6.3 The body's response to infection

Question 1

Immune response

Answer 1

The way in which the
immune system of the body reacts to an
invading pathogen.

Question 2

Immune system

Answer 2

The immune system is the
collection of all the body’s parts that help protect
us from disease. It includes tissues (e.g. skin),
cells (e.g. lymphocytes) and enzymes (e.g.
lysozyme).

Question 3

Non-specific immune response

Answer 3

The body’s
general response to any invading pathogen. It
includes the inflammatory response which
takes place at a wound in response to the
production of substances such as histamine. It
also includes phagocytosis in which invading
pathogens and cell debris are engulfed and
destroyed by neutrophils and macrophages.

Question 4

Specific immune response

Answer 4

The reactions of B
cells and T cells, types of lymphocyte, to
particular antigens form the specific immune
response. Specific immunity is always directed
at a particular pathogen. When a B cell comes
into contact with a specific antigen, it binds to
the antigen and starts to divide. As a result of
this cell division it produces plasma cells which
secrete antibodies specific to the antigen. It also
produces memory cells. Memory cells are
longer lived and can respond quickly to
exposure to the same antigen.

Question 5

Lysozyme

Answer 5

An enzyme found in tears, saliva and
other secretions which kills bacteria by
breaking down their cell walls.

Question 6

Inflammatory response, Inflammation

Answer 6

The
characteristic reddening and swelling around a
wound. A substance called histamine produced
at the site of the wound is responsible for
inflammation. Histamine produces dilation of
arterioles in the area, leading to increased blood
flow in the capillaries. It also causes blood
vessels to become more permeable. As a result
plasma, white blood cells and antibodies leak
from the blood into the nearby tissue and
produce swelling.

Question 7

Histamine

Answer 7

A substance produced at the site of a
wound by damaged white blood cells and mast
cells found in the connective tissue below the
skin and around blood vessels. Histamine is
responsible for inflammation following a
wound. The characteristic reddening is caused
by dilation of arterioles in the area leading to
increased blood flow in the capillaries.
Histamine is also released in large amounts in
allergic reactions.

Question 8

Oedema

Answer 8

Swelling caused by the accumulation of
tissue fluid. For instance, tissue fluid is formed
at the arteriole end of a capillary. It filters back
into the venule end of the capillary. Excess
tissue fluid is normally returned to the blood
system via the lymphatic system. Oedema
results when more tissue fluid is formed than is
returned either through the venule end of the
capillary or through the lymphatic system. There
are various causes of oedema, including high
blood pressure, starvation and blocked lymph
vessels.

Question 9

Phagocyte, Phagocytosis

Answer 9

Phagocytes are white
blood cells that engulf and destroy bacteria and
cell debris in a process called phagocytosis.
They include both neutrophils and
macrophages. Phagocytes form part of the
body’s immune response.

Question 10

Neutrophil

Answer 10

A type of white blood cell that forms
part of the immune system of the body.
Neutrophils are able to leave blood capillaries by
squeezing between the cells of the capillary
walls. They remove bacteria from the body by
engulfing and destroying them in a process
called phagocytosis.

Question 11

Macrophage

Answer 11

A type of large white blood cell
that forms part of the immune system of the
body. Some macrophages are able to move
round the body and collect near a site of
infection. They remove bacteria from the body
by engulfing and destroying them in a process
called phagocytosis.

Question 12

Lymphocyte

Answer 12

A type of white blood cell which
has a large nucleus and a small amount of
cytoplasm. Lymphocytes are part of the
immune system of the body. There are several
types of lymphocyte: macrophages,
neutrophils, B cells and T cells.

Question 13

Lymph nodes

Answer 13

Part of the lymphatic system
which acts as a filter. As lymph passes through
the node, any pathogens present activate
lymphocytes and macrophages which then
destroy the microorganisms.

Question 14

Interferon

Answer 14

A substance produced by the cells of a
mammal when they are attacked by a virus.
They protect other cells from infection by
inhibiting the synthesis of viral proteins.

Question 15

T cell

Answer 15

A type of lymphocyte cell which forms
part of the immune system. A T cell is also
known as a T lymphocyte and gets its name
because it matures in the thymus gland. There
are two types of T cell. T killer cells destroy
foreign cells that may enter the body. They also
destroy cells infected by pathogens. T helper
cells stimulate B cells and T killer cells to
divide.

