Immune System

any change, other than injury, that disrupts the normal functions of the body
may be inherited (ex. hemophilia)
may be caused by materials in the environment (ex. cancer)
may be caused by pathogens (bacteria, viruses, fungi)
3 causes of disease
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(1) bacteria destroy cells or release toxins . (2) protists, fungi, and worms are parasites.
(3) viruses use a host cell to make copies of the viral DNA
diseases are spread through coughing, sneezing, physical contact, contaminated water/food, or infected animals
Agents of disease
1. a carrier, especially the animal (usually an arthropod) that transfers an infective agent from one host to another.
2. a plasmid or viral chromosome into whose genome a fragment of foreign DNA is inserted; used to introduce foreign DNA into a host cell in the cloning of DNA. (e.g. Mosquitoes)

In gene therapy, a virus itself may serve as a vector, if it has been re-engineered and is used to deliver a gene to its target cell. A “vector” in this sense is a vehicle for delivering genetic material such as DNA to a cell.

In genetics more generally, DNA by itself may be regarded as a vector, for example in particular when it is used for cell transformation. A vector in this sense is a DNA construct, such as a plasmid or a bacterial artificial chromosome, that contains an origin of replication.

compounds that kill bacteria without harming the cells of animals by interfering with the cellular processes of the bacteria
injection of weakened or killed pathogens.
when a person receives a vaccine, the body reacts by making protective substances called “antibodies”. The antibodies are the body’s defenders because they help to kill off the germs that enter the body. In other words, vaccines expose people safely to germs, so that they can become protected from a disease but not come down with the disease.
How do vaccinations prevent illnesses?
Specific Defense (it can differentiate between specific microorganisms and respond accordingly)
Nonspecific defense.
What the 2 categories of defense for the Immune system?
things that protect the body from specific pathogens. It includes the third line of defense. They include the lymphocytes (white blood cells) such as the macrophages, t cells, and memory b cells. Macrophages gobble up the bacteria, while t cells actively kill it, and memory b cells remembers the antigen for a faster immune response in case the body is invaded by the specific bacteria again.
Specific defense
things that protect the body from various bacterias, viruses, and pathogens. These include the first and second line of defense, such as the skin, fever( body gets hot as an attempt to kill the pathogen).
Nonspecific defense
The swelling occurs because the blood vessels in the area dilate and become more permeable, allowing those lymphocytes to travel to the site of injury quickly. The inflammation, heat and swelling are nonspecific defenses. The specific defenses are the lymphocytes.
Scenario: You are rock climbing and you fall onto a bunch of rocks gracefully without being injured. Then a ninja comes and stabs you. You notice inflammation, swelling and heating. What is going on and what is nonspecific and what is specific?
A physical barrier like skin is a part of the _____ line of defense.
Is the skin a specific or non-specific defense?
First, take into account the fact that we slough off layers of skin each day! Because we’re able to do this, bacteria have a harder time finding a way in because the cells with the bacteria eventually just get sloughed off.

Another mechanism is the fact that the outter layer of our skin, the epidermis, is very dry. And you know, in order for life to sustain itself you need water. Our skin is dry on purpose, to prevent the growth of bacteria – who love warm, moist envirnoments! (i.e. like the inside of us!)

Beneficial bacteria that live on the skin provides protection by releasing acids and wastes to kill off unwanted microorganisms. (Chemical)

The layer of overlapping dead cells on the surface of the skin prevents pathogens from entering the body. A break in the skin gives pathogens access to body tissues. If this happens blood clots then form a temporary barrier until new skin seals the wound.

Name 4 chemical or physical ways that the skin functions to protect the body from pathogens.
a bacterium, virus, or other microorganism that can cause disease.
a toxin or other foreign substance that induces an immune response in the body, especially the production of antibodies.
A pathogen is any organism capable of producing disease.

An antigen refers to the protein on the surface of a cell (bacterium, fungus or virus) that our bodies recognize as a foreign substance and triggers the immune system into producing antibodies specific to that antigen. This means that if in the future the same antigen is again introduced, our immune system will recognize, remember and produce the right antibodies to “deal” with the intruders.

Difference between pathogens and antigens
(1) First line of defense. Non-specific barriers.

(2) Second line of defense- Leucocytes (white blood cells)

(3) Third line of defense – specific immune response

What are the three lines of defense?
These are a combination of physical and chemical barriers that prevent all types of foreign agents from penetrating the outer layer of the body.
First line of defense
(1) The skin – provides an impervious barrier to pathogens.

