Biology 2201

IMMUNE SYSTEM

The ability of the body to fight infection by producing antibodies or cells that deactivate foreign substances.

Immune SystemThe system in the body responsible for

maintaining homeostasis by recognizing harmful from no harmful organisms and produces an appropriate response

Pathogen: virus, bacteria or other microorganism that causes disease

Antigen: Toxin produced by a foreign invader

AntibodyY shaped protein molecule created by

plasma cells during specific immune response.

Function is to attach to and deactivate antigens/pathogens present in the bloodstream during a specific immune response

Parts of the Immune SystemBlood( white blood cells in particular)Lymph nodesSpleenBone marrow(to produce more WBC’s

There are 2 types of diseases:Noninfectious - often called functional

diseases, whereby an organ does not work properly anymore. (e.g. cancer, heart disease)

Infectious - caused by a disease-producing organism called a pathogen. (e.g. measles, colds, flu, malaria, etc.)

The body’s defenses against pathogens include:

1. Non-specific Defenses

2. Specific Defenses

Body’s Lines of DefenseFirst LineSecond Line –non specific Immune

responseThird Line- specific immune response

1. Non-specific DefensesThese are your first line of defense against

pathogens. They guard against all foreign organisms and not just any one specific organism.

The major forms of non-specific defenses come into action as follows:

(A) Physical and Chemical Barriers

skinmembrane liningssweatsalivastomach acidurinetearsmucus

(B) Inflammatory Response – 2nd line Defenses

It is a reaction that causes redness, swelling, pain, and warmth in the area of infection. Cells damaged by the infection release chemicals, that causes an increase in blood flow to the infected area.

These are defenses that the body uses no matter what the invader may be. These defenses are:A. Phagocytosis- done by macrophagesB. Natural Killers cells- the killer cells kill infected cellsInflammation- cuts off the infected area from the rest of

the bodyFever-raising temperature kills invading microorganisms

This results in WBCs called phagocytes being transported to the site of the infection. The phagocytes ingest the pathogens and damaged tissue, resulting in the formation of puss. This usually kills the pathogen. Sometimes the infection gets to the lymphatic system and causes the lymph nodes to swell.

If the infection is serious, it results in the formation of more phagocytes. If this does not finish the infection, chemicals are released that increase the body temperature. This is called a fever. A fever serves two major purposes:

(i) it kills microorganisms that cannot survive the higher temperature

(ii) it slows down microorganisms, giving the WBCs a chance to destroy them

* If the pathogen is a virus, another defense system occurs. It is called interferon. It is a substance produced by cells infected by a virus. It causes non-infected cells to produce an enzyme that blocks reproduction of the virus.

2. Specific Defenses – 3rd line Defenses

If the pathogen gets past the non-specific defenses, it will encounter the specific defenses. It is at this stage that the immune system comes into play.

These are defenses that the body uses for specific invaders. These defenses includeThe production of antibodiesThe killing of specifically infected body cells and

microbesIt provides the body with the ability to fight

infection through the production of antibodies or cells that inactivate foreign substances or cells.

• The immune system includes all parts of the body that are involved in the recognition and destruction of foreign materials.

• The basis of immunity lies in the body’s ability to distinguish between its own substances (itself) and foreign substances (non-self).

• Any foreign substance that triggers a specific defense response is called an antigen.

• Antigens are usually protein, but can be carbohydrates, lipids or nucleic acids. These are carried on the surface of bacteria, viruses, and other pathogens that may enter the body.

• The response to an antigen is called an immune response.

The Mechanism of specific Immune response

When you become infected with a pathogen the following series of events occurs.

Step 1: The pathogen is attacked by macrophages and they engulf the organism /particle

Step 2: the macrophage displays a form of the antigen on its surface

Step 3: helper T cells recognize the antigen on the surface of the macrophage and it begins two forms of response. One is called cellular immunity and the other is Humoral or blood Immunity

Note: suppressor T cells release substances that slow down the immune response and eventually stop it.

Cellular And Humoral or Blood immunity

Cellular ImmunityHelper T- cells

activates a Cytotoxic T- cell

Cytotoxic T- cell divides T- cells into Cytotoxic T- cells and memory T-cells

Killer T- cells kill infected cells

Memory T-cells remain ready for a second invasion

Humoral or Blood immunity

Helper T -cell activates a B- cell

B- cell divides into plasma and memory B- cells

Plasma cells create antibodies

Antibodies attach to and deactivate pathogens found in blood

Memory B -cells remain ready for a second invasion

Types of Immunity

1. Active ImmunityThe body produces its own antibodies or killer T cells

to attack a specific antigen. Ex. You have a throat infection and you have built up

antibodies against a clod virusYou were given a vaccination for polio so your body built

up antibodies to the polio antigen Active immunity is long lasting. It develops in two

ways:(i) when a person had the disease(ii) by vaccination of a weakened or milder form of the

pathogenVaccination: an injection of a weakened strain of an

infectious microbe that causes the body to produce antibodies without harming the body

2. Passive ImmunityThis is borrowed immunity. The person is

given antibodies from another person or animal who has been infected by the antigen.Ex. Maternal immunity: a mother gives

antibodies to her child while breast feeding. This protects the baby against infection until the baby is ale to produce its own antibodies

It is only temporary - lasting only 30 days, but faster acting then the active immunity response.

