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Unit 10 notes: The Immune System
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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.
Non-Specific Immunity
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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
o Help to prevent a disease
o If disease does occur, this helps to slow the spread of the disease.
1. Skin Barrier
 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.
2. Chemical Barriers
 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).
Non-Specific Responses to invasion
If a pathogen gets through the non-specific barriers there are 3 non-specific responses that may occur.
3. Cellular Defense
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.
4. Interferon
 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.
5. Inflammatory Response
 Increased blood flow to the infected area makes blood vessels more permeable to allow white blood
cells to enter the infected area.
Unit 10 notes: The Immune System
Name:_________________________________________
Specific Immunity
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.
Four Important Immune Cells
 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
B-Cell Response
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
T-Cell Response
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
Passive Immunity
Passive Immunity: Temporary protection produced when antibodies made by other people or animals
are transferred into the body.
Active Immunity
Active Immunity: Long term immunity that occurs after the immune system has been exposed to
disease and memory cells have been produced.
Unit 10 notes: The Immune System
Name:_________________________________________
Secondary Response To Antigen
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.