Download Immune System

Immune System
 Innate Immune response = fast response to wide range of
microbes; born with.
 Acquired/Adaptive response = slower response to specific
microbes; develops over time due to exposure.
- Only found in vertebrates
 Antigen = protein or glycoprotein on cell surface of “invader”
that stimulates a response by the immune system via leukocytes
(WBC)
o Epitope = specific area on antigens surface receptors
where (our) defense mechanisms will attach.
Antigen may be:
- may be a pathogen = microbe
- or, may cause allergic reaction
 Leukocytes (WBCs) destroy “invader” by phagocytosis or
chemically.
 Attach to microbe via cell surface receptors
- Generalized by groups of different antigens [innate]
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 Vesicle (of WBC) fuses with lysosome = chemicals/enzymes
for destruction of antigen.
 5 types of leukocytes (WBCs)
1. Neutrophils
- targets bacteria & fungi (by phagocytosis)
- usually self-destructive = short lived (live only a few days)
2. Eosinophils
- chemical release for targeting large parasites (not
phagocytosis)
3. Basophils
- Release histamine for inflammatory response
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4. Monocytes
- Produces interferon (protein) for:
1. Tells infected cells and neighboring uninfected cells produce this chemical to limit spread of virus.
o complement system (not phagocytosis)
2. Other interferons help stimulate production of….
******MACROPHAGES (“BIG EATERS”) = tissue resident
(lymph nodes, spleen, tonsils, adenoids, appendix); body’s
primary phagocytes
 Acquired response achieved by…
5. *****LYMPHOCYTE (T-CELLS & B-CELLS)
 Originate from stem cells in the bone marrow…
- T-cells (mature in Thymus gland); clonal
1. Helper T-cells: produces proteins called cytokines to
activate:
a. B-cell to make antibodies (stay in Bone marrow to
mature); clonal
- Helps macrophage find the antigen.
b.
Cytotoxic T-cells - (killer T-cells) – eliminates
body’s infected cells (microbes/cancer) by enzymes
and/or chemicals that will cause leakage of target
cells by creating pores in the cell membrane; clonal
c.
Suppressor T-cells - shuts down immune responses
after they have successfully eliminated invading
organisms; also prevents autoimmunity
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Autoimmunity = when the body’s immune system attacks
itself
o Produces antibodies against healthy body cells if
suppressor cells cannot shut down response to antigen
after infection is cleared.
2. Memory T-cells (both Helper and Cytotoxic) - can
reproduce a faster and stronger immune response than
the first time the immune system responded to the
invader; clonal
- Secondary response
More about B-cells…
- B-Cells (mature in Bone marrow) = creates antibodies
1. Plasma cells – clonal B-cells; secretes antibodies
 1st exposure - short lived effectors
 2nd exposure - more produced = longer lived effect
Due to….
2. Memory B-cells – same function as memory T-cells - faster response to infection after 1st exposure: clonal
Let’s get attacked…
Two kinds of defense: (1. Innate & 2. Acquired Immunity)
1. Innate response
 Non-specific = effective at birth
- Responds to wide range of microbes
 Examples of physical barriers: skin, mucous
membranes, internal chemical defenses
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- Skin
 Sweat and oil gland decrease pH = not
inhabitable by microbes
 Secretions = lysozymes (enzymes)
- Kill microbes; degrade microbial
components
- Mucous membranes
 Tears, saliva = also contain lysozymes
 Stomach = HCl and mucous
If microbe breaks innate physical barriers, chemical
barriers kick in…
 Inflammatory response
- In Mast Cells of connective tissue & basophils
release histamine = dilation & greater
permeability of nearby capillaries
- Increases blood flow to injured cells
- Capillaries engorge
- Leak into tissues = swelling & heat
- Deliver antimicrobial proteins (interferon) and
clotting factors made by monocytes.
• Limits the spread of infection
- Increase WBC’s (phagocytes) killing compounds.
