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Immune
system
• What’s the purpose of receiving a vaccine?
• Why do you think schools require that students be up to date on
their immunizations?
• Aside from vaccines, how might you build immunity to a specific
infectious disease?
• Pathogen: a disease causing agent
• Most pathogens are infectious microbes such as
bacteria or viruses that are capable of causing
disease (many produce toxins).
• Other parasitic organisms such as fungi and some
protozoans are also considered pathogens.
• NOT ALL microbes are harmful, the word pathogen
refers specifically only to microbes that cause
disease.
Salmonella bacteria
• The body has a number of defenses in the immune
system that fight off pathogens
• Some defenses are considered non-specific because
they are not aimed at a specific pathogen
• Help to prevent a disease
• If disease does occur, this helps to slow the spread of the
disease.
• Dead skin cells help protect against invasion by
microorganisms.
• Some bacteria live on our skin symbiotically. They digest oils
produced by the skin and then secrete a mild acid that inhibits
many pathogens.
• Saliva, tears, and mucus contain lysozyme.
• Lysozyme: an enzyme that breaks down bacterial cell walls
killing the bacteria.
• Mucus acts as a protective barrier by blocking bacteria from
sticking to the epithelial cells (cells under the mucus lining).
• If a pathogen gets through the non-specific
barriers there are 3 non-specific responses that
may occur.
Invasion at Normandy, France
• Phagocytosis: Process in which a phagocytic cell
surrounds and internalizes a foreign microorganism.
• Once the pathogen is internalized the phagocyte releases
digestive enzymes and other chemicals from their lysozomes
to destroy the pathogen.
bacterium
phagocyte
• Virus infected cells secrete a protein called interferon.
• Interferon binds to neighboring cells and causes those
cells to produce antiviral proteins so those cells aren’t
infected with the virus.
• Interferon allows cells to communicate to the immune
system to eradicate a pathogen or a tumor.
• Increased blood flow to the infected area makes blood
vessels more permeable to allow white blood cells to
enter the infected area.
• Lymphatic system
• Organs and cells that filter lymph fluid and destroy
pathogens.
• Lymphocytes: a type of white blood cell (WBC)
produced in the bone marrow
• Lymph nodes, tonsils, spleen, thymus gland & other tissues
in mucous membranes in the intestinal, respiratory, urinary,
and genital tracts.
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B-Cells
Helper T-Cells
Killer T-Cells
Memory Cells
• Antigen: A substance on a pathogen that causes the
immune system to produce antibodies.
• Antigens have marker molecules (proteins) on their
surface that have unique shapes making them identifiable
to other cells.
• Antibody: A substance produced by the immune system
in response to (against) an antigen
• An activated helper T-Cell presents processed
antigens (from a pathogen) to a B-Cell.
• B-Cell: manufactures antibodies to bind the antigen
in the body.
• The antibodies enhance immune system response
by binding to pathogens making them more
susceptible to phagocytic destruction and also speed
up inflammation and non-specific response.
• Located in all lymphatic tissues
Antibody Receptor
Antigen Markers
• Helper T-Cells: bind to & activate cytotoxic T-Cells (Killer T
Cells) to help fight a pathogen
• Activated Killer T-Cells: destroy pathogens and release
chemicals called cytokines. Cytokines help to stimulate
the immune system. Especially good at killing virus
infected cells
Pathogen
Killer T-Cell
• Passive Immunity: Temporary protection produced
when antibodies made by other people or animals
are transferred into the body.
• Active Immunity: Long term immunity that occurs after the
immune system has been exposed to disease and memory
cells have been produced.
• This occurs when the immune system is re-exposed
to a particular antigen.
• Faster response compared to the primary exposure
• B and T-Cell response is greater during a secondary
exposure
• The memory of the antigen lasts longer (more memory cells
produced)
• Memory Cells: Remember antigens of pathogens
we have been exposed to in the past so our body
can quickly destroy the pathogen if it enters the
body again.