Response to infection

Question 1

What do the non-specific immune response and the specific immune response make up?

Answer 1

The primary response

Question 2

What are antigens?

Answer 2

Molecules (usually proteins or polysaccharides) found on the surface of cells

Question 3

Which immune response happens first?

Answer 3

The non-specific immune response

Question 4

What is the non-specific immune response?

Answer 4

It is non-antigen specific so occurs in the same way for all microorganisms regardless of the foreign antigen they have

Question 5

What 3 mechanisms are part of the non-specific immune response?

Answer 5

1. Inflammation at the site of infection
2. Production of interferons (anti-viral proteins)
3. Phagocytosis and lysozyme action

Question 6

Non-specific immune response 1: describe inflammation at the site of infection

Answer 6

The site of infection becomes red, warm, swollen, and painful = inflammation

Question 7

Non-specific immune response 1: how does inflammation work?

Answer 7

• The immune system recognises foreign antigens on pathogen surface and releases molecules that trigger inflammation
• Molecules cause vasodilation increasing blood flow to site = lots of immune system cells brought
• Molecules also increase permeability of blood vessels = allows immune system cells to move out of blood cells into the tissue
• Pathogen can be destroyed

Question 8

Non-specific immune response 2: what do interferons do?

Answer 8

Interferons help prevent viruses spreading to uninfected cells

Question 9

Non-specific immune response 2: how do interferons work?

Answer 9

• They inhibit the production of viral proteins which prevents viral replication
• They activate cells in the specific immune response to kill infected cells
• They activate other mechanisms of the non-specific immune response eg inflammation

Question 10

Non-specific immune response 3: what is phagocytosis?

Answer 10

Engulfment of pathogens using phagocytes (type of white blood cell) which are found in the blood and tissues

Question 11

Non-specific immune response 3: what cells are the first to respond to a pathogen in the body?

Answer 11

Phagocytes

Question 12

Non-specific immune response 3: How does phagocytosis work?

Answer 12

• A phagocyte recognises antigens on the pathogen and engulfs it using the cytoplasm = phagocytic vacuole is formed
• A lysosome fuses with the phagocytic vacuole and the lysozymes break down the pathogen
• The phagocyte presents the pathogens antigens on its cell surface to activate other immune system cells

Question 13

What is the specific immune response?

Answer 13

A response that is antigen specific that targets specific pathogens and involves T and B cells

Question 14

Specific immune response: what type of cell is a B cell?

Answer 14

White blood cell covered with antigen-specific receptors

Question 15

Specific immune response: how do phagocytes activate T cells?

Answer 15

• Receptors on T cells bind to complimentary antigens on antigen-presenting cells ie phagocytes = each T cell will bind to a different antigen
• The T cell is activated and divides to produce clones of itself

Question 16

Specific immune response: what are the different types of T cells + explain?

Answer 16

T helper cells – release substances to activate B cells, T killer cells and macrophages
T killer cells – attach to antigens on a pathogen-infected cell and kill it
T memory cells – involved in immunity

Question 17

Specific immune response: what type of cells are B cells?

Answer 17

White blood cells that are covered in proteins called antibodies that are specific

Question 18

Specific immune response: what do antibodies do?

Answer 18

Bind to antigens to form an antigen-antibody complex

Question 19

Specific immune response: how are B cells activated?

Answer 19

T helper cells activate B cells alongside an antibody of a B cell binding to an antigen

Question 20

Specific immune response: what do activated B cells turn into?

Answer 20

They divide by mitosis into plasma cells (B effector cells) and B memory cells

Question 21

Specific immune response: what are plasma cells?

Answer 21

Clones of B cells that secrete antibodies specific to an antigen into the blood which will form lots of antigen-antibody complexes

Question 22

Specific immune response: describe the structure of an antibody

Answer 22

Antibodies are made of four polypeptide chains – two heavy and two light
Each chain has a variable region and a constant region

Question 23

Specific immune response: what are the variable regions on an antibody?

Answer 23

They form the antigen binding sites and are complementary in shape to the particular antigen

Question 24

Specific immune response: what are the constant regions on an antibody?

