Immunobiology

Question 1

Active immunity

Answer 1

the immunity which results from the production of antibodies by the immune system in response to the presence of an antigen. Active immunity is defined as immunity to a pathogen that occurs following exposure to said pathogen. When the body is exposed to a novel disease agent, B cells, a type of white blood cell, create antibodies that assist in destroying or neutralizing the disease agent.

Question 2

AIDS

Answer 2

Acquired immunodeficiency syndrome (AIDS) is a chronic, potentially life-threatening condition caused by the human immunodeficiency virus (HIV). By damaging your immune system, HIV interferes with your body’s ability to fight infection and disease.

Question 3

Allergies

Answer 3

An allergy is a chronic condition involving an abnormal reaction to an ordinarily harmless substance called an allergen. Allergens can include aeroallergens such as dust mite, mold, and tree weed and grass pollen, as well as food allergens such as milk, egg, soy, wheat, nut or fish proteins.

Question 4

Antibody

= immunoglobulin

Answer 4

Antibody, also called immunoglobulin, is a protective protein produced by the immune system in response to the presence of a foreign substance, called an antigen. Antibodies recognize and latch onto antigens in order to remove them from the body. A wide range of substances are regarded by the body as antigens, including disease-causing organisms and toxic materials such as insect venom.

Question 5

Antigen

Answer 5

Substance that is capable of stimulating an immune response, specifically activating lymphocytes, which are the body’s infection-fighting white blood cells.
In general, two main divisions of antigens are recognized: foreign antigens (or heteroantigens) and autoantigens (or self-antigens).
Foreign antigens originate from outside the body. Examples include parts of or substances produced by viruses or microorganisms (such as bacteria and protozoa), as well as substances in snake venom, certain proteins in foods, and components of serum and red blood cells from other individuals.
Autoantigens, on the other hand, originate within the body.
Normally, the body is able to distinguish self from nonself, but in persons with autoimmune disorders, normal bodily substances provoke an immune response, leading to the generation of autoantibodies. An antigen that induces an immune response—i.e., stimulates the lymphocytes to produce antibody or to attack the antigen directly—is called an immunogen.

Question 6

Antiserum

Answer 6

a blood serum containing antibodies against specific antigens, injected to treat or protect against specific diseases.

Question 7

Autoimmune disease

Answer 7

an autoimmune disease is an illness that causes the immune system to produce antibodies that attack normal body tissues. Autoimmune is when your body attacks itself. It sees a part of your body or a process as a disease and tries to combat it

Question 8

B cell

= B lymphocyte

Answer 8

A type of white blood cell that makes antibodies. B lymphocytes are part of the immune system and develop from stem cells in the bone marrow

Question 9

Bone marrow

Answer 9

the soft, sponge-like tissue in the center of most bones, e.g. hip and thigh bones. It contains stem cells. The stem cells can develop into the red blood cells that carry oxygen through your body, the white blood cells that fight infections, and the platelets that help with blood clotting.

Question 10

CD4/CD8 co-receptor

Answer 10

CD4 is a co-receptor of the T cell receptor (TCR) and assists the latter in communicating with antigen-presenting cells.

Question 11

Cell-mediated

immunity

Answer 11

Cell-mediated immunity is an immune response that does not involve antibodies. Rather, cell-mediated immunity is the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.

Question 12

Clonal selection

Answer 12

Clonal selection is a process proposed to explain how a single B or T cell that recognizes an antigen that enters the body is selected from the pre-existing cell pool of differing antigen specificities and then reproduced to generate a clonal cell population that eliminates the antigen.

Question 13

Cytokine (interleukin)

Answer 13

The term “cytokine” is derived from a combination of two Greek words -“cyto” meaning cell and “kinos” meaning movement. Cytokines are cell signalling molecules that aid cell to cell communication in immune responses and stimulate the movement of cells towards sites of inflammation, infection and trauma. Examples of cytokines include the agents interleukin and the interferon which are involved in regulating the immune system’s response to inflammation and infection.

Question 14

Disease

Answer 14

a disorder of structure or function in a human, animal, or plant, especially one that produces specific symptoms or that affects a specific location and is not simply a direct result of physical injury.

