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The Immune System

Image Credits: Biology (Campbell) 9th edition, copyright Pearson 2011, & The Internet,Content derived from David Knuffke,Provided under the terms of a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.Thomas Hattori.
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Thomas Hattori

on 11 February 2016

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Transcript of The Immune System

The Immune System
Innate Immunity
Adaptive Immunity
Humoral
Cell-Mediated
External
Internal
Immune Disorders
The vertebrate immune system is comprised of many different organs and structures.

The major parts in the specific immune response include the
lymphatic system
, and the population of
leukocytes
that patrol the circulatory system.
Animals are the only organisms with major immune systems.
All animals possess a degree of
innate
immunity.

Vertebrates also posses an
adaptive
immune system that can respond to specific
pathogens
.
The external immune system includes barriers like skin, and mucous membranes, and secretions like mucus and sweat.
Skin
Skin presents a water-proof barrier to infection.

Sweat glands make the surface of the skin salty and inhospitable to bacteria.

There is a population of hundreds of species of microorganisms that live on the skin and occupy space that pathogens might otherwise occupy.
Mucus
Mucus is disgusting and sticky for a reason.

Mucus lines all
mucous membranes
in the body (which are not as impenetrable as skin).

Mucus contains
lysozyme
and
defensins
which disrupts bacterial cell walls.
Ciliated Epithelium
The epithelial lining of the respiratory track is highly
ciliated
.

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 (including histamine) will also increase blood flow to the area, which manifests as swelling and redness.
Phagocytes
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 "
phagocytes
"
"non-specific"
"specific"
Adaptive immunity is the responsibility of leukocytes that congregate in the lymphatic system ("
lymphocytes
")

There are 2 kinds of lymphocytes.
B-cells
:
mature in the bone marrow.
responsible for
humoral
(antibody) response

T-cells
:
mature in the thymus gland.
responsible for
cell-mediated
response
B-Cell mediated response.
Results in the production of
antibodies
, specific to particular molecules on particular pathogens (
antigens
)
Phagocytes will present antigens to Helper T-Cells.
Helper T-cells will activate specific B-cells.
The activated B-cells differentiate into two populations:
Plasma cells
- make and secrete antibodies into the circulatory system
Memory cells
- remain viable and circulating in the lymphatic system in case of future infection by the same pathogen.
B-cell receptors and antibodies
Structurally similar.
Consist of
2 heavy chains
and
2 light chains
.
Both chains have a
constant region
and a
variable region
.
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.
Each B-cell is tested to ensure it will not react with the bodies cells ("
clonal deletion
"). Only when a B-cell encounters its specific antigen will it divide ("
clonal selection
").
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:
Opsonization
: The pathogen is tagged by the antibody for phagocytosis.
Neutralization
: The antibody prevents the pathogen from infecting more cells.
Complement activation
: The complement system forms pores in the pathogen's cell membranes, which triggers lysis.
After the initial exposure ("
primary response
") to a particular antigen, memory cells remain in the body for subsequent exposures ("
secondary response
") 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:
Cytotoxic T-cells
- find cells that express a particular antigen and trigger the death of those cells.

Memory cells
- remain viable and circulating in the lymphatic system in case of future exposure to the same antigen.
The
T-cell receptor
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
" (
MHC
) protein.

This is called "
antigen presentation
".

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
perforin
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
Helper-T
cells to begin the process.

Together, both responses protect the organism against pathogens, infected cells, and cancer cells.
Allergies
Autoimmune Diseases
AIDS
Cause
Symptoms
Treatment
Cause
Symptoms
Treatment
Cause
Symptoms
Treatment
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
Immunosuppresant drugs (sometimes)
Infection by the HIV virus, which infects Helper T-Cells.
Decrease in Helper T-cell population.
Lack of immune response to "
opportunistic infections
".
Antiviral drug therapies.
Vaccination
Vaccines are a way to expose the immune system to antigens without exposing the body to a functional pathogen.
First discovered by
Edward Jenner
for smallpox.
Arguably the single most important advancement in human health.
Unfortunately
Vaccines are powerful, but there are many pathogens that can get around vaccination by shifting the structure of their antigens ("
antigenic shift
").
Shown: Rheumatoid arthritis, a disease in which the immune system causes inflammation and destruction of connective tissue in the joints of the body.
Regulatory T cells ("
Tregs
") control the immune system response. Instead of recognizing foreign antigens, they bind to self antigens and inhibit T cells that share the same antigen receptor.
"Acquired Immune Deficiency Syndrome"
Even more unfortunately...
So what if I put my child at risk?
Full transcript