(2) Mucous membranes – line the entrances to the body such as in the respiratory tract entrances. Mucus produced by these membranes traps foreign particles and directs them out of the body.

(3) Hairs and cilia – (nasal hairs) trap dust and dirt; (microscopic cilia) line some mucous membranes and direct foreign particles out of the body.

(4) Gastric juice, vaginal secretions and urine – acidic fluids that have a protective function.

(5) Tears, sweat and saliva – body fluids which possess some anti-bacterial properties.

(6) Cerumen (ear wax) – produced in the ear canal and protects the canal by trapping dirt and dust particles.

Examples of the First line of defense
found circulating throughout the body and if a pathogen penetrates the first line of defence, these cells play a role in inhibiting or destroying the pathogen before it harms the body. They are non-specific opens in a new window and react to the presence of any foreign organism or substance. There are two main types of leucocytes: granulocytes opens in a new window and agranulocytes opens in a new window.
Second line of defense – leucocytes (WBC)
If a foreign agent penetrates the non-specific barriers, there is a third line of defence available – the specific immune response.

The specific immune response is a mechanism that is activated by the presence of pathogens and foreign substances. These are known as antigens. Even transplanted tissue from another person, or parts of pathogens like the flagella of a bacterium, are recognised as antigens.

The body’s immune system can determine which antigens are part of its own body structure. These antigens are known as self-antigens opens in a new window. These do not stimulate an immune response.

Non-self antigens opens in a new window are the foreign substances that do stimulate an immune response.

The presence of a non-self antigen can trigger the production of specific proteins called antibodies opens in a new window. These are special proteins that are secreted by specific lymphocytes and have a specific molecular shape that matches the molecular shape of an antigen. The shape of the antibody gives it the ability to combine with and inactivate the antigen. When an antibody combines with an antigen the result is an antigen-antibody complex.

Third line of defense – specific immune response
The inflammatory response is part of the ______ line of defense.
Is inflammation specific or non-specific?
Inflammation happens because cells damaged by invading pathogens and particular white blood cells release ‘alarm’ chemicals which makes blood vessels enlarge (vasodilate) and the capillaries more ‘leaky’.

This means that:

More blood is coming to the site of the infection, bringing with it more white blood cells of the immune system
2. Then, the white blood cells are let out of the blood capillaries and into the affected tissue.

This extra blood makes the area red (as more blood means that the area looks red) and swollen (more blood and liquid leaving the blood and entering the tissue fluid surrounding the body cells).

The area will also become hot (as the extra blood is also carrying heat with it) and painful (because the tissues will be swollen with the blood).

Inflammation also attracts white blood cells to the area.

How does inflammation protect the body when the skin is cut? (important)
B-cells are part of the third line of defense, which is specific.
B-cells are part of what line of defense?
Even though most B cells (and T cells) reside in the spleen, B cells mature in the bone marrow. Once the B cell is activated, the b cell can go to the germinal centre within the spleen where they undergo somatic hypermutation and can switch their antibody production to that of a different class.
Where do B cells mature?
T cells mature in the thymus.
Where do T cells mature?
Just think B-cells = bone marrow
T-cells = Thymus
Trick to remember where B cells and T cells mature:
(1) Plasma B cells are large B cells that have been exposed to antigen and are producing large amounts of antibodies, which assist in the destruction of microbes by binding to them and making them easier targets for phagocytes.

(2) Memory B cells are formed from activated B cells that are specific to the antigen encountered during the primary immune response. These cells are able to live for a long time, and can respond quickly following a second exposure to the same antigen.

(3) There are also two other B cells, B-1 cells and B-2 cells. read more @

What are two types of B cells and what do they do?
antigens and pathogens
What do T cells defend against?
(1) Cytotoxic T cells
(2) Helper T cells
(3) Memory T cells
What are the three major types of T cells?
secrete cytotoxin which triggers destruction of the pathogen’s DNA or perforin which is a protein that creates holes in the pathogens plasma membrane. The holes cause the pathogen to lyse (rupture).
Cytotoxic T cells
These cells secrete interleukin 2 (I-2) which stimulates cell division of T cells and B cells. In other words, these cells recruit even more cells to help fight the pathogen.
Helper T cells
These cells remain dormant after the initial exposure to an antigen. If the same antigen presents itself again, even if it is years later, the memory cells are stimulated to convert themselves into cytotoxic T cells and help fight the pathogen.
Memory T cells
primary immune response refers to the first encounter of your immune system with a virus or bacteria. when this happens, naive T cells and B cells are activated and form memory cells. This process takes a week or so, which allows you to get sick and not feel well, but these cells eventually clear the pathogen from your body.

a secondary immune response refers to a re-encounter of the same virus/bacteria against which you have memory T cells and B cells. since the memory cells have seen the bug before, they can respond very rapdily and robustly, preventing you from feeling sick.

