Biol 1057 - cell recognition and immune system

Question 1

Outline the tyoes if oathogens and immune systems role

Answer 1

➢Pathogens (foreign substances) such as
o Viruses
o Bacteria
o Fungi
o parasites
➢The immune system has a vital role in protecting the body by
o Killing and removing pathogens
o Destroying cancer cells

Question 2

Explain how the immune system is activated

Answer 2

➢ Antigens (proteins) on the surface of pathogens are
recognised by special receptors on the immune cells.
➢ Triggering a series of processes in the body (Immune
response).

Question 3

Briefly outline the 3 layers of defence

Answer 3

o Physical and Chemical Barriers
* skin, mucosa, epithelial surfaces
o Innate Immune Response
* Specialised cells
* Phagocytosis
* Inflammation
o Adaptive Immune Response
* Specialised Cells
* Antibodies

Question 4

Outline physical and chemical barriers

Answer 4

o Skin
* keratin of the skin prevents microbial growth
o Mucous membranes
* lining the respiratory, digestive, reproductive, and urinary tracts
* cilia that line the upper respiratory tract sweep mucus and trapped particles up into the
throat, where they can be coughed, expelled or swallowed.
o Perspiration, saliva, and tears
* contains antibacterial enzymes.
o Urine
* flushes bacteria from the urinary tract.
o Acid pH
* stomach, vagina
o Normal flora
* microbes in the mouth and intestine.

Question 5

Briefly outline white blood cells

Answer 5

➢Cells of the immune system involved in protecting the body against pathogens.
➢Produced and derived from multipotent cells in the bone marrow known as
haematopoietic stem cells.
➢Found throughout the body, including the blood and lymphatic system
Types of white blood cells are granulocytes (neutrophils, eosinophils, and
basophils), and agranulocytes (monocytes, and lymphocytes [T cells and B cells])

Question 6

Define stem cells and progenitor cells

Answer 6

Stem cells: Cells with the capacity to divide
and differentiate to a wide range of cell types.

Progenitor cells: Cells with the capacity to divide
and differentiate to a narrow range of cell types

Question 7

Briefly outline the lymphatic system

Answer 7

Lymphatic vessels and lymphatic organs
➢ The lymphatic vessels drain excess fluid from the tissues
and return it to the blood.
➢ White blood cells also travel in lymphatic vessels as well
as in the blood.
➢ The lymphatic organs produce and maintain white blood
cells.
➢ Responsible for the production, maintenance, and
distribution of lymphocytes.
➢ Helps defend the body against pathogens.

Question 8

Outline primary and secondary lymphoid organs

Answer 8

➢ Primary lymphoid organs
o Bone marrow: produces all types of blood
cells including stem cells that give rise to all
white blood cells
o Thymus: maturation site for T cells
➢ Secondary lymphoid organs
o Spleen, lymph nodes: sites where white
blood cells are likely to encounter pathogens

Question 9

Outline where lymphocytes, b-cells and T cells are found

Answer 9

Lymphocytes - bone marrow
b -cells - produced and mature in bone marrow
t-cells - produced in one marrow, mature in thymus

Question 10

BRriefly outline the innate immune response

Answer 10

➢If the pathogens escape the physical and chemical barriers they then encounter the
specialised cells of the innate immune response.
➢ Which includes the following processes:
o Inflammation
o Phagocytosis - neutrophils, macrophages, dendritic cells, natural killer
cells etc.
o Protective proteins (in blood, Complement System)
o Fever
➢Immediate Response

Question 11

Outline the inflammatory response

Answer 11

➢ Localised response to injury x
➢ A wound causes tissue injury and presents an entry
point for pathogens.
➢ Injured cells and mast cells release histamine x, which
dilates the blood vessels near the site of injury.
➢ This allows excess blood flow to the site of injury and
allows white blood cells and platelets to enter the
area.
➢ Platelets release clotting factors to repair the wound. x
➢ The first white blood cells to arrive are
neutrophils. x
➢ They phagocytose (engulf) debris, dead cells
and bacteria.
➢ If neutrophils are overwhelmed, they secrete
chemical mediators (cytokines) to attract
monocytes.
➢ Monocytes differentiate into macrophages
which are more powerful and longer-lived
phagocytes than neutrophils.
➢ Nearby cells secrete chemical factors
(growth factors) to repair the damaged area

Question 12

Outline phagocytosis

Answer 12

• Phagocyte moves towards pathogen via chemotaxis and surrounds pathogen as recognises foreign antigen
• Phagocyte cytoplasm engulfs the pathogen into vacuole to form a phagosome
• Phagosome and Lysosome fuse and release digestive enzymes lysozymes
• Which hydrolyse/digest the pathogen/bacteria
• Antigens displayed on the cell membrane

Question 13

Outline protective proteins

Answer 13

• Bind to mast cells and trigger histamine release in inflammatory response
• They can attract phagocytes.
• Bind to the surface of pathogens and tag them for
  phagocytosis.
• They can form a membrane attack complex that produces
  holes in the surface of bacteria, allowing fluid to enter
  the bacteria, causing them to burst

Question 14

Outline the types of protective proteins

Answer 14

➢ Cytokines
o messenger proteins that bind to immune cells and cause them to
divide.
o Attract immune cells to the area or alter their activity e.g. in the inflammatory
response.
o Attract monocytes to the site of injury.
➢ Interferons
o produced by virus-infected cells to alert nearby cells to the infection.
➢ Interleukins
o Largest group of cytokines.
o They facilitate communication between white blood cells.
o Can amplify or dampen immune responses

Question 15

Outline fever

Answer 15

➢ Common reaction to infection causing rise in body temperature.
➢ Can be triggered by cytokines.
➢ Increased body temperature can help fight infection by:
o Directly inhibiting some bacteria and viruses
o Slowing bacterial growth
o Increasing the phagocytic ability of white blood cells

Question 16

Outline the adaptive immune response

Answer 16

➢ When innate (non-specific) defences have failed to prevent an infection,
adaptive defences come into play.
➢ Act specifically against individual targets
➢ Involve lymphocytes (B cells and T cells)
o have the capacity to recognise and kill the pathogens
➢ The immune response turns off once the threat is gone
➢ The immune system “remembers” the pathogen and if it encounters the same
pathogen again it can mount a faster immune response.