Question 16

B cell, B lymphocyte

Answer 16

A cell which forms part of
the immune system. A B cell is also known as a
B lymphocyte. When it comes into contact with
a particular antigen, it binds to the antigen and
starts to divide. Cell division is stimulated by
cytokines released by a T helper cell, which
also binds to the B cell. As a result of this cell
division it produces plasma cells which secrete
antibodies. It also produces memory cells.
Memory cells are longer lived and can respond
quickly to exposure to the same antigen.

Question 17

Antibody, Antibodies

Answer 17

There are several different
types of white blood cell. One of these is the
lymphocyte. An antibody is a molecule
produced by a B lymphocyte cell when it
encounters a particular antigen. For example,
the virus that causes measles has antigens on its
surface. If a person gets measles, these antigens
cause the lymphocytes to produce measles
antibodies. The antibodies help the person to
overcome the infection and recover.

Question 18

Immunoglobulins

Answer 18

The type of protein towhich

antibodies belong.

Question 19

T helper cell, T memory cell

Answer 19

A cell which forms
part of the immune system. T helper cells
stimulate B cells and T killer cells, other types
of lymphocyte, to divide. The B cells divide to
produce plasma cells which secrete antibodies.
T killer cells destroy foreign cells that may enter
the body. They also destroy cells infected by
pathogens. T helper cells also enhance the
activity of phagocytes. Once activated, a
T helper cell divides to produce a clone of
T helper cells and a clone of T memory cells
which allow the body to respond quickly if
infected with the same antigen.

Question 20

T killer cell

Answer 20

A cell that forms part of the immune
system. T killer cells destroy pathogen-infected
cells. They also attack other foreign cells that
enter the body.

Question 21

Antigen-presenting cell, APC

Answer 21

Foreign cells have
protein molecules on their surface which form
antigens. When foreign cells are introduced into
the body, they are engulfed by lymphocytes.
The lymphocyte becomes an antigen-presenting
cell. The antigens are carried to the surface of
the lymphocyte and act as a signal, triggering the
immune system.

Question 22

Cytokines

Answer 22

Chemicals released by activated
T helper cells. Cytokines stimulate division and
differentiation of the B and T cells in the
immune response.

Question 23

B effector cell

Answer 23

Division of B cells as part of the
immune response produces B effector cells and
B memory cells. B effector cells differentiate to
produce plasma cells that release antibodies
into the blood and lymph. B effector cells are
relatively short-lived, lasting only a few days.

Question 24

B memory cell

Answer 24

Division of B cells as part of the
immune response produces B effector cells and
B memory cells. B memory cells remain in the
circulation for months or years and can respond
quickly to exposure to the same antigen that
resulted in their original production.

Question 25

Plasma cell

Answer 25

One of the cell types formed when a
B cell detects an antigen. The B cell divides by
mitosis to produce a clone of plasma cells which
secrete antibodies into the blood. Plasma cells
are relatively short-lived and only survive for a
few days.

Question 26

Clonal selection

Answer 26

The division of a particular
B cell in the primary immune response as a
result of an antigen binding to the B cell with a
complementary receptor. Two clones of B cells
are formed: B effector cells and B memory cells.
All the cells produced have the receptor
complementary to the antigen.

Question 27

Primary immune response

Answer 27

The process by
which antibody-producing cells are produced by
the immune system. This occurs when B cells
come into contact with a particular antigen and
produce a clone of plasma cells which secrete
antibodies specific to the antigen concerned.
Memory cells are also created that will take part
in the secondary immune response if the
antigen is encountered in the future

Question 28

Secondary immune response

Answer 28

The process that
occurs when memory cells in the immune
system come into contact with the particular
antigen that triggered their production in the
primary immune response. The secondary
immune response is faster than the primary
immune response. There is a greater production
of antibodies and the response lasts longer. The
bacteria or viruses concerned are destroyed so
rapidly that symptoms may not develop.

Question 29

Immune

Answer 29

A person who is immune to a particular
disease is able to destroy the relevant pathogen
quickly, thus preventing the onset of symptoms.
Prior exposure to the disease or vaccination
against it causes the B cells and T cells to
produce memory cells. These memory cells
provide lasting protection against the disease
concerned.

Question 30

Apoptosis

Answer 30

The process in which healthy animal
cells die during the normal development of an
organism. For example, there are millions of
cells in the brain of a human embryo. During
development apoptosis results in many of these
cells dying even though they are quite healthy.
The result of the death of these cells is the
pattern of cells found in the adult brain.