Describe the primary and secondary response to the same antigen.
1. Scavenge dead, dying body cells
2. Destroy abnormal (cancerous)
3. Protect from pathogens & foreign molecules: parasites, bacteria, viruses
3 Immune System Functions
1. Physical and Chemical Barriers (Innate Immunity)

2. Nonspecific Resistance (Innate Immunity)

3. Specific Resistance (Acquired Immunity)

The Immune System has 3 lines of defense against foreign pathogens
Y-shaped proteins that circulate through the blood stream and bind to specific antigens, thereby attacking microbes.

The antibodies are transported through the blood and the lymph to the pathogen invasion site.

The body contains millions of different B cells, each able to respond to one specific antigen.

(1) Lysozyme, an enzyme produced in tears, perspiration, and saliva can break down cell walls and thus acts as an antibiotic (kills bacteria)
(2) Gastric juice in the stomach destroys bacteria and most toxins because the gastric juice is highly acidic (pH 2-3)
(3) Saliva dilutes the number of microorganisms and washes the teeth and mouth
(4) Acidity on skin inhibit bacterial growth
(5) Sebum (unsaturated fatty acids) provides a protective film on the skin and inhibits growth
(6) Hyaluronic acid is a gelatinous substance that slows the spread of noxious agents
Chemical barriers (innate immunity)
The second line of defense is nonspecific resistance that destroys invaders in a generalized way without targeting specific individuals:
(1) Phagocytic cells ingest and destroy all microbes that pass into body tissues.
(2) Inflammation brings more white blood cells to the site where the microbes have invaded. The inflammatory response produces swelling, redness, heat, pain
(3) Fever inhibits bacterial growth and increases the rate of tissue repair during an infection
Nonspecific Resistance (Innate Immunity)
The third line of defense is specific resistance. This system relies on antigens, which are specific substances found in foreign microbes.

Most antigens are proteins that serve as the stimulus to produce an immune response. The term “antigen” comes from ANTI-body GENerating substances.

Here are the steps in an immune response:

When an antigen is detected by a macrophage (as describe above under phagocytosis), this causes the T-cells to become activated.
The activation of T-cells by a specific antigen is called cell-mediated immunity. The body contains millions of different T-cells, each able to respond to one specific antigen.

The T-cells secrete interleukin 2. Interleukin 2 causes the proliferation of certain cytotoxic T cells and B cells.
From here, the immune response follows 2 paths: one path uses cytotoxic T cells and the other uses B cells.

Specific Resistance (Acquired Immunity)
1. Neutralizing an antigen – The antibody can bind to an antigen, forming an antigen-antibody complex. This forms a shield around the antigen, preventing its normal function. This is how toxins from bacteria can be neutralized or how a cell can prevent a viral antigen from binding to a body cell thereby preventing infection.
2. Activating complement – Complement is a group of plasma proteins made by the liver that normally are inactive in the body. An antigen-antibody complex triggers a series of reactions that activates these proteins. Some of the activated proteins can cluster together to form a pore or channel that inserts into a microbe’s plasma membrane.This lyses (ruptures) the cell. Other complement proteins can cause chemotaxis and inflammation, both of which increase the number of white blood cells at the site of invasion.
3. Precipitating antigens – Sometimes the antibodies can bind to the same free antigen to cross-link them. This causes the antigen to precipitate out of solution, making it easier for phagocytic cells to ingest them by phagocytosis (as describe above).

Also, the antigens within the cells walls of the bacteria can cross-link, causes the bacteria to clump together in a process called agglutination, again making it easier for phagocytic cells to ingest them by phagocytosis.

4. Facilitating phagocytosis – The antigen-antibody complex signals phagocytic cells to attack. The complex also binds to the surface of macrophages to further facilitate phagocytosis.

Four ways antibodies work

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