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AP Bio - Immune System
Transcript of AP Bio - Immune System
The Immune System
The vertebrate immune system is comprised of many different organs and structures.
The major parts in the specific immune response include the
, and the population of
that patrol the circulatory system.
Animals are the only organisms with major immune systems.
All animals possess a degree of
Vertebrates also possess an
immune system that can respond to specific
The external immune system includes barriers like skin, and mucous membranes, and secretions like mucus and sweat.
Skin presents a waterproof barrier to infection.
Sweat glands make the surface of the skin inhospitable to many microorganisms.
There is a population of hundreds of
species of microorganisms that live on the skin and occupy space that pathogens might otherwise occupy.
Mucus is disgusting and sticky for a reason.
Mucus lines all
in the body (which are not as impenetrable as skin).
(as do most other fluid secretions) which disrupts bacterial cell walls.
The epithelial lining of the respiratory track is highly
Together with mucus, this serves as a trap for many pathogens, which are then pushed out of the respiratory tract and into the digestive system.
The Inflammatory Response
Occurs whenever the skin is ruptured, or the body is otherwise infected.
Cells at the site of the infection will release signaling molecules that recruit populations of phagocytic cells to the area.
These signaling molecules will also increase blood flow to the area, which manifests as swelling and redness.
Populations of white blood cells that patrol the circulatory and lymphatic system.
Phagocytize any material that they do not recognize.
Following phagocytosis, pieces of pathogens are presented to the specific immune system for possible specific response.
Internal innate immunity is the responsibility of leukocytes that develop from
myeloid stem cell
precursors (they mature in the bone marrow).
These cells are collectively known as "
Adaptive immunity is the responsibility of leukocytes that congregate in the lymphatic system ("
mature in the bone marrow.
mature in the thymus gland.
B-Cell mediated response.
Results in the production of
, specific to particular molecules on particular pathogens (
Phagocytes will present antigens to Helper T-Cells.
Helper T-cells will activate specific B-cells.
The activated B-cells differentiate into two populations:
- make and secrete antibodies into the circulatory system
- remain viable and circulating in the lymphatic system in case of future infection by the same pathogen.
B-cell receptors and antibodies
2 heavy chains
2 light chains
Both chains have a
The structure of the variable region is specific to a particular antigen
The structure of the antibody gene consists of multiple exons that are randomly combined as B-cells differentiate.
One gene can produce millions of different antibody protein variations.
When a specific antigen is presented to undifferentiated B-cells, they begin to produce different antigen receptors.
Each B-cell that is produced is screened against the antigen. Only B-cells with reactive antigen receptors are allowed to divide ("
Once a B-cell that has an antigen receptor specific for the antigen is produced, it founds a population of plasma cells which secrete plasma antibodies.
Antibodies have 3 major effects on pathogens:
: The pathogen is tagged by the antibody for phagocytosis.
: The antibody prevents the pathogen from infecting more cells.
: The complement system forms pores in the pathogen's cell membranes, which triggers lysis.
After the initial exposure ("
") to a particular antigen, memory cells remain in the body for subsequent exposures ("
") to the same antigen.
T-Cell mediated response.
Results in the activation of particular T-cells, that recognize specific antigens.
T-cell receptors and actions
Phagocytes will present antigens to Helper T-Cells.
Helper T-cells will activate specific T-cells.
The activated T-cells differentiate into two populations:
- find cells that express a particular antigen and trigger the death of those cells.
- remain viable and circulating in the lymphatic system in case of future exposure to the same antigen.
is similar to the B-cell receptor
In order to respond to a particular antigen, a T-cell must interact with a cell that is presenting the antigen complexed with its "
Major Histocompatibility Complex
This is called "
The MHC/Antigen complex is expressed in all phagocytes, cells infected by a particular pathogen, and many cancer cells.
Following recognition, Cytotoxic T-cells will insert a
complex into the membrane of cells that express the MHC/antigen complex, which triggers cell death via lysis or apoptosis
Both the humoral and cell-mediated immune responses rely upon the action of
cells to begin the process.
Together, both responses protect the organism against pathogens, infected cells, and cancer cells.
Immune response to non-pathogenic foreign molecules
Inflammatory response (often in the respiratory system) due to release of histamine.
Antihistamines, epinephrine (for anaphylaxis)
Immune response to populations of body cells
Depends on the nature of the disease
Immunosuppressant drugs (sometimes)
Infection by the HIV virus, which infects Helper T-Cells.
Decrease in Helper T-cell population.
Lack of immune response to "
Antiviral drug therapies.
Palliative care for complications.
Vaccines are a way to expose the immune system to antigens without exposing the body to a functional pathogen.
First discovered by
Arguably the single most important advancement in human health.
Vaccines are powerful, but there are many pathogens that can get around vaccination by shifting the structure of their antigens ("
Evolution always applies!
Receptors present on the surface of phagocytes that respond to molecules found in fungi, bacteria and viruses, but NOT found in animal cells.
Invertebrates possess a series of antimicrobial peptides that activate
and trigger immune responses.
Fungi & Plants
It is thought that restriction enzymes protect prokaryotes from bacteriophage infections.
Fungi and Plants rely on the production of a wide variety of chemicals that can cause unpleasant effects in would-be pathogens and predators.
The "Death Cap" mushroom produces
chemicals that cause irreversible liver failure in humans.
The Penicillium genus of fungi produce
(like penicillin) to protect against bacterial infections.
Plants have systemic mechanisms to prevent the spread of viral infections
The diversity of chemicals that plants can produce in response to pathogens is remarkable!
their own restriction sites, prokaryotes can protect against phage infection.
b. Of course, phages can evolve mechanisms to evade prokaryotic defenses.
Make Sure You Can
What is the purpose of the immune system?
How does the immune system function?
Why do animals have a more developed immune system than other organisms?
Shown: Rheumatoid arthritis, a disease in which the immune system causes inflammation and destruction of connective tissue in the joints of the body.
Explain the structure and function of all parts of the vertebrate immune system.
Describe the interrelationship between innate and acquired immunity.
Explain how B-cells and T-cells function in the acquisition of specific immunity.
Explain the causes, effects, and treatments of immune system disorders.
Describe how a vaccine works (and why it doesn't sometimes).
Explain why animals are the only organisms with extensive immune systems and how other lineages of life deal with immunity.
Clonal Selection is Amazing!
There are 2 kinds of lymphocytes.