Unit 6- Response To Infection

Question 1

What cells are responsible for phagocytosis? 3

Answer 1

Phagocytes: neutrophils, monocytes and macrophages

Question 2

How have phagocytes adapted?

Answer 2

Complex cytoskeleton that allows them to change shape
Contain lysozymes
Large

Question 3

Describe phagocytosis:

Answer 3

• phagocytes move through blood/tissue fluid in response to chemicals
• they surround and engulf the foreign body (phagocytosis)
• microbes are trapped in phagosome which fuses with lysosome
• the lysozymes hydrolyse the microbe proteins, carbs and fats

Question 4

Where do the different phagocytes work?

Answer 4

Neutrophils -blood

Macrophages and monocytes - tissue fluid/lungs and other spaces

Question 5

What causes inflammation?

Answer 5

Granulocytes release chemicals (prostaglandins and histamines) which stimulates inflammation

Question 6

What changes occur in inflammation? Name 4

Answer 6

• vasodilation
• capillary leakage (so phagocytes and granulocytes can enter)
• sensory neurone impulses (tender areas)
• blood clotting
• fever (the heat kills more pathogens than human cells)
• tissue repair (collagen deposits and stimulation of new cell growth makes scar tissue)

Question 7

What make up the non-specific immune response?

Answer 7

Phagocytosis and inflammation

Question 8

What cells make up the specific immune response?

Answer 8

B-lymphocytes and T-lymphocytes

Question 9

How do we know the specific immune response is a later evolutionary advancement?

Answer 9

Only vertebrates have it as the cells that are involved are made in the bone marrow

Question 10

What are antigens?

Clue: antigen is short for (ANTIbody GENerators)

Answer 10

Large molecules that bind to lymphocytes triggering a specific immune response

Question 11

Which cell makes antibodies?

Answer 11

B-lymphocytes

Question 12

What is an antibody?

Answer 12

A protein molecule that can bind specifically to an antigen

Question 13

Structure of an immunoglobulin:

Answer 13

4 polypeptide chains (2 heavy and 2 light chains)
Joined by disulphide bonds to form a Y shape
They all have the same constant region (stem) and different variable regions (different amino acid sequences)
Which leads to a highly specific antigen-antibody complex

Question 14

What is self recognition?

Answer 14

When cells are able to recognise the cell is not foreign by the distinct marker proteins (MHCs) on the cell membrane

Question 15

What are receptors and where are they found?

Answer 15

They are proteins witch only 1 binding site (unlike antibodies 2) found on surface of T-lymphocytes

Question 16

What do receptors do?

Answer 16

They bind to specific antigens forming an antigen-receptor complex

Question 17

What is the main antigen presenting cell?

Answer 17

Macrophage phagocytes as they are in largest abundance

Question 18

What is the macrophages role in the first step of infection from antigens?

Answer 18

In order to initiate the specific immune response a macrophage needs to engulf the pathogen and present the antigen on its surface becoming an antigen-present cell

Question 19

What are cytokines and what cell releases them?

Answer 19

They are chemicals which stimulate clonal selection, released from macrophages and T-helper cells

Question 20

Describe clonal selection from antigen presenting cell:

Answer 20

Eventually a helper T cell with a complementary receptor to the antigen will bind to antigen
The T helper cell releases cytokines which stimulate immature T and B lymphocytes to activate, proliferate and differentiate
The activated cells divide by mitosis making a clone army of cells with identical binding sites that is specific to the foreign antigen

Question 21

How do T killer cells kill the infected cells?

Answer 21

• bind to antigens on infected cells
• secrete porin proteins
• porin makes pores in the cell membrane so water diffuses in
• the infected cell bursts (lysis)

Question 22

What cells are part of cellular immunity?

Answer 22

Cytotoxic/killer T cells and memory T cells

Question 23

Which cells are part of the humoral immunity?

Answer 23

B-lymphocytes which differentiate into thousands of plasma cells
Memory B cells

Question 24

What is the job of plasma cells?

Answer 24

To synthesise antibodies specific to the antigens

Question 25

Why is it called humoral immunity?

Answer 25

Because antibodies are being secreted into the blood plasma (humour)

Question 26

How do antigens prevent infection?

Answer 26

• agglutination
• opsonisation (marking a pathogen for phagocytosis)
• binding to antigens on virus’ or bacteria prevents them attaching to host cells (blocks antigens)
• precipitation, binding to free soluble toxin proteins (blocking/changing their shape) making them insoluble
• lysis

Question 27

Why do some of the activated B and T cells divide into memory cells?

Answer 27

Memory cells remain in the blood for years

• if the same antigen is encountered again memory cells divide quickly into plasma cells and killer cells
• this skips clonal selection
• secondary immune response

Question 28

What is antigenic variability?

Answer 28

When pathogens develop new strains with different antigens

• due to mutation
• we cannot become immune

Question 29

What is vaccination?

Answer 29

• injecting a person with a modified non-virulent strain to promote a primary immune response and make memory cells to that specific antigen
• when the real strain invades the secondary immune response will be able to recognise and kill it quickly

Question 30

What is active immunity?

Answer 30

Any process that promotes a primary immune response leaving memory cells
Eg. Vaccination or catching a disease

Question 31

What is passive immunity?

Answer 31

When antibodies are received

Eg. Breastmilk or across the placenta

Question 32

When does passive immunity happen naturally?

Answer 32

When antibodies are passed across the placenta to the baby

In breast milk

Question 33

When does passive passive immunity happen artificially?

Answer 33

Achieved through injection of antibodies in an antiserum

Eg. To combat AIDS

Question 34

Why could some people not receive vaccines?

Answer 34

• newborns with weak immune systems
• people with immunosuppressant diseases
• those undergoing chemotherapy

Question 35

What is herd immunity?

Answer 35

When the majority of a population (85-95%) are vaccinated, so there are not enough hosts for the disease to survive and reproduce

Question 36

What are free riders?

Answer 36

People who choose not to get vaccinated compromising the threshold for herd immunity

Question 37

What are T suppressor cells?

Answer 37

Cells that stop the response when an antigen has been removed, so the response doesn’t get too over the top and you begin wasting resources

Question 38

Purpose of T helper cell?

Answer 38

To stimulate a specific immune response

Question 39

Explain how the non specific immune response protects against infection by bacteria

Answer 39

• bacteria don’t have MHCs so are recognised as foreign
• phagocytes engulf the bacteria
• neutrophils engulf and digest bacteria
• monocytes become macrophages which also ingest and digest bacteria
• they release cytokines to attract other phagocytes to site of infection, increasing blood flow and inflammation

Question 40

Describe the interaction of immune cells in producing a hormonal response

Answer 40

• macrophages present antigen to activate T helper cells

- T helper cells activate B cells by recognising antigen and producing cytokines

Question 41

Similarities of humoral and cell mediated response

Answer 41

• both are specific to an antigen
• both require the formation of APCs and the presence of MHCs
• both involve clonal selection which is activation of only those cells which recognise the antigen
• both involve differentiation of cells, following activation by T helper cell