Homework Questions "The Immune System"

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1. Explain how the skin and mucous membranes act as barriers against microbes.

The skin and mucous membranes form a barrier that prevents most pathogens from entering the body. The other layers of the skin are tough and form a physical barrier. These dry, keratinised layers of skin discourage pathogen growth. The skin also produces a thin layer of acid and oils. Mucus contain an enzyme called lysozyme which kills bacteria.

2. Outline how phagocytic leukocytes ingest disease-causing organisms in the blood and in the body tissues.

 Phagocytes are a type of leukocytes which ingest and destroy foreign matter through phagocytosis.
1. They can easily move through the walls of blood capillaries and the site in which there is an infection.
2. A phagocyte comes in contact with pathogen cells and does not recognize the glycoprotein struture on its cell wall.
3. The pathogen is then ingested through endocytosis. Plasma membrane forms around pathogen.
4. Pathogen vacuole then binds with lysosome containing digestive enzymes which break down the pathogen.
5. Large numbers of phagocytes form pus.

3. Explain the production of antibodies

Macrophages consume bacteria with antigen molecules in their membranes.
Macrophages present these antigens on their membranes with the help of special protein structures.
Helper T-cells come in contact with macrophages, pick up the antigens, and incorporate them into their own protein structures - this will allow them to present the antigens to B-cells. This also causes the activation of the Helper t-cells.
Activated helper-T-cells activate B-cells by passing their antigen to B-cell receptors.
The B-cells then divide to form clones of antibody-secreting plasma cells and memory cells.

Antibodies are made by lymphocytes, which recognize an enormous number of antigens, but each individual cell recognizes only one type of antigen. Each lymphocyte puts some of the antibody that it makes into its cell surface with the antigen-combining site projecting outwards. When a pathogen enters the body, its antigens bind to the antibodies in the cell surface of one type of lymphocyte. The selected lymphocyte proliferates to give rise to a clone of identical cells bearing receptors for the selecting antigen. Some of the cells develop into short-lived plasma cells that secrete antibody specific for the antigen. Others develop into long-lived memory cells that can respond rapidly upon subsequent exposure to the same antigen.

4. Explain the roles of B-cells, MHC proteins, helper T-cells, cytotoxic T-cells, memory cells and immunoglobines in the antigen/body response.

B cell: a type of lymphocyte normally involved in the production of antibodies to combat infection. It is a precursor to a plasma cell. During infections, individual b-cell clones multiply and are transformed into plasma cells, which produce large amounts of antibodies against aparticular antigen on a foreign microbe. This transformation occurs throughinteraction with the appropriate cd4 t helper cells. Lymphocytes that are capable of producing antibodies in response to detecting the presence of aparticular [[antigen.

MHC molecules typically interact with the cell surface receptor of a type of lymphocytes known as killer T cells. The receptor on the killer T cell binds to the MHC molecule and informs the killer T cell on whether that cell is normal or not. The interesting part of the story is how the T cell can distinguish the MHC class I protein on a normal cell from that on an abnormal one. The key concept here is to appreciate that the MHC molecule has within its structure a groove. Into this groove is bound a small piece of protein derived from within the cell, that was placed there during the synthesis of the MHC molecule. If this peptide of 8 or 9 amino acids happens to be a foreign peptide, such as one produced by a viral gene, or a cancer gene, the T cell will become activated, and attack the infected or cancerous cell. Of course there many more details involved in this process. Of primary interest to medicine and the average person is the fact that when an organ is transplanted between non-identical people, it is the recipient's T cells reacting against the donor organ MHC (Major Histocompatibility Complex) proteins that causes much of organ rejection.
Helper T: This type of T lymphocyte releases lymphokines upon stimulation of specificantigens to promote the activation of B lymphocytes as well as killer T lymphocytes.

Cytotoxic T-cell: lymphocyte-like effector cells which mediate antibody-dependent cell cytotoxicity. They kill antibody-coated target cells which they bind with their fc receptors.
Memory T- cell: The long lasting immune memory is humoral and resides in b-cells, although it appears that persistence of the antigen may be essential. T-cell memory is shorter. A type of [[lymphocyte that is released as a [[specific immune response that is stored in case the specific [[ antigen attacks once again. Live vaccinations are used to initiate the production of [[memory cells.
Immunoglobin: (1) Any of several classes of structurally related proteins in the blood serum, produced by plasma cells as an immune response against foreign agents (antigens).
(2) The fraction of the blood serum containing antibodies.

5. Describe the production of monoclonal antibodies along with one use of them in diagnosis and one use in treatment.

Monoclonal antibodies - large quantities of a single type of antibody, produced using the procedure outlined below:
:*Production
1. Antigens that correspond to a desired antibody are injected into an animal.
2. B-cells producing the desired antibody are extracted.
3. Tumor cells are obtained from another source (tumor cells grow and divide endlessly).
4. B-cells are fused with tumor cells, producing hybridoma cells that divide endlessly, providing the desired antibodies.
5. The hybridoma cells are cultured and antibodies they produce are extracted and purified.
 Treatment of rabies

6. Outline the principle of challenge and response, clonal selection and memory cells as a basis of immunity.

B cells make antibodies.
The immune system can make 10^15 different types of antibodies (but not all at once).
A few of each type of B cell are produced and they wait until the body is infected with an antigen.
When this occurs, they multiply to form many clones; this is called Clonal Selection.
A clone of B cells can produce large amounts of antibodies quickly and give immunity to a disease, only after the immune system is challenged by a disease -- this is called the challenge and response system. The immune system needs to be "challenged" by a disease, usually in the form of an antigen present upon it, and then the immune system responds by producing a clone of "B" cells which produce large amounts of antibodies to fight and eliminate the pathogen

7. Define the terms: pathogen, active immunity, passive immunity, natural immunity, and artificial immunity

Pathogen: an organism or a virus that causes a disease.
Active immunity - Immunity due to antibody production by the organism following the invasion by pathogens.
Passive immunity - Immunity due to antibodies received from another organism which made them as a result of that particular organism's own active immunity.
Natural immunity - Immunity as the result of infection with a pathogen, as per the challenge and response method.
Artificial immunity - Immunity as the result of a vaccine which contains antibodies that are used to fight the pathogen.

