMUNE RESPONSE a recognition system that distinguishes “self”
from “non-self”• responds to foreign molecules called antigens• Stimulates the body to make antibodies: specific defensive proteins which help to
counter antigens in various ways
How are invaders recognized?• Antigens– chemical name tags on the surface of
every cell• “self” vs. “invader”
disease-causingbacteria
disease-causingvirus
one of yourown cells
antigens say:“I belong here”
antigens say:“I am an invader”
antigens say:“I am an invader”
Immunity=protection afforded to an organism by previous exposure to an antigen
• 2 types:1. Active: long term, conferred
by actual encounter with infection (naturally acquired) or vaccination *(artificially acquired)
* vaccine~ substance consisting of weakened, dead, ,or parts of pathogen or antigen that when injected , stimulates the immune system
Immunity
2. Passive: short term, antibodies passed on, not stimulated by antigens,
acquired naturally by placenta or breast milk or artificially acquired by a shot
Immune Response ~ 3rd line of defense
• Governed by 2 different parts of the immune system
• 1. Humoral Immunity: results in the production of antibodies
• 2. Cell-mediated Immunity: defensive activities are carried out by specialized cells circulating around the body
Lymphocytes ~type of white blood cell that carry out the immune response
• Two kinds– B cells secrete antibodies
that attack antigens (humoral immunity)
– T cells attack cells infected with pathogens (cell-mediated immunity)
B lymphocyte
The initial immune response results in a type of “memory”
• primary immune response produces memory cells– These cells may confer lifelong immunityWhen memory cells are activated by subsequent exposure to an antigen,
they mount a more rapid and massive secondary immune response
Humoral Immune Response
• Triggered by a specific antigen, a B cell differentiates into a plasma cell
-The plasma cell secretes antibodies
Antibodies are the weapons of humoral immunity
• An antibody molecule has antigen-binding sites specific to the antigen
• Do not posses the power to destroy antigens directly, tag and mark them for destruction by a variety of mechanisms
B cells & antibodies• B cells– white blood cells that attack
invaders in blood– mature in Bone marrow
• Patrolling B cells – make antibodies against invader immediately
• Memory B cells– remembers invader– can make antibodies quickly the next time• protects you from getting disease more than once
B cells immune responseinvader(foreign antigen)
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“reserves”
memory B cells
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B cellsrelease antibodiespatrol bloodforever
recognition
10 to 17 days
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2006-2007
What if the attacker gets past the B cells in the blood &
infects some of your cells?You need trained assassins to kill
off these infected cells!
T
Attackof the Killer T cells!
T cells• T cells mature in Thymus• Helper T cells – sound the alarm for rest
of immune system
• Cytoxic or Killer T cells– destroy infected body cells
• Memory T cells– remembers invader & reacts against
it again quicklyWhere’s that?
Cell-Mediated Immunity• An antigen-presenting cell (APC) first displays a
foreign antigen and one of the body’s own self proteins to a helper T cell
• The helper T cell’s receptors recognize the self-nonself complexes on the APC
- The interaction activates the helper T cells– The helper T cell can then activate cytotoxic T cells with
the same receptors– Helper T cells also stimulate the humoral responses
• Cytotoxic T cells( or Killer T cells) bind to infected body cells and destroy them
Attack of the Killer T cells• Killer T cells destroy infected body cells– T cell binds to invaded cell– secretes perforating protein• punctures cell membrane of infected cell• cell bursts
Perforin puncturescell membrane
cell membrane
Killer T cell
cell membrane
invaded cell
vesicle
Cytotoxic T cells (Killer T) may help prevent cancer
– The surface molecules of cancer cells are altered by the disease
Immune responseinvader
invaders in blood invaders infect cells
B cells T cells
macrophages
helperT cells
patrollingB cells
memoryB cells
memoryT cells
killerT cells
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skinskininvaders in body
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The immune system depends on our molecular fingerprints
– “Self” is signaled by major histocompatibility complex (MHC), a group of proteins unique to the individual that is present on the surface of cells
• Can cause rejection of transplanted organs
DISORDERS OF THE IMMUNE SYSTEM
• Autoimmune diseases– The system turns against
the body’s own molecules
– Examples: Rheumatic fever, Type I Diabetes, Multiple Sclerosis, Rheumatoid arthritis, Lupus
Rheumatoid arthritisRheumatoid arthritis
DISORDERS OF THE IMMUNE SYSTEM
• Immunodeficiency diseases– Immune components
are lacking, and infections recur
Ex: Acquired immune deficiency syndrome (AIDS)
SCIDS
HIV on a lymphocyte
AIDS
– HIV (Human Immunodeficiency Virus) the virus that causes AIDS
– HIV is transmitted mainly in blood and semen
– HIV kills helper T-cells and leads to AIDS
DISORDERS OF THE IMMUNE SYSTEM
• Allergies are overreactions to certain environmental antigens called
allergens : Ex. Animal dander, dust mites, pollen
release of histamine causes symptoms
Antihistamines can relieve symptoms
anaphylactic shock: life threatening reaction to injected or ingested allergens..