• Neutrophils for bacteria and parasites
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• Monocytes, specifically macrophages, for
viruses
If the innate immune response doesn’t work entirely,…
- Some background first:
2. Acquired (adaptive) response
 First time body is attacked by new antigen =
primary immune response
- Slow = 10 to 20 days after exposure
 Specific = after initial exposure to
antigen/abnormal body cells = secondary response
- Distinguishes one microbe from another
Two forms of Acquired response: achieved by
lymphocytes
 B-cells
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- Humoral defense (in the fluid of the body;
blood, lymph, interstitial fluid) = production
of antibodies by (B-cells)
 Antibodies = proteins secreted by B-cells
that bind to a specific antigen for
elimination.
 T-cells
- Cell mediated defense = cell to cell contact;
cytotoxic T-cells destroy already infected
body cells
OK, let’s continue with the attack…A pathogen bypasses
the body's innate physical/chemical barriers…
inflammatory response did not do the job…
(innate to acquired)
Monocytes (innate)
 macrophages: initiate attack
- nonspecifically engulf invaders [innate]
- incorporate antigens into own membrane
- “presents” to helper T-cells = activation
 results in fever
• compliment system = interferon does its job
preventing spreading of infection
Lymphocytes (connection of innate to acquired)
 helper T cells: initiation of cell–mediated response
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- produces cytokines
- cytokines stimulate production of:
1. B-cells: initiate humoral response
- produce antibodies specific to antigen to
neutralize antigen so macrophage can “eat
antigen”
2. cytotoxic T-cells (killer T-cells) destroy already
infected cells: cell mediated
At the end of infection:
 suppressor T cells:
- multiply slowly
- shuts down antibody response after few weeks;
limits production of:
a.
b.
c.
helper T-cells that activate
B-cells to make antibodies
Cytotoxic T-Cells to stop destruction of
body’s cells.
 *Memory: some T cells and B cells are cloned and
remain circulating
- provides accelerated response to reinfection =
secondary immune response (2 to 7 days)
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Let’s look at antibodies a little closer…
 Antibodies are (glycol-)proteins belong to a group of
molecules = immunoglobulins
 Secreted by B-cells
- Considered soluble when released from B-cells
into the blood and tissue fluids surveying for
microbes
 Antibodies have the same general “Y” shape.
 2 regions to antibody
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1. Getting the antibody delivered to the correct
location in the body and disposal of antigen =
tail end of the “Y”
- This is region establishes 5 classes of
antibodies
- These classes perform different roles
and help direct the appropriate immune
response for each antigen they encounter
2. Specific antigen-binding site = how antibodies
recognize specific antigens (the top of the “Y”)
- variable region = antigen specific
- 100,000’s of different varieties in this region is due
to splicing together different exons of the same
gene.
- random mutations in this area of the antibody gene,
which create further diversity
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Antibodies:
 Leads to destruction by
1. Neutralization – coats pathogen with toxins = blocks
binding sites
2. Agglutination – clumps pathogen where they can be
phagocytized by macrophages
3. Lysis – activation of (different) complement system;
results in the lysis of microbes
 Vaccines – inactive bacterial toxin, killed microbes, parts
of microbes, viable but weak microbes
- Injection stimulates immune response
- Make memory cells
- Quick secondary response if exposed to pathogen
See page 915 and Fig 43.1 – blood groups and
transfusions
 Antigens on the surface of blood cells
- A blood = A antigen
- B blood = B antigen
- AB blood = A & B antigens
- O blood = no antigens
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 The body does not produce antibodies against these
antigens = self-tolerant
 “Self and Non-self”
- Antibodies to foreign blood groups are innately
present for certain blood groups; even though the
body hasn’t been exposed to the foreign blood
group
- A blood = antibodies for B blood antigen
- B blood = antibodies for A blood antigen
- AB blood = NO antibodies for either A or B
blood
Universal acceptor
- O blood = antibodies for both A and B blood
Universal donor
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Universal acceptor
Universal donor
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