8. Outline the process of immunization

A weakened or dead version of a pathogen is injected into the body, causing the immune system to mount a primary response.
This results in the production of B memory cells.
The B-cells "remember" the antibodies to produce in response to the pathogen.
When the real pathogen strikes, a secondary response occurs, aided by the memory cell production of pathogen-specific antibodies.
This response is much stronger than the primary repsonse and prevents any ill effects.

9. Discuss the benefits and danger of immunization against bacterial and viral infection.

 Benefits of vaccination
 Some diseases, such as small pox, can be eradicated.
 Deaths can be prevented, ex. from measles.
 Long-term disabilities can be prevented
 Rubella in pregnant women can lead to birth defects
 Mumps can cause infertility in men.
 Dangers of vaccination
 Immunity developed after vaccination may not be as effective as immunity developed in response to the actual disease.
 Dangers of side effects of some vaccines include:
 Whooping cough, vaccine can cause brain damage.
 Pregnant women, cancer patients, and others can be harmed by cross-infection from people vaccinated with the live virus, ex. smallpox vaccine.

10. State one example of an infectious disease caused by each of the following groups: viruses, bacteria, fungi, protozoa, flatworms, and roundworms.

Viruses: HIV
Bacteria: Cholera
Protozoa: Malaria
Fungi: Ringworm
Flatworms: pork tapeworm
Roundworms: Hookworm

11. List six methods by which disease causing agents are transmitted and gain entry to the body.

Airborne/inhalation
Direct contact
Cuts
Ingestion of contaminated food or water
Sexual intercourse
Insects
Blood transfusions

12. Explain the need for immunization against the bacterial infections: diphtheria, whooping cough and tetanus and against the viral infections: measles, polio, and rubella

• Artificial immunization involves the use of vaccines, which are pathogens that have been killed or weakened so they are no longer harmful.
• Different vaccines are introduced into the body by different routes: into the muscle; into the skin; into the lungs; etc.
• After the first exposure to a vaccine (or any antigen), no antibodies are present in the blood for several days. Then there is a slow rise of antibodies in the blood, followed by a gradual decline. This gradual rise and decline is known as the primary response.
• Many of the B-cells that are produced during the primary response continue to circulate as memory cells, which can last for years or decades. Memory cells patrol for the return of a particular antigen.
• The memory cells are numerous so if they do encounter the appropriate antigen they carry out a secondary response, which is much faster than the primary response. Thus memory cells can terminate an infection before the individual gets sick. Hence the advantage of immunity.
• Following a secondary response, antibodies in the blood rise rapidly to a level that is much greater than before. Therefore many vaccines are given twice; the second vaccination is called the 'booster' because it greatly boosts the number of antibodies.

13. Describe the cause, transmission, and effects of one human bacterial disease

 Cholera: is a waterborne disease caused by the bacterium Vibrio cholerae.
Cause: Cholera is caused by the bacteria Vibrio cholerae which produces potentially lethal secretory diarrhea.
Transmission: Cholera is transmitted through the ingestion of feces contaminated by the bacteria. The contamination usually occurs when sewage gets into drinking water. It's a huge problem in developing countries, which lack a developed sewage system, and also right after natural disasters such as floods. The recent Tsunami brought fears of Cholera.
Effect: Cholera causes a lethal secretory diarrhea and dehydration. Other symptoms may include cramping, fever, and nausea.

14. What does HIV stand for?

human immunodeficiency virus

15. Draw a labeled diagram of an HIV particle.

see diagram

16. List the methods by which HIV can be transmitted

 HIV doesn't survive outside of the body and can't easily pass through the skin. Transmission involves the transfer of body fluids from an infected person to an uninfected one.
1. Through small cuts or tears in the vagina, penis, mouth or intestine during vaginal, anal or oral sex.
2. In traces of blood on a hypodermic needle that is shared by intravenous drug abusers.
3. Across the placenta from a mother to a baby, or through cuts during childbirth or in milk during breast feeding.
4. In transfused blood or with blood products such as Factor VIII used to treat haemophiliacs.

17. Outline the effects HIV on the immune system

HIV attacks T-cells which are part of the immune system that are important for the formation of Beta lymphocytes. The virus enters the T-Cells and replicates there. As reproduction increases, the cell breaks up and the virus RNA is spread to other T-cells. The virus keeps infecting and killing other T-cells, paralyzing the immune system. This enables other organisms usually kept under control by the immune system to be able to affect the body.

18. What is AIDS, and how is it linked to HIV?

AIDS or Acquired Immunodeficiency Syndrome is a collection of symptoms and infections caused by infection with the human immunodeficiency virus (HIV).

19. List at least three social implications of AIDS

Social Implications Fear and apprehension for those associated with the disease, the lifestyle associated with the disease is attacked, trouble getting a job or even getting health insurance- distanced from society

20. Copy figure 43.20 from p. 861 textbook

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