Question 15

ELISA test

Answer 15

an enzyme-linked immunosorbent assay, also called ELISA or EIA, is a test that detects and measures antibodies in your blood. This test can be used to determine if you have antibodies related to certain infectious conditions. ELISA is often used as a screening tool before more in-depth tests are ordered.

Question 16

Epitope

Answer 16

An epitope is the part of an antigen that is recognized by the immune system, specifically by antibodies, B cells, or T cells. For example, the epitope is the specific part of the antigen molecule to which an antibody binds.

Question 17

Fever

Answer 17

Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body’s temperature set point.

Question 18

HIV

Answer 18

(human immunodeficiency virus) is a virus that attacks cells that help the body fight infection, making a person more vulnerable to other infections and diseases. It is spread by contact with certain bodily fluids of a person with HIV, most commonly during unprotected sex or through sharing injection drug equipment.
If left untreated, HIV can lead to the disease AIDS

Question 19

Humoral immunity

Answer 19

Humoral immunity is the aspect of immunity that is mediated by macromolecules found in extracellular fluids such as secreted antibodies, complement proteins, and certain antimicrobial peptides. Humoral immunity is so named because it involves substances found in the humors, or body fluids.

Question 20

Immune response

Answer 20

an immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders.

Question 21

Immunity

Answer 21

Immunity refers to the body’s ability to prevent the invasion of pathogens.
Innate immunity. We are all born with some level of immunity to invaders.
Adaptive (acquired) immunity. This protect from pathogens develops as we go through life. …
Passive immunity. This type of immunity is “borrowed” from another source, but it does not last indefinitely. …
Immunizations.

Question 22

Immunological

Memory

Answer 22

Immunological memory is the ability of the immune system to quickly and specifically recognize an antigen that the body has previously encountered and initiate a corresponding immune response.

Question 23

Infection

Answer 23

the invasion and multiplication of microorganisms such as bacteria, viruses, and parasites that are not normally present within the body. An infection may cause no symptoms and be subclinical, or it may cause symptoms and be clinically apparent. An infection may remain localized, or it may spread through the blood or lymphatic vessels to become systemic (bodywide). Microorganisms that live naturally in the body are not considered infections. For example, bacteria that normally live within the mouth and intestine are not infections.

Question 24

Inflammation

Answer 24

is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molecular mediators. The function of inflammation is to eliminate the initial cause of cell injury, clear out necrotic cells and tissues damaged from the original insult and the inflammatory process, and initiate tissue repair

Question 25

Leukocyte

Answer 25

A type of blood cell that is made in the bone marrow and found in the blood and lymph tissue. Leukocytes are part of the body’s immune system. Types of leukocytes are granulocytes (neutrophils, eosinophils, and basophils), monocytes, and lymphocytes (T cells and B cells).

Question 26

Lymphatic system

Answer 26

the tissues and organs that produce, store, and carry white blood cells that fight infections and other diseases. This system includes the bone marrow, spleen, thymus, lymph nodes, and lymphatic vessels (a network of thin tubes that carry lymph and white blood cells).
The lymphatic system has three main functions:
It maintains the balance of fluid between the blood and tissues, known as fluid homeostasis.
It forms part of the body’s immune system and helps defend against bacteria and other intruders.
It facilitates absorption of fats and fat-soluble nutrients in the digestive system.

Question 27

Lymphocyte

Answer 27

A type of immune cell that is made in the bone marrow and is found in the blood and in lymph tissue. The two main types of lymphocytes are B lymphocytes and T lymphocytes. B lymphocytes make antibodies, and T lymphocytes help kill tumor cells and help control immune responses.

Question 28

Macrophage

Answer 28

A type of white blood cell that ingests foreign material. Macrophages are key players in the immune response to foreign invaders of the body, such as infectious microorganisms. They are normally found in the liver, spleen, and connective tissues of the body.

Question 29

MHC proteins

Answer 29

Major histocompatibility complex (MHC), group of genes that code for proteins found on the surfaces of cells that help the immune system recognize foreign substances. MHC proteins are found in all higher vertebrates. In human beings the complex is also called the human leukocyte antigen (HLA) system.

