Chapter 11: Immunity

Question 1

Define the term phagocyte.

Answer 1

Specialised white blood cells that engulf and
destroy pathogens. There are two types:
neutrophils and macrophages.

Question 2

State where phagocytes are produced.

Answer 2

Bone marrow

Question 3

Define the term phagocytosis.

Answer 3

The process by which phagocytes engulf

and destroy pathogens.

Question 4

Outline the process of phagocytosis.

Answer 4

1. Phagocyte moves towards pathogen via chemotaxis
2. Phagocyte engulfs pathogen via endocytosis to form a phagosome
3. Phagosome fuses with lysosome forming a phagolysosome
4. Lysozymes digest pathogen
5. Products of pathogen hydrolysis absorbed by the phagocyte or
   released into the cytoplasm

Question 5

Define the term immune response.

Answer 5

The body’s response to ‘non-self’ antigens. It
consists of a non-specific phase involving
neutrophils and macrophages, and a specific
phase involving T and B lymphocytes.

Question 6

What is an antigen?

Answer 6

A chemical present on the surface of a cell

that induces an immune response.

Question 7

What are antigen presenting cells (APCs)?

Answer 7

Any type of immune cell which displays
parts of a pathogen (antigens) on its
surface to elicit an immune response.

Question 8

What is meant by the term self-antigen?

Answer 8

Antigens present on an organism’s cells
that are tolerated by their own immune
system. They induce antibody formation
in other organisms.

Question 9

What is meant by the term non-self antigen?

Answer 9

Foreign antigens that originate from
outside the body and induce an immune
response.

Question 10

Describe the structure and function of T

lymphocytes.

Answer 10

● Mature in the thymus gland

● Many specific receptors and immunoglobulins on surface

● Four main types of T lymphocyte:

  ○  T helper - bind to antigens on antigen-presenting cells and secrete interleukins
  ○  T killer - secrete perforin, destroying pathogens with a specific antigen
  ○  T memory - provide immunological memory
  ○  T regulatory - suppress other immune cells to prevent autoimmune disease

Question 11

Describe the structure and function of B

lymphocytes.

Answer 11

● Mature in the bone marrow

● Many specific receptors and immunoglobulins on surface

● Three main types of B lymphocyte:

○  Plasma cells - produces antibodies specific to a particular pathogen
○  B effector - divides to form plasma cells
○  B memory - provide immunological memory

Question 12

Define the humoral immune response.

Answer 12

Immunity regulated specifically by the
production of antibodies. Associated with
B lymphocytes.

Question 13

State the role of plasma cells.

Answer 13

Production of antibodies specific to a

particular pathogen.

Question 14

Outline the process of the cell-mediated response.

Answer 14

Complementary T helper lymphocytes bind to foreign antigens on
antigen-presenting cell. T cells undergo clonal expansion.
Four main types of T lymphocytes produced:

● T effector cells
● T killer
● T helper cells
● T memory cells

Question 15

Outline the process of the humoral response.

Answer 15

1. Complementary T helper lymphocytes bind to foreign antigens on
   antigen-presenting T cells
2. Cytokines released that stimulate the clonal expansion of
   complementary B lymphocytes
3. B lymphocytes differentiate into plasma cells
4. Plasma cells secrete antibodies with complementary variable region
   to antigen. Antibodies destroy the pathogen

Question 16

State the potential impact of Leukemia on blood cell

count and its consequence.

Answer 16

May cause uncontrolled division of bone marrow stem
cells, increasing the number of red and white blood
cells in the bloodstream. Leukaemia cells are typically
immature and can disrupt the blood clotting cascade
and specific immune responses.

Question 17

State the effect of bacterial infection on T lymphocyte

count.

Answer 17

T lymphocyte count increases due to the
cell-mediated immune response.
A greater number of T cells will circulate the
body even after the infection has subsided.

Question 18

State the effect of HIV on T cell count.

Answer 18

HIV destroys specific T cells. A decrease
in normal levels of T cells is expected
over time in individuals with HIV.

Question 19

Compare the primary and secondary immune

responses.

Answer 19

● Primary immune response - initial response when a pathogen is
first encountered. A small number of antibodies are produced
slowly.

● Secondary immune response - pathogen encountered for a
second (third, fourth…etc.) time. Immunological memory gives a
rapid production of a large number of antibodies.

