Transcript immune system 2010

THE IMMUNE SYSTEM
Populations & Ecosystems
2011
• Pathogens can enter the body via:
• Inhalation
• Wounds in the skin
• Through mucous membranes (moist surfaces);
trachea, urinary tract, vagina, digestive tract
• Body fluids; blood transfusion, seminal fluid,
saliva, breastmilk
• Transplanted organs
• We need protection from pathogens, or
we would quickly die from infections.
• “The boy in the bubble”- there is a rare
genetic disease where the immune
system doesn’t develop. Unless
protected from pathogens, patients die
within a few months.
• The most famous case was David Vetter
(1971-1984).
• He spent his entire life in an enclosed
room, until he received a bone marrow
transplant from his sister. He died soon
after from the effects of a virus that he
received in the bone marrow from his
sister.
The immune system
• Innate (nonspecific) immunity
• Anatomic Barriers
• Physiological Barriers
• Phagocytic Barriers
• Inflammatory Barriers
• Adaptive (specific) immunity
• Humoral Immunity - B cells and Antibodies
• Cellular Immunity - T cells
• Clonal Selection Theory
Innate immunity (non-specific)
• Not specific to a particular pathogen
• First barriers to an invading pathogen
• Controls most infections
Skin
• Skin
• Physical barrier
• 3 layers
• outer layer (epidermis) made up largely of the
structural protein keratin
• waterproof and barrier to infection
• Oil & sweat give the skin a pH of 3-5
• Lysozyme (enzyme also found in tears)
destroys bacteria
• Mucous membranes-
respiratory, urogenital &
gastrointestinal tracts
(wet surfaces)
• Trachea has lining
(epithelial) cells
• Mucous catches
foreign material
• Fine beating cilia
move the layer of
mucous up away from
the lungs
• Vagina and urinary
tract are acidic
Phagocytic barrier
• Phagocytes engulf and
destroy pathogens
• Macrophages,
neutrophils, monocytes,
eosinophils
Physiological barriers
• Temperature
• Raised body temperature inhibits some
pathogens
• Low pH (e.g. stomach)
• Chemical mediators
• lysozymes in tears, sweat and mucous digests
cell walls of many bacteria
Inflammatory response
• Chemicals (particularly histamine) are released
from injured areas
• Attract white blood cells
• Cause vasodilation
• Increase permeability of blood vessels
• Redness, swelling, heat
• Pain
• Complement system
• Consists of special
proteins circulating in the
blood
• When activated, the
proteins make a hole in
bacterial cell membranes
• Fluid rushes into the
bacteria & they explode!
Adaptive immunity
• The body responds to specific pathogens
• Cell mediated immunity: phagocytic
lymphocytes ‘eat’ pathogens
• Humoral immunity: lymphocytes produce
antibodies
Lymphocytes
• Found in:
• Blood
• 20-40% of white
blood cells
• Lymphatic tissues
• Tonsils, lymph nodes,
spleen
• There are several types of lymphocytes:
• B cells (B lymphocytes)
- activated to become plasma cells
- secrete antibodies
• T cells (T lymphocytes)
- TH cells - CD4+, cytokine secreting
- TC cells - CD8+, cytotoxic (killer) cells
Antigens
• Antigens are proteins or carbohydrates which are
foreign to the body
• Antigens are found on the surface of bacteria, viruses,
transplanted cells etc…
• Anything that stimulates production of antibodies is an
antigen
• Antibodies are
proteins with binding
sites which stick to
specific antigens
• Ab’s surround
foreign materials &
inactivate them
• Then the antibodyantigen complexes
can be
phagocytosed
Antibodies:
• Neutralisation
• Agglutination
• Opsinisation
• Antibodies bind to bacteria,
enhancing phagocytosis
• Activate complement
system
T lymphocytes
• T lymphocytes respond to antigens that are
presented to them by macrophages
• Develop into four cell types:
Helper T cells- detect infection, initiate cytotoxic
T cells & B cell response
Cytotoxic T cells- destroy virus-infected cells &
cancer cells
Suppressor T cells- inhibit T & B cells to
dampen response when pathogen is gone
Delayed hypersensitivity T cell- causes
transplant rejection & inflammation in allergic
reactions
B lymphocytes
• B cells recognise and bind to antigens
• Develop into two cell types:
Plasma cells- produce antibodies specific
to an antigen
Memory cells- long-lived cells which
recognise antigens and quickly multiply to
produce plasma cells
Antigens are detected by macrophages and
presented to helper T cells.
2. Helper T cells recognise the antigens as foreign.
a) They stimulate B cells (plasma cells) to produce
antibodies.
b) They also stimulate killer T cells and
macrophages.
3. Afterwards, some B cells remain as memory cells.
4. If the antigen is presented to them again, they
produce plasma cells.
5. The plasma cells produce antibodies very quickly.
1.
HIV/AIDS
• HIV infects the helper T cells (CD4+ cells) and
destroys them.
• This means that the immune system can’t
recognise antigens and respond to them.
• Patients develop secondary infections- bacterial,
viral and fungal diseases (AIDS- acquired
immune deficiency disease)
Clonal selection theory
• Lymphocytes recognise foreign antigens
• But only one antigen is recognised by each
lymphocyte
• Once one lymphocyte is activated, it multiplies into
cloned cells which all recognise the antigen (clonal
expansion)
• Memory cells are ready to multiply rapidly if
exposed to the antigen again
• Lymphocytes that recognise self-antigens are
removed
• Active immunity= body actively producing Ab
• Passive immunity= Ab from an external
source
• Antibodies in breast milk
• Antiserum given after exposure to snake
venom
• Natural immunity= due to natural exposure
• Artificial immunity= due to immunisation
Immunisation
•
The subject is exposed to
an attenuated (weakened)
or killed version of the
bacteria or virus, or from
the viral protein coat.
• The body produces Ab &
memory cells (primary
response)
• If exposed again later,
memory cells detect the
antigen & Ab production
occurs very rapidly
(secondary response)
Current immunisations
• Include (but not limited to):
• Diphtheria
• Whooping cough (pertussis)
• Tetanus
• Measles
• Polio
• Rubella
• Hepatitis A & B
Benefits
Dangers
Some diseases can be completely
eradicated e.g. smallpox
Immunity may only last for several
years, requiring booster shots
Death & long term disabilities
caused by disease are decreased
e.g. prevention of disabilities
caused by prenatal rubella
Herd immunity may cause
complacence  less immunisation
& the disease can re-emerge
Financial benefits due to less time
lost due to illness
Some vaccines may cause side
effects
Herd immunity- if >90% of the
population are immune disease
can’t spread between people
If attenuated live vaccines are
used, the possibility exists for the
organisms to mutate & cause
disease again
Autoimmune diseases
• In autoimmune diseases, the body’s immune
system fails to recognise parts of the body and
attacks them.
• Rheumatoid arthritis
• Juvenile (type I) diabetes (the immune system
destroys the beta cells in the pancreas that
produce insulin)
• Multiple sclerosis