Immunity

Question 1

Define immunity

Answer 1

Tha ability of the body to protect itself from pathogens. It is comprised of specific & non-specific mechanisms

Question 2

Describe non-specific defenses and give examples

Answer 2

Non-specific defenses:
Skin acts as a primary defense, consists of a dead layer of skin cells providing a physical inert barrier, secretes sebum to inhibit pathogen growth
Mucus membranes also are a primary defence, sticky mucus is secreted to trap pathogens, contains lysozymes which break & destroy bacteria

Question 3

Describe the process of phagocytosis

Answer 3

1. Pathogens produce chemicals alerting phagocytes, and recognise antigens as foreign
2. Phagocyte attaches to the pathogen, engulfs the pathogen
3. Phagocyte encloses pathogen in its vacuole forming a phagosome
4. lysosomes merge with the phagosome forming a phagolysosome
5. Lysosomes release enzymes that break down the pathogen
6. After digestion harmless products are absorbed and the waste is removed via exocytosis

Question 4

Describe specific defences

Answer 4

This is body’s response to specific bacteria. It is characterized by its specificity & memory. As invading organisms are distinguished from one another, enabling faster response to pathogen next invasion
Foreign pathogens have specific antigens on their surface which the body is able to recognise allowing specific responses to be carried out

Question 5

What are the 2 types of lymphocytes?

Answer 5

T & B lymphocytes

Question 6

How are T cells formed?

Answer 6

Lymphocytes destined to become t-cells migrate to the thymus. immature lymphocytes leave the thymus and encounter their antigen
Each T cell has a t-cell receptor which is specific to a particular antigen. T lymphocytes that survive thymic selection will mature and leave the thymus. After that, they circulate through peripheral lymphoid organs, ready to encounter their antigens and become activated.

Question 7

How are B cells formed?

Answer 7

B cells develop their immunocompetence in the bone marrow.
Positive selection ensures that only B cells with functional receptors are allowed to develop further. This occurs when the B cell receptor successfully binds its ligand, which induces survival signals.

Negative selection happens when B cells respond to self-antigens in the bone marrow and, as a result, undergo receptor editing, anergy, or apoptosis. This promotes central tolerance and minimises the risk of autoimmune reactions when they eventually mature and move to the peripheral circulation.

Once differentiated in the bone marrow, B cells migrate to lymphoid follicles in the spleen. They also migrate to areas where lymphoid activation and defense are likely to be triggered such as in the mucosal linings. This includes the Peyer’s patches

Question 8

What are the 3 different types of B cells & their functions?

Answer 8

B cells are involved in the humoral response (bacteria)
B memory cells remain in the blood for years, act as an immunity store. They are programmed to remember specific antigens on a pathogen enabling a rapid response
B effector cells divide via mitosis to form plasma clones
Plasma cells produce antibodies

Question 9

What are the 4 different types of T cells and their functions

Answer 9

T killer cells: Directly attack pathogens, attack foreign material, they produce perforin which penetrates cell wall, making the pathogen cell leaky
T regulator cells: involved in suppressing the immune system, is a protective measure as it prevent an autoimmune response. It ensures the body can recognise it’s own antigens
T helper cells: release cytokines & activate other immune cells. They have CD4 receptors which bind to antigens on antigen presenting cells. Produce interleukins which stimulate the production of B cells
T memory cells: provides long term immunity & act as a memory store. These cells stay & circulate in the blood. If foreign antigen is detected it stimulates mitosis to produce T killer cells that attack the pathogen

Question 10

Define immunocompetence

Answer 10

The ability of the body to have a normal immune response

Question 11

Define Agglutination

Answer 11

Some antibodies have many different binding sites, this allows multiple antigens to bind to a single antibody, allowing the clumping of pathogens together. This prevents the spread of pathogens throughout the body. making it easier for phagocytes to engulf many pathogens at once

Question 12

Define precipitation (immune response)

Answer 12

Some antigens are soluble and so antibodies precipitate them out to be engulfed by phagocytes

Question 13

Define cell lysis

Answer 13

‘cell death’
After attachment of antigens, antibodies release chemicals, e.g., cytokines to attract enzymes to break down of foreign cells

Question 14

Define neutralization

Answer 14

Some pathogens produce toxic chemicals, the binding of the antibodies neutralise it, making it harmless

Question 15

Describe the role of opsonin’s

Answer 15

Acts as binding sites, are specific and non-specific. Allows more phagocytes to engulf pathogens. Prevents the entry of pathogens into host cells

Question 16

Describe the process of antibody production
(Humoral immunity)

Answer 16

1. A b cell has an antibody receptor on it’s cell surface which is specific to the antigen shape that has entered the body
2. The selected B cell divides via mitosis, memory and plasma cells are produced
   3.Plasma cells secrete antibodies that are specific to the antigen
3. If the antigen enter the body for a 2nd time. The memory cells produced during 1st invasion divide to form plasma cells in order to produce specific antibodies that are needed. Occurs much quicker than stages 1-3

Question 17

What are the 5 types of antibodies?

