Transcript immune_system_lecture

The Human Immune
System
What defenses do our bodies have against
disease?
Immune System Functions
The Immune System helps maintain
homeostatic balance
by fighting pathogens and eliminating
diseased cells,
recycling dead cells, cell debris, and
nutrients.
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Body Defenses Against Disease
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First line of defense
 Physical: cilia in respiratory tract, skin
 Chemical: secretions such as mucus, tears,
and sweat contain lysozyme and other
chemicals that fight germs; stomach acid
Specific and nonspecific defenses –
immune system reactions
Human Immune System
 Lymphatic system
– network of
vessels that
collects, filters, and
returns plasma
that leaks from the
bloodstream.
 Organs and cells
that filter lymph and
blood and destroy
foreign
microorganisms
Immunity – Resistance to Disease
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Passive – comes from outside:
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Antibodies in breast milk  baby
Antibodies produced in animal  human
Immune cell transplant
Active – immune response produced by
the body:
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Antibodies made in response to infection
Cells that kill cancer and virus-infected cells
Passive Immunity – “Borrowing”
antibodies from another human being
Ex.: Colostrum is rich in antibodies,
comes out before mother’s milk
Passive Immunity – “Borrowing”
antibodies from another human being
Ex.: Gamma Globulin - injected antibodies
Antivenom Production
Ex.: antidote against snake venom
Inject Horse, rabbit, or other
animal with venom; animal
antibodies the horse makes
are an
example
produces
antibodies
against of
ACTIVE
___________
immunity.venom.
Milk snake to obtain venom.
The
The antibodies injected into a person to treat snake bite
PASSIVE
are ___________
immunity.
Purify antivenom from
horse serum.
Active Immunity – body makes its
own antibodies, Permanent Protection
Ex.: Immune
reaction
after
exposure to
disease 
some
symptoms
Immune Cells
White blood cells -- leucocytes
 Made in red bone marrow
 found in lymph, blood, and tissues
 Some can migrate to area of infection
 Fight germs specifically and nonspecifically
Bone Marrow Stem Cells
Lymph Cells
B-Cells
T-Cells
Blood Cells
WBC RBC Platelets
Nonspecific Defenses
Effective against many types of pathogens
 Phagocytes engulf and kill many germs (macrophages,
neutrophils)
 Natural killer cells kill virus infected cells
 Interferon – chemical defense against viruses
 Inflammation – histamines increase blood flow, immune
cells migrate to the area
Macrophage
Neutrophil
Inflamatory Response
Specific Immunity
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Effective against a specific pathogen
Pathogens have antigens, usually proteins, that
immune cells identify as foreign
Body has millions of lymphocytes, special
leucocytes with receptors for specific antigens
Lymph nodes – pathogens are identified:
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If a lymphocyte is present that has a receptor for the
antigen on the pathogen, an immune reaction starts
The presence of the specific receptor depends on
having the gene for it.
Lymphocytes & Specific Immune
Responses
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T lymphocytes – T cells, mature in the Thymus
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Helper T cells* – recognize antigens, initiates immune
reaction
Cytotoxic T cells – kill cancer and virus infected cells 
cell-mediated response
B lymphocytes – B cells, mature in the Bone
marrow
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Make antibodies – proteins that bind to antigens – when
activated by a helper T cell
 antibody-mediated or humoral response
* HIV infects and kills helper T cells, stopping many
immune reactions from happening.
Lymphocyte
Production &
Maturation*
+
T cells*
+
B cells*
Antigen
Cytokines
Ex.: interleukins
or CYTOTOXIC T CELL
specific for antigen
is activated & replicates
APC
(Antigen-Presenting Cell,
usually a phagocyte )
digests the pathogen & presents
antigens to a helper T cell
Cytotoxic T and Killer cells
secrete cytotoxins that
Cell Mediated
kill infected body cells
Immune Response
* Most prevalent with intracellular
parasites *
Why?
Must destroy infected cells.
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Antibody (Humoral) Response
* most prevalent with extracellular parasites *
1.
2.
3.
Helper T cells recognize antigens from
pathogens or APC;
Helper T cells activate B cells that have
the proper antibody shape to start
making antibodies;
Antibodies bind to pathogens and mark
them for destruction by phagocytes or
“complement” proteins found in blood.
An Antibody Molecule
B cells have antibodies on
their surface as receptors
for activation.
B cells secrete antibodies
that attach to the antigens
on the pathogen
http://www.cellsalive.com/antibo
dy.htm
Antigen-binding sites 
Opsonization
Antibodies bind to the antigen on the pathogen’s
surface and “tag” the germ for destruction
neutrophils
phagocytosing
Anthrax bacilli
Complement proteins
bind to antibodies
attached to the germ
and cause cell lysis
B & T Cell Activation & Replication
APC
Helper T
More prevalent w/
extracellular pathogens
Activated B Cells replicates &
secrete antibodies that
stick to antigen on pathogen
More prevalent w/
intracellular pathogens
Activated Cytotoxic T Cells replicate &
secrete cytotoxins that kill infected cells
Memory Cells remain after immune
reaction.
Vaccination or
Immunization
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After a specific immune reaction, memory cells may be
left that recognize the pathogen
Vaccination/immunization takes advantage of this:
 A pathogen (killed or attenuated) or an antigen from
it is introduced into the body
 An immune reaction against the antigen happens 
primary response
 Memory cells are quickly reactivated when the real
pathogen infects the host in the future  secondary
response, faster
↓
takes
7-10 days
↓
Much faster:
1-2 days,
Hours?
What do you infer from the graph?
We react differently to different pathogens/diseases 
Some reactions are better than others
Consider that:
1. The ability to make specific antibodies and cell
receptors is genetic.
2. We can make 10 million+ different
antibodies/receptors by shuffling DNA segments in
our genes.
3. Making antibodies/immune cells against our own
antigens  autoimmunity
Disease A
Disease B
Allergies (noninfectious)
Immune system produces antibodies to a
nonpathogenic substance found in the
environment
Plant pollens
Dust
Dust mites
Various foods
Autoimmunity (noninfectious)
 Immune system makes antibodies
to proteins found in the body,
destroying body’s own tissues
Rheumatoid arthritis
Rheumatic fever
Lupus
Multiple Sclerosis
Biotechnology
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Antibodies are used in many biotech
applications; ex.: immunofluorescence
ELISA assay
(Biology Project at U. Arizona)
Immunofluorescence
Antibodies with fluorescent tags can be used to label different proteins in cells.