Question 30

Monoclonal antibody

Answer 30

A type of protein made in the laboratory that can bind to substances in the body, including cancer cells. There are many kinds of monoclonal antibodies. A monoclonal antibody is made so that it binds to only one substance. Monoclonal antibodies are being used to treat some types of cancer.

Question 31

Non-specific defense

Answer 31

Non-specific defenses are the body’s first line of defense against diseases. They are not directed against a particular pathogen. Non-specific defenses guard against all infections, regardless of their cause. It is also called as innate immunity. Examples of nonspecific defenses include physical barriers, protein defenses, cellular defenses, inflammation, and fever.

Question 32

Passive immunity

Answer 32

Immunity produced by the transfer to one person of antibodies that were produced by another person. Protection from passive immunity diminishes in a relatively short time, usually a few weeks or months. For example, antibodies passed from the mother to the baby before birth confer passive immunity to the baby for the first 4-6 months of life

Question 33

Pathogen

Answer 33

any disease-producing agent, especially a virus, bacterium, or other microorganism

Question 34

Phagocyte

Answer 34

a type of cell within the body capable of engulfing and absorbing bacteria and other small cells and particles. Phagocytes are cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells. The professional phagocytes include many types of white blood cells (such as neutrophils, monocytes, macrophages, mast cells, and dendritic cells).

Question 35

Phagocytosis

Answer 35

process by which certain living cells called phagocytes ingest or engulf other cells or particles.

Question 36

Primary response

Answer 36

the response that the immune system displays when first exposed to an antigen.

Question 37

Retrovirus

Answer 37

A retrovirus is a type of virus that inserts a copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell.

Question 38

Secondary response

Answer 38

the immune response to a previously encountered antigen.

Question 39

Specific defense

Answer 39

Specific defense mechanism is the ability of the body to develop immunity against specific pathogens, toxins or foreign things. This is possible by a special immune system that produces antibodies and/or activated lymphocytes that attack and destroy specific invading organisms or toxins

Question 40

T cell
(= T lymphocyte:
killer T cell
T helper cell)

Answer 40

A T cell is a type of lymphocyte, which develops in the thymus gland (hence the name) They recognise foreign particles (antigen) by a surface expressed, highly variable, T cell receptor (TCR). There are two major types of T cells: the helper T cell and the cytotoxic T cell. As the names suggest helper T cells ‘help’ other cells of the immune system, whilst cytotoxic T cells kill virally infected cells and tumours.

Question 41

Thymus

Answer 41

part of the lymphatic system, the thymus is a ductless, butterfly-shaped gland lying at the base of the neck, formed mostly of lymphatic tissue and aiding in the production of T cells of the immune system: after puberty, the lymphatic tissue gradually degenerates.

Question 42

Transplantation

Answer 42

Transplantation is the transfer (engraftment) of human cells, tissues or organs from a donor to a recipient with the aim of restoring function(s) in the body. When transplantation is performed between different species, e.g. animal to human, it is named xenotransplantation.

Question 43

Vaccination

= immunization

Answer 43

Vaccination is the administration of a vaccine to help the immune system develop protection from a disease.

Question 44

Pathogen

Answer 44

Any agent causing disease. Usually a living microorganism. Capable of producing infection. Poisons like Arsenic are excluded.

Question 45

Viruses (fill in structure, examples, transmission possibilities)

Answer 45

Multi-celled but can only reproduce inside a plant, animal or person;
Hepatatis; AIDS/HIV; Measles; Warts, Influenza, Covid-19, Chicken Pox, Small Pox, Ebola, Bird Flu, Common Cold;
Droplets
Direct contact with soiled clothes
Close personal contact
Sexual contact
Blood transfusion

Question 46

Bacteria (fill in structure, examples, transmission possibilities)

Answer 46

Tiny one-celled creatures. Can live inside or outside the body;
E.Coli; Salmonella; Lyme Disease; Urinary Tract infection; Stomach Ulcers; Cholera:contamination of food/water by faeces of an infected person
Whooping cough: droplet
Tetanus: contact of deep wound with spores usually from soil
TB: droplets, consumption of infected milk (bovine TB)

Question 47

Fungi (fill in structure, examples, transmission possibilities)