Question 17

Briefly define antigens

Answer 17

• Cell surface molecule which stimulates an immune response
• Each lymphocyte can only recognise one specific antigen.

Question 18

Briefly describe the structure of antibodies

Answer 18

(2 heavy chains)
(2 light chains held by disulfide bridges to connect polypeptide chains)
- Binding sites on the variable region have specific tertiary structure complementary to an antigen
- Rest of the molecule known as the constant region
- 5 classes of antibodies (IgG, IgM, IgA, IgD, IgE).

Question 19

How do antibodies lead to the destruction of a pathogen?

Answer 19

• Antigen-antibody complex is formed
• Which leads to the destruction of pathogens through agglutination
• Which enhances phagocytosis

Question 20

Briefly outline T-cells

Answer 20

T cells have receptors that
recognise specific antigens.
➢ T cells can only recognise antigens presented to them by other cells.
o Antigen-presenting cells (APC).
➢ There are two main types of T-cells:
o Cytotoxic T cells: destroy pathogens.
o Helper T cells: secrete cytokines that
control the immune response

Question 21

Outline which cells are APC

Answer 21

➢ Phagocytes
➢ Cells infected by a virus
➢ Transplanted cells
➢ Cancer cells

Question 22

Outline cell mediated immunity

Answer 22

1. Once the pathogen is destroyed, antigens presented on its cell membrane(APC)
2. Complementary acticated T-lymphocyte binds to foreign antigen on APC
3. Activating T-lymphocyte, therefore, produces clones of complementary T helper cell by mitosis(clonal expansion)
4. Cloned complementary T-helper secrete cytokines cells then stimulate:
   =cytotoxic T- cells to kill abnormal body cells
   =B-cells (humoral response)
   =Phagocytes for phagocytosis
   OR become memory cells to respond to another encounter of same pathogen

Question 23

Outline the role of cytotoxic t cells

Answer 23

➢ Bind to virus-infected or cancer cells (target
cells).
➢ Release perforin molecules that punch holes
in the plasma membrane of the target cell
and form a pore.
➢ Deliver granzymes into the pore that cause
the target cell to undergo apoptosis (cell
death).
➢ Cytotoxic T cells then moves on to the next
target cell.

Question 24

Outline B- cells

Answer 24

➢ They have surface receptors (B cell receptor, BCR)
that recognise specific antigens.
➢ They can differentiate into plasma cells that secrete
antibodies identical to the B cell receptor.
➢ B cells are responsible for humoral immunity,

Question 25

Outline humoral immunity

Answer 25

1. Antigen binds to the complementary antibody on membrane of the B-cell to form antigen-antibody complex
2. Antigen enters the B-cell by endocytosis so B-cell becomes an APC
3. Activated complementary T-cell binds to the B-cell causing B-cell to undergo clonal expansion
4. B-cells reproduce by mitosis & differentiate into plasma cells OR MEMORY cells(LONG LIVED)
   - Plasma cells(SHORT LIVED) secrete antibodies with the complementary variable region to antigen

Question 26

Outline innate and adaptive immune response

Answer 26

Question 27

Outline primary and secondary immune response

Answer 27

➢ Primary Response
o First exposure to the antigen.
➢ Secondary Response
o Second exposure to the antigen
o Facilitated by plasma cells
o More rapid
o More antibodies are produced

Question 28

Outline how antibodies are used for therapeutic and diagnostic purposes

Answer 28

Plasma cells secrete monocolonal antibodies
which can be used to:
o Bind to receptors on cancer cells and block their growth
* Herceptin for breast cancer
o Target cytotoxic drugs to specific cells reducing their side-effects.
o Diagnose disease
* hepatitis, chlamydia, prostate cancer
o Pregnancy testing

Question 29

Outline the production of monocolonal antibodies

Answer 29

1. An antigen is injected into a mouse.
2. The mouse naturally produces
   lymphocytes, that in turn produce
   antibodies specific to the antigen that
   was injected.
3. Cells producing the lymphocytes, are
   removed from the mouse.
4. They are then fused with human cancerous cells called myeloma (tumour) cells to form hybridoma
   cells which divide indefinitely.
5. And produce millions of monoclonal antibodies specific to the original antigen.
6. These antibody producing cells are grown and collected in a laboratory.

Question 30

Outline passive immunity

Answer 30

o Passive immunity
* can be produced by the administration of antibodies
* is short-lived
* does not require direct contact with the pathogen
* anti-venom for snake bites
* immunity acquired by the foetus from maternal antibodies crossing the placenta

Question 31

Outline active immunity

Answer 31

o Active immunity
* requires direct contact with the pathogen
* stimulates the individual’s immune system to produce its own antibodies
* is long-lasting
* depends on the presence of memory B cells and memory T cells
* includes the immunity acquired naturally with infection (natural active immunity)
* can be produced by vaccination (artificial active immunity)

Question 32

Outline vaccination

Answer 32

➢ Vaccination results in the production of memory cells that are
quick to respond to a subsequent infection.
➢ For some vaccines, a second administration (booster) is needed to
produce and maintain high levels of immunity.
➢ Herd immunity: when a sufficiently large proportion of the
population is vaccinated, making it difficult for the pathogen to
spread