Immune System and TransplantsThe immune response can result in

problems with organ transplants. The body recognizes transplanted organs as foreign to the body, and tries to fight them as if they were a pathogen.

The result would be the destruction of the transplanted organ. This is controlled in two ways:

(i) Donor and recipient are closely matched.

(ii) Recipient is given drugs to suppress the immune system.

An immune response can involve two categories of reactions:

B cell reactions

T cell reactions

1. Antigen enters body

2. Macrophage ingests antigen and displays form of antigen on cell membrane

3. T cell recognizes antigen 3. B cell recognizes antigen

4. Helper T cell recognizes antigen displayed by macrophage

5. T cell stimulated to divide by helper T cell to form killer T cells and memory T cells

5. B cell stimulated to divide by helper T cell to form plasma cells and memory B cells

6. Killer T cells bind to virus-infected cells

6. Plasma cells produce antibodies that bind to antigen

7. If antigen enters body again, memory T cells divide to produce new killer T cells

7. If antigen enters body again, memory B cells divide to produce new plasma cells

Types of Immunity Responses

1. Primary Immune ResponseThis occurs when an antigen enters the

body for the first time. It takes 5 days for the body to recognize

the antigen and start production of antibodies.

It takes another 10 to 15 days for the antibodies to build up.

2. Secondary Immune ResponseThis occurs if an antigen that has entered

the body before, enters a second time.There is a shorter response time of only 1

to 2 days for antibody production.Memory B cells – easily recognize the

antigens and produce mass quantities of antibodies in a very short period of time

Memory T- cells- quickly recognize infected cells and kill them quickly

Autoimmune DiseasesAutoimmune diseases are disease where

the immune system begins to attack itself.ex/; Rheumatoid Arthritis- crippling disease

of the jointsLupus-disease of blood and organsMultiple sclerosis-disease of the nervous

systemCauses” unknownCures/ Treatments no cures. Usually treated

with drugs

Allergies and Allergic reactionAllergy- an exaggerated response by the

immune system to an allergenAllergen: a normally harmless substance

that causes an allergic reaction. Ex. Dust pollen mould food insect stings

Types of allergic reactions there are twp types of allergic reactions

Immediate-occurs within seconds and abnormally lasts for about 30 mins

Delayed-takes longer to react and can last for a much longer time

Mechanism of an allergic ReactionDuring an allergic reaction antibodies cause

histamines to be released from certain cellsHistamines

Chemical released into the blood stream that causeSwelling inflammation of tissuesRelease of fluids(runny nose and eyesMuscle spasms(some cases

Anaphylaxis or anaphylactic shock:This is the sudden and severe allergic reaction to

a substance that can cause death

Treatments for allergiesAvoidance of material-especially foodEpinephrine-epi penContains a hormone called epinephrine that

helps restore normal blood pressure during anaphylactic shock

AntihistaminesDrugs such as Benadryl , Sudafed and Actified

contain chemical called antihistamines that help reduce the amount of histamine in the blood. This reduces the allergic reaction

AIDS

Acquired Immune Deficiency SyndromeThe cause of AIDS is a virus called the

human immunodeficiency virus - HIV.The virus attacks the helper T cells of the

immune system.The virus enters the T cell and remains

within the cells for months or even years without producing symptoms.

The virus has a number of disturbing properties:

(1) It is able to mutate giving it the ability to produce different strains. (HIV-1;1981, HIV-2; 1985)

(2) It causes change in the cell membrane of the T cell causing them to fuse together. This allows the virus to pass from cell to cell without entering the bloodstream and becoming exposed to antibodies present in the blood.

• When HIV becomes active, the individual develops AIDS. The virus reproduces, spreads, and destroys helper T cells. The T cells become a HIV factory.

• Some possible triggers for HIV activation are:(i) other co-infections

(ii) contain a gene like a ticking time bomb

The decrease in helper T cells weakens the immune system. The body loses its ability to fight disease and becomes susceptible to opportunistic infections and malignancies.

Spread of AIDS1. Sexually transmitted2. Blood-to-blood contact3. Mother to fetus during pregnancy or at

the time of birth* In rare cases through breast milk

Prevention of AIDS1. Abstinence from sexual activity2. Use of a latex condom, plus spermicidal

nonoxynol-93. Avoid sharing of needles during of

intravenous drug use