Answer 47

Multi-celled but plant-like similar to tree fungus. Takes nutrition from a plant, tree or animal;
Ringworm, Yeast infection; Athlete’s Foot; Candidasis … ;
Athlete’s foot: walking barefoot swimming pool/showers, sharing footwear
Skin/hair/nail infections, e.g. ringworm: sharing clothing, towels, walking barefoot, touching pets with bald spots

Question 48

Protoza (fill in structure, examples, transmission possibilities)

Answer 48

One celled creatures. Usually spread through water;
Malaria; Dysentery; Giardiasis; Chagas Disease… ;
Dysentery:contamination of food/water by faeces of an infected person
Malaria: Mosquito bite

Question 49

Parasites (fill in structure, examples, transmission possibilities)

Answer 49

Actual complex living organism. Can live in intestinal tract or blood stream;
Round Worm; Tape Worm; Triginosis; Tapeworm: ingesting raw meat of infected grass-eater (cow)

Question 50

Protein (fill in structure, examples, transmission possibilities)

Answer 50

Multi-celled but can only reproduce inside a plant, animal, or person;
BSE Mad Cow disease;
vCJD Disease

Question 51

Portals of entry

Answer 51

• Mouth, eyes, nose or genital openings, or through wounds that breach the skin’s barrier:
• Ingestion (via the gastrointestinal tract)
• Break in the skin (needle puncture, wounds, e.g. bite)
• Absorption (via mucous membrane such as the eyes)
• Inhalation (via the respiratory tract)

Question 52

Describe the lytic cycle of a virus in a host cell

Answer 52

1: The bacteriophage binds to the bacterium
2: The phage DNA enters the host cell
3: The host DNA is digested
4: New phage DNA forms, using nucleotides from former host DNA .
5: the host cell transcribes the phage DNA and translates viral RNA, producing phage proteins.
6: Assamble of new phage is complete. A phage-encoded enzyme causes the cell to lyze.
7: New phage are released to start the cycle again.

Question 53

Describe the lysogenic cycle of a virus in a host cell

Answer 53

1: The bacteriophage binds to the bacterium
2: The phage DNA enters the host cell
3: The phage DNA integrates itself into the bacterial chromosome and becomes a noninfective prophage.
4: the chromosome with its integrated prophage replicates. This can continue through many cell divisions.
5: In rare cases, the prophage excises itself from the host chromosome and the cell enters the lytic cycle.

Question 54

Describe how antibiotics work against bacterial infections:

Answer 54

Antibiotics disrupt essential processes or structures in the bacterial cell. This either kills the bacterium or slows down bacterial growth. Depending on these effects an antibiotic is said to be bactericidal or bacteriostatic.
Bactericidal and bacteriostatic antibiotics
A bactericidal antibiotic kills the bacteria while the bacteriostatic antibiotics stops bacterial growth but does not kill the cells. The human immune system is then needed to clear the infection.
Antibiotic targets in bacteria
There are several different classes of antibiotics. These can have completely different bacterial targets or act on the same target but at a different place.
Antibiotics work by:
• interfering with the construction of the wall, weakening it. The immune system can penetrate the bacterial wall and destroy its contents, literally blowing them up.
• preventing the RNA from accurately reading the DNA. This kink in the assembly line leads to defective or inferior construction materials. Plans go awry. The ribosomes are unable to perform their tasks.
• attacking the ribosomes halting all construction and repair. The remaining few cannot meet the demands of the job and produce defective walls or repairs.
• poking holes in an existing wall breaking down the protective barriers. Antibodies and special immune system cells enter through these holes destroying the bacterium.
These targets are absent or different in the cells of humans and other mammals, which means that the antibiotics usually do not harm our cells but are specific for bacteria.
Narrow-spectrum and broad-spectrum antibiotics
Antibiotics can either have a narrow or broad spectrum of activity. Narrow-spectrum antibiotics are more specific and only active against certain groups or strains of bacteria. Broad-spectrum antibiotics instead inhibit a wider range of bacteria. Narrow-spectrum antibiotics are to prefer since the effect on other, non-disease causing bacteria are more limited. Unfortunately broad-spectrum antibiotics are often used since it can be difficult for doctors to diagnose the correct bacteria in time or when knowledge about how to correctly treat an infection is lacking.