Answer 17

IgG- main antibody able to cross placenta

IgA- secretory antibody

IgM- released into plasma, indicates current infection

IgE- associated with parasites and allergic reactions

IgD- attached to B cells & act as antigen receptor

Question 18

What is the purpose of memory cells?

Answer 18

B cells and T cells produce memory cells which stay in the blood, these memory cells keep a memory of invading pathogen, allows them to have a faster response if infected with again. This makes second response much quicker; pathogen may be killed before we show symptoms

Question 19

What is the difference between primary & secondary response

Answer 19

Primary involves first exposure to a pathogen, is a small,slow & ineffective process, and symptoms are likely to be present from day 6
Secondary is a rapid, large & effective response, Lots of antibodies produced in a short amount of time. Pathogen has been seen before, likely to kill pathogen immediately before showing of symptoms. Less likely to show symptoms

Question 20

What are the 4 types of immunity?

Answer 20

Natural active, Natural passive, Artifical active & artificial passive

Question 21

Define Natural active immunity

Answer 21

These are the antibodies produced when infection is present. The immune system has detected and reacted to foreign antigens and has produced antibodies & memory cells to remember pathogen. Is a long-term form of immunity

Question 22

Define natural passive immunity

Answer 22

This refers to the passing of a mothers antibodies to her baby via breast milk. The baby become immune to what their mother is immune to. This is a short-term form of immunity an as no memory cells are made

Question 23

Define artificial active immunity

Answer 23

An injection of a harmless or dead pathogen, a vaccination stimulates the immune system to produce a response, and antibodies are produced along with memory cells, giving long-term immunity

Question 24

Define artificial passive immunity

Answer 24

An injection of antibodies made by someone else. Is a short-term form of protection as no memory cells are made.
Involves injection of immune serum

Question 25

Define autoimmune

Answer 25

Where the body is unable to recognize it’s own cells so attacks them and produces antibodies against own antigens

Question 26

Give 3 examples of autoimmune conditions and their effects

Answer 26

Type 1 diabetes, involves attacking of insulin secreting cells (beta), insulin cannot be produced as a result, blood glucose levels cannot be regulated as a result
Rheumatoid arthritis- destroys the cartilage cells of the joint,
MS- destroys mylein sheath on neurones, affects speed of conductivity of signals
Glomerulonephritis: destroys nephrons in the kidney

Question 27

What are the treatments associated with autoimmune diseases?

Answer 27

Immunosuppressant drugs, suppress the immune system from a response, but make people more vulnerable to secondary infection
Transplant of defective organ
Steroids to help with chronic pain
Insulin injections needed for type 1 diabetes

Question 28

What is an allergy?

Answer 28

An allergy provides a reaction to a substance that most people are tolerant of e.g., peanuts
Allergens are a form of antigen that cause allergies

Question 29

Describe the allergic response

Answer 29

1. The allergen invades the body
2. Plasma cells produce large amounts of IgE antibody against the allergen
   3.IgE antobody attaches to the mast cells that are circulating
3. Mast cell makes contact with allergen, triggers degranulation
4. Chemical such as histamine are released
   promotes swelling, redness, heat, vasodialtion of capillaries

Question 30

Describe types of hypersensitivity reaction

Answer 30

1: Anaphylactic shock: involves the breakdown of mast cells & basophils resulting in shock
2: Cytotoxic reactions: an atypical blood transfusion destroying cells
3. Immune complex reactions: results in tissue damage e.g., rheumatoid arthritis
4. Delayed hypersensitivity reactions: occurs 12-72 hours after exposure, e.g., mantoux test for Tb

Question 31

Describe the process of cell-mediated immunity

Answer 31

T lymphocytes response to viral infections
1. T helper cells become activated, macrophages engulf the pathogen and display it on their surface, forming APC (antigen-presenting cells)
2. A specific T helper cell is chosen, has an antibody that is specific to APC
3. cytokines are released which stimulate more t-helper cells to be made forming t-helper clones
4. t-helper clones stimulates the production of b cells to make antibodies. Also stimulates phagocytosis allowing the pathogen to be engulfed
5. Once pathogen is destroyed T-regulator cell is deactivated and the immune system becomes suppressed