Answer 24

Allow binding to receptors on immune system cells eg phagocytes and is the same in all antibodies

Question 25

Specific immune response: what is a hinge region?

Answer 25

Allows flexibility when the antibody binds to the antigen

Question 26

Specific immune response: how many binding sites do antibodies have?

Answer 26

Two so an antibody can bind to two pathogens at the same time

Question 27

Specific immune response: what three ways do antibodies help to clear infections?

Answer 27

1. Agglutinating pathogens
2. Neutralising toxins
3. Preventing the pathogen binding to human cells

Question 28

Specific immune response: describe how antibodies agglutinate pathogens

Answer 28

An antibody can bind to two pathogens at the same time causing them to become clumped together – then engulfed by phagocytes

Question 29

Specific immune response: describe how antibodies prevent pathogens binding to human cells

Answer 29

When antibodies bind to antigens, they block the cell surface receptors that allow pathogens to bind to host cells

Question 30

Specific immune response: what two types of antibodies are there?

Answer 30

1. Membrane-bound antibodies = attached to the membrane of a B cell
2. Secreted antibodies = free from any attachment

Question 31

Specific immune response: how do the two types of antibodies vary in structure?

Answer 31

They have different heavy chain proteins, membrane-bound antibodies have an extra section that anchors them to B cell membrane

Question 32

Specific immune response: what codes for two heavy chain proteins in an antibody?

Answer 32

Both heavy chain proteins are coded for by a single gene

Question 33

Why is the primary response slow?

Answer 33

There are few B cells that can make the antibody needed to bind to the specific antigen

Question 34

Immunity: what do T memory cells remember + what do they divide into?

Answer 34

T memory cells remember the specific antigen and will recognise it the second time around
They divide into the correct type of T cells to kill the cell carrying the antigen

Question 35

Immunity: what do B memory cells remember? + what do they divide into?

Answer 35

They remember the specific antibodies needed to bind to the antigen
They divide into plasma cells that produce the right antibody to the antigen

Question 36

What does it mean if a person is immune?

Answer 36

Their immune system can respond quickly to a second infection using a quick secondary response

Question 37

What are the two types of immunity?

Answer 37

• Active immunity

- Passive Immunity

Question 38

What is active immunity?

Answer 38

Immunity you get when your immune system makes its own antibodies after being stimulated by an antigen

Question 39

What are the two types of active immunity?

Answer 39

• Natural = become immune after catching a disease

- Artificial = become immune after a vaccine

Question 40

Active immunity: how do vaccines work?

Answer 40

They contain antigens that stimulate the primary immune response against a particular pathogen without causing disease = produces memory cells

Question 41

What is passive immunity?

Answer 41

Immunity you get from being given antibodies from a different organism

Question 42

What are the two types of passive immunity?

Answer 42

• Natural = when a baby becomes immune due to the antibodies it receives from its mother via placenta and breast milk
• Artificial = when you become immune after being injected by antibodies eg tetanus

Question 43

What is the evolutionary race between humans and pathogens?

Answer 43

Over millions of years humans have evolved better immune systems whilst at the same time pathogens have evolved better ways to evade their hosts immune system

Question 44

Describe HIVs evasion mechanisms that support the theory of an evolutionary arms race:

Answer 44

• HIV kills the immune system cells it infects which reduced overall number of immune cells which reduces its chance of being detected
• HIV has a high mutation rate in genes that code for antigen proteins which forms new strains = antigenic variation so immune system must produce a primary response for each new strain
• HIV disrupts antigen presentation in infected cells which prevents immune cells recognising and killing them

Question 45

Describe mycobacterium tuberculosis’ evasion mechanisms that support the theory of an evolutionary arms race:

Answer 45

• M. tuberculosis produces chemicals that prevent the lysozyme fusing with the phagocytic vacuole when they are engulfed by pathogens so bacteria isn’t broken down and can multiply
• M. tuberculosis disrupts antigen presentation so immune cells can detect and kill infected phagocytes

Question 46

Specific immune response: describe how antibodies neutralise toxins

Answer 46

Antibodies can bind to toxins produced by pathogens which prevents human cells being affected – toxin-antibody complexes are phagocytosed