Question 55

Explain why antibiotics are ineffective against viral infections:

Answer 55

Antibiotics cannot destroy viruses because they specifically target the machinery found in bacteria. Since viruses do not contain any of this machinery, the antibiotic does not have a target to attack.

Question 56

Explain how the body distinguishes self from non-self and why this is important:

Answer 56

All of your body’s cells carry specific proteins on their surfaces that help the immune system recognize them as “self.” That’s why the immune system usually doesn’t attack your body’s own tissues. “Non-self” materials have proteins and other substances on their surfaces that the body doesn’t recognize, called antigens. Immune cells called lymphocytes recognize non-self antigens and produce antibodies that bind specifically to each antigen.
A normal immune response consists of the following:
• Recognizing a potentially harmful foreign antigen
• Activating and mobilizing forces to defend against it
• Attacking it
• Controlling and ending the attack

If the immune system malfunctions and mistakes self for nonself, it may attack the body’s own tissues, causing an autoimmune disorder, such as rheumatoid arthritis, Hashimoto thyroiditis, or lupus.

Question 57

Describe and explain non-specific defenses in humans:

Answer 57

The first lines of defense are general, and are not specific to fight against certain types of pathogen. We call this non-specific, and they can be physical or chemical barriers.

Question 58

Physical barriers against infection

Answer 58

Skin The skin covers almost all parts of your body to prevent infection from pathogens. If it is cut or grazed it immediately begins to heal itself, often by forming a scab. This prevents infection as the skin acts as a physical barrier.
This physical barrier is formed from closely-packed epithelial cells. Epithelial cells are found in the skin and inner linings of the digestive and respiratory systems.
Parts of the body that do not have skin have developed other ways to prevent infection. For example, the eyes produce tears which contain enzymes. These enzymes are chemical barriers.
Nose The nose has internal hairs, which act as a physical barrier to infection. Cells in the nose produce mucus. This traps pathogens before they can enter the lungs. When the nose is blown, mucus is removed and any pathogens are trapped within it.
Mucus and
ciliated cells The trachea runs from the nose towards the lungs. The cells that line the trachea also have hairs called cilia, which are much smaller than those in the nose. These are called ciliated cells. The ciliated cells waft their hairs in a motion like a Mexican wave at a football match and move mucus and pathogens upwards towards the throat where it is swallowed into your stomach. Other cells called goblet cells create the mucus in order to trap pathogens. The production of mucus in your airways is a physical barrier.

Question 59

Chemical barriers against infection

Answer 59

Chemical secretions are produced against invading pathogens. Secretions include:

Stomach acid Stomach acid is a chemical barrier against infection. It is hydrochloric acid and is strong enough to kill any pathogens that have been caught in mucus in the airways or consumed in food or water.
Tears and saliva Both tears and saliva have enzymes that destroy bacterial cells by breaking down their cell walls. These enzymes are called lysozymes. Like stomach acid, they are a form of chemical defence against infection.
Mucus Mucus is a sticky substance secreted by goblet cells in the trachea. Foreign particles and pathogens adhere to the surface and cilia sweep the mucus away from the lungs.

Question 60

The inflammatory response

Answer 60

The inflammatory response is a localised defence mechanism used by the body following a physical injury or infection.
In response to injury and infection, specialised immune cells called mast cells release histamine.
Histamine causes blood vessels to widen (vasodilation). This increases blood flow to the area. The increased blood flow leads to an accumulation of phagocytes and clotting elements at the site of infection.
It follows five stages:
1. physical injury or infection
2. mast cells release chemical called histamine
3. histamine stimulates blood vessels to vasodilate and increases permeability of capillaries
4. this causes an increased blood flow
5. phagocytes and clotting elements accumulate at the site of injury or infection

Question 61

Fever

Answer 61

Replication of most viruses is reduced by even a small rise in body temperature.