Question 20

What is the function of memory cells?

Answer 20

They remain in the body for a long time following
an infection and provide long-term immunity. If
the organism encounters the same pathogen in
the future, they can divide rapidly to provide an
effective secondary immune response.

Question 21

Define the term autoimmune disease.

Answer 21

A condition in which the immune system fails
to distinguish between self and non-self
antigens, so attacks and destroys healthy
body tissue. Examples include arthritis and
lupus.

Question 22

How does autoimmune disease occur?

Answer 22

T cells with self antigens are not destroyed
during the maturation process. If these cells
become active they will launch an immune
response on self cells, leading to cell
damage.

Question 23

What is myasthenia gravis?

Answer 23

An autoimmune disease that causes skeletal muscle
weakness due to the production of antibodies which
damage nicotinic acetylcholine receptors at the
neuromuscular junction. Motor neurons cannot be
stimulated therefore muscles receive no impulses. This
leads to atrophy of muscles.

Question 24

Describe the structure of an antibody

Answer 24

● Y-shaped. Two ‘light chains’ bonded to two
longer ‘heavy chains’ by disulfide bridges

● Binding sites on variable region of light
chains have specific tertiary structure
complementary to an antigen

● The rest of the molecule is known as the
constant region

Question 25

How do antibodies destroy pathogens?

Answer 25

● Agglutinins form antigen-antibody complexes to enhance phagocytosis
(pathogens clump, engulfing occurs more efficiently)

● Bind to foreign cells and attract ‘complement’, a collection of proteins which
form pores in the cell surface membrane of pathogens, destroying them

● Opsonins mark microbes for phagocytosis

● Antitoxins make toxins insoluble via precipitation/neutralisation

Question 26

Outline the “hybridoma method”

Answer 26

An antigen is injected into a mammal to stimulate
clonal expansion of complementary B cells. These
B cells are harvested and fused with a myeloma,
which can undergo mitosis an indefinite number of
times. The hybrid cell line is called a hybridoma.

Question 27

How can monoclonal antibodies (MAs) be used in

diagnosis?

Answer 27

MAs for specific antigens can be attached to
radioactive markers, allowing for specific cells or
proteins to be found in the body (e.g. cancer
cells, fibrin fibers to locate blood clot). Also useful
in blood typing and tissue matching.

Question 28

How can monoclonal antibodies (MAs) be used in

treatment?

Answer 28

Can bind to certain cells, marking them
for destruction. Useful in treatment of
cancers and autoimmune diseases.

Question 29

State an issue with using monoclonal antibodies

(MAs) in treatment and how it is overcome.

Answer 29

MAs require multiple treatment rounds. As they are
sourced from animals this may trigger an immune
response. To overcome this MAs are ‘humanised’
by altering the amino acid sequence to those found
within humans.

Question 30

Compare and contrast passive and active immunity.

Answer 30

Passive Active

              Both involve antibodies (natural or artificial source)

No memory cells and antibodies not replaced Memory cells produced - long-term
when broken down - short-term

           Immediate                                Time lag

  Antibodies from external source        Lymphocytes produce antibodies

No direct contact with antigen necessary Needs direct contact with antigen

Question 31

Give examples of passive and active immunity.

Answer 31

● Passive natural - antibodies in colostrum or transferred
across placenta

● Passive artificial - anti-venom, needle stick injections

● Active natural - humoral response to infection

● Active artificial - vaccination

Question 32

Define vaccination.

Answer 32

The deliberate exposure of an individual to
antigens from a pathogen to provide
artificial active immunity.

Question 33

How do vaccinations that use antigens provide

long-lasting immunity?

Answer 33

● Antigens in vaccine trigger primary immune
response without infection
● If pathogen is encountered, secondary immune
response destroys the pathogen before symptoms
develop

Question 34

How do vaccinations that use antibodies provide

short-term immunity?

Answer 34

● Antibodies give rapid protection against a harmful
microorganism

● Allows time for the development of an active
immune response

Question 35

How can vaccination programmes control the spread

of infectious disease?

Answer 35

Herd immunity - significant proportion of population is vaccinated so pathogen is less
likely to affect a non-immunised individual. Disease cannot spread in immune
individuals.

Ring vaccination - all individuals within a radius of a known case are immunised,
preventing spread from localised areas.

Boosters - where a vaccine does not induce a strong response, these maintain
immunity.