Question 62

The immune system

Answer 62

The body has a second line of defence to stop or minimise infection. This is called the immune system and mainly consists of two types of white blood cells:
• phagocytes
• lymphocytes

About 70 per cent of the white blood cells are phagocytes. They are part of the body’s immune system, but they do not produce antibodies. Instead, they ingest and destroy pathogens such as bacteria.
Phagocytes recognise pathogens and destroy them by the process of phagocytosis. Phagocytosis involves the engulfing of pathogens and their destruction by digestive enzymes contained in lysosomes.
The phagocyte’s membrane surrounds the pathogen and engulfs it in a vacuole. Enzymes found inside the cell then break down the pathogen in order to destroy it. As phagocytes do this to all pathogens that they encounter, they are called non-specific.
During the immune response phagocytes also release cytokines (proteins that acts as a signalling molecules) which attracts more phagocytes to the site of infection.

Question 63

State the composition of blood and name it’s major functions:

Answer 63

The different components that make up blood = plasma, white blood cells, red blood cells, platelets

Functions:

Carrier of gases, nutrients, and waste products.
Oxygen enters blood in the lungs and is transported to cells. Carbon dioxide, produced by cells, is transported in the blood to the lungs, from which it is expelled. Ingested nutrients, ions, and water are carried by the blood from the digestive tract to cells, and the waste products of the cells are moved to the kidneys for elimination.
Clot formation.
Clotting proteins help stem blood loss when a blood vessel is injured.
Transport of processed molecules.
Most substances are produced in one part of the body and transported in the blood to another part.
Protection against foreign substances.
Antibodies help protect the body from pathogens.
Transport of regulatory molecules.
Various hormones and enzymes that regulate body processes are carried from one part of the body to another within the blood.
Maintenance of body temperature.
Warm blood is transported from the inside to the surface of the body, where heat is released from the blood.
pH and osmosis regulation.
Albumin is also an important blood buffer and contributes to the osmotic pressure of blood, which acts to keep water in the blood stream.

Question 64

Name / describe / explain antibody-mediated mechanisms of antigen disposal

Answer 64

1. Neutralization antibodies bound to antigens on the surface of a virus neutralize it by blocking its ability to bind to a host cell
2. Opsonization binding of antibodies to antigens on the surface of bacteria promotes phagocytosis by macrophages and neutrophils
3. Activation of complement binding of antibodies to antigens on the surface of a foreign cell activates the complement system. Following activation of the complement system, the membrane attack complex forms pores in the foreign cells membrane, allowing water and ions to rush in. The cell swells and eventually lyses

Question 65

Be able to describe the cell mediated and humoral immunity.

Answer 65

Pathogens are detected via B cell receptors on the surface of the B cell or via T cell receptors on the surface of the T cells, which are specific for one antigen. The structure of B cell receptors and T cell receptors resembles immunoglobins. If a pathogen is bound to a B cell receptor / T cell receptor, the B cell / T cell engulfs and digests it (phagocytosis). Afterwards the antigen fragments of the pathogen are integrated in the plasma membrane and presented on the cell surface of the b cell.
At the same time, macrophages lyse pathogens and also present antigen fragments on their cell surface. If an antigen-presenting macrophage binds to a T-helper cell the macrophage releases interleukin 1. This signalling molecule causes T-helper cells to multiply, producing a clone of identical cells. These T-helper cells activate B and T lymphocytes with B and T cell receptors that match in the same antigen.
Humoral response:
If an activated T-helper cell binds to a matching antigen presenting B cell, the T-helper cell releases interleukin 2 causing the B cell to proliferate. A clone of 1000 identical cells is produced. Most of these cells contain a lot of rough ER, which is connected to a high production of proteins. These B cells (or plasma cells) synthesise specific antibodies against the respective pathogen. Per second they release several thousand antibodies.
Cellular response:
Sometimes the humoral response is not sufficient. This is often the case with viral infections because antibodies cannot fight viruses that are inside body cells. This is when cytotoxic T cells (also known as killer T cells) are needed. Similar to B cells, T cells first have to be activated by T-helper cells which release interleukin 2, which causes the proliferation of cytotoxic T cells. Clones are made of the killer T cell. They destroy the infected body cells by either activating programmed cell death (=apoptosis) or by releasing substances which perforate the body cell.
Apart from killer T cells, the proliferation of T cells caused by interleukin 2 also leads to the production of T suppressor cells and memory T cells. T suppressor cells close down the immune response after it has destroyed the pathogens. Memory T cells are long-living cells that start the cellular response very quickly after a second infection with the same pathogen.

Question 66

Describe clonal selection and the basis of immunological memory:

Answer 66

The immune system has the ability to respond to the large and unpredictable range of potential antigens encountered in the environment. This ability is based on clonal selection after antigen exposure. Clonal selection and differentiation of lymphocytes provide the basis for immunological memory.
Clonal selection: Millions of randomly generated B cells form during development. Collectively, they can recognize many antigens, including those that have never been encountered. Each B cell makes an antibody specific to the type of antigen receptor on its surface. The receptor reacts only to that specific antigen. When a B cell encounters its antigen, it responds by proliferating and producing many clones all with the same kind of antibody. This is called clonal selection because the antigen selects the B cell that will proliferate.
Differentiation of lymphocytes: the differentiation of e.g. B -cells into Memory cells and Plasma cells. The memory cells have the function of providing future immunity against the encountered disease, allowing for a stronger and faster immune response in the case of a second infection. Plasma cells produce antibodies specific to the antigen that stimulated their development.

Question 67

Explain how the immune system is able to respond to the large and unpredictable range of potential antigens:

Answer 67

• Clonal selection: The antigen, after having encountered a randomly generated B cell with its specific antigenic receptor in the body, will cause the B cell to proliferate and make clones of itself.
• Differentiation of lymphocytes: Whilst proliferating, the B cell can either differentiate into a plasma cell, which secrete antibodies specific to the invading antigen, inactivating it, or Memory cells. The long living Memory cells have the function of providing a future immunity against the invading antigen, allowing for a faster and stronger immune response if the antigen invades the body a second time.
• The millions of randomly generated B cells that form during development, which can collectively recognize many antigens, even if they were unencountered.

Question 68

Distinguish between naturally acquired and artificially acquired immunity, including reference to the primary and secondary response to infection:

Answer 68

Natural immunity: Usually due to the immunological memory, recovery from many diseases provides us with a natural immunity against those diseases.
Artificially acquired immunity: Inoculation (the introduction of antigenic determinants into the body). Either Immunization ( where the body is inoculated with antigenic proteins, pathogen fragments or other molecular antigens) or Vaccination ( inoculation with whole pathogens that have been modified so that they cannot cause disease).
Primary immune response:
- When an antigen enters the body for the first time it activates the immune system. This is called the primary response.
- The primary response is slow because there aren’t many B-Cells that can maek the antibody needed to bind to it.
- Eventually the body can make enough of the right antibody to overcome the infection. Meanwhile the infected person will show symptoms of the disease
- After being exposed to an antigen, both T- and B-cells produce memory cells. These memory cells remain in the body for a long time. Memory T-cells remember the specific antigen and will recognize it a second time round. Memory B-cells record the specific antibodies needed to bind to the antigen.
- The person is now immune – their immune system has the ability to respond quickly to a second infection.
Secondary immune response:
- If the same pathogen enters the body again, the immune system will produce a quicker, stronger immune response – the secondary response
- Clonal selection happens faster. Memory B-cells are activated and divide into plasma cells that produce the right antibody to the antigen. Memory T-cells activated and divide into the correct type of T-cells to kill the cell carrying the antigen
- The secondary response often gets rid of the pathogen before you begin to show any symptoms (you are immune to the pathogen)
 Natural immunity is achieved after a primary immune response was triggered from a person catching a disease from the environment, prompting the secondary immune response to be faster and stronger
 Artificial immunity is achieved by inoculating a healthy person with antigenic determinants (genetic material from diseases, modified so that they cannot cause disease). The body conducts a primary immune response, increasing its immunological memory without being ill, allowing for a stronger and faster secondary immune response when the same or similar pathogens attack the body.

Question 69

Explain/describe the principles of vaccination: active and passive immunization

Answer 69

Active: This is the type of immunity you get when your immune system makes its own antibodies after being stimulated by an antigen. There are two different types of active immunity:
- Natural – this is when you become immune after catching a disease
- Artificial – this is when you become immune after you have been given a vaccination containing a harmless dose of antigen
Passive: This is the type of immunity you get from being given antibodies made by a different organism – your immune system does not produce any antibodies of its own. Again, there are two types:
- Natural – this is when a baby becomes immune due to the antibodies it receives from its mother, through the placenta and in breast milk.
- Artificial – this is when you become immune after being injected with antibodies from someone else. E.g. if you contract tetanus you can be injected with antibodies against the tetanus toxin, collected from blood donations:

Question 70

MHC Proteins

Answer 70

Function
Present antigens to a T cell receptor in such a way that it can distinguish between self and nonself antigens
Examples
Class 1 MHC protein
Class 2 MHC protein
Explanation:
After a pathogen infects an antigen-presenting cell it is broken down into fragments. These fragments bind to so called MHC class proteins. Together they form a class antigenic peptide complex, which is exported to the cell furface for presentation. This then attracts the attention of a specific cell (e.g killer T-cell)

Question 71

Cytokines

Answer 71

Function
Soluble signal proteins released by T cells, macrophages, and other cells.
Examples
Interleukin 1
Interleukin 2
Explination
They bind to and alter the behavior of their target cells. Different cytokines activate or inactivate B cells, macrophages, and T cells.

Question 72

CD4 / CD8 receptors

Answer 72

Function
To strengthen the bond between the MHC protein complex and its specific cell
Examples
CD4
CD8
Explanation
E.g. CD8 is found I the killer T cell when a antigen-presenting cell is to be killed, allowing for the killer T Cell to achieve a greater bond with the infected cell.

Question 73

Describe the production and application of monoclonal antibodies.

Answer 73

Production: A clone of cells that produce a single antibody can be made artificially by fusing a B cell (which has a finite lifetime and makes a lot of antibody) with a tumor cell (which has an infinite lifetime and can be grown in culture). The resulting hybrid cell, called a hybridoma, makes a specific monoclonal antibody and proliferates in culture.
Applications:
Immunoassays use the specifity of monoclonal antibodies to detect tiny amounts of molecules in tissues and fluids. This is used in e.g. pregnancy tests to detect the hormone made by the developing embryo.
Immunotherapy uses monoclonal antibodies targeted against antigenic determinants on the surface of cancer cells. The coupling of a radioactive ligand or toxin to the antibody makes it into a medical “smart bomb”. In some cases, binding of the antibody itself is enough to trigger a cellular response that destros the cancer.
Passive immunozation: is inoculation with an immediately acting, but not long-lasting, monoclonal antibody. This approach is necessary when therapy must be effective quickly (within hours). Examples of such life threatening situations are cases where a toxic infection of the body has taken place, serious enough that there is no time for the persons own immune system to mount its own defense.
The enzyme-linked immunosorbent assay (elisa) is a common serological test for the prescence of particular antibodies or antigens. (category: immuassays)
1: the direct elisa employs monoclonal antibodies to detect the prescence of a particular antigen in the sample
2: the indirect elisa is used to determine the prescence of a specific antibody (e.g. HIV antibodies) in a specimen such as serum.

Question 74

Antibody classes

Answer 74

• IgD - attached to surface of B cells, important in B cell activation
• IgM - released by plasma cells during the primary immune response; activates complement
• IgG - monomer that is the most abundant and diverse antibody in primary and secondary response; crosses the placenta and confers passive immunity; activates complement
• IgA - helps prevent attachment of pathogens to epithelial cell surfaces: in secretions (tears, saliva, milk); levels decrease during stress; defends against bacteria and viruses
• IgE - binds to mast cells and basophils, causing histamine release

Question 75

Describe and explain problems connected to organ transplantation and ways to reduce these problems:

Answer 75

All our cells have antigens on them. Lymphocytes learn not to attack cells that belong in our bodies (self). Sometimes people need to have organs transplanted, such as heart, lungs or liver. These new organs have antigens on them too. If the antigens are different to our own then it will trigger an immune response. This will mean our immune system will attack and destroy the new organ. This is called organ rejection.
Tissue typing: Rejection is a problem, and so as to prevent it, donors are tissue typed. This means that the donor’s antigens are checked to see if they match the recipient’s antigens. The closer they are the lower the chance of rejection.
Blood Relative. Rejection is less likely if the donor is a blood relative. This is because they are closer genetically and so the chances of their tissue types being the same are greater. It is not unknown for a mother to donate a kidney to her child for example.
Drugs can suppress the action of the immune system so as to prevent the immune system rejecting an organ