H 3.5.7 Human Immune System [E.S.]
Objectives – What you will need to
know from this section
The Immune System
 Role of lymphocytesB and T cell types.
 Role of B cells in antibody production.
 Role of T cells as helpers, killers, suppressors, and
memory T cells.
 B cells produce antibodies.
 Each B cell produces just one type of antibody.
 T cells act in one of four
processes:
as helper T cells which recognise antigens,
and stimulate the production of B cells
as killer T cells which attack cells containing a
foreign antigen,
as suppressor T cells which stop immune
responses
as memory T cells which can memorise the
immunity.
Human Immune System [E.S.]
 The human body is designed to protect itself from foreign cells
or invaders, and we have two lines of defence -- general and
specific.
 Our Specific Defence System involves an antigen-antibody
response, involving lymphocytes and monocytes.
LYMPHATIC SYSTEM
1. Drainage – returns
leaked fluid to the blood.
2.
Transport – lipids
(fats) are absorbed from the
small intestine and carried to
the skin or other organs for
storage.
3.
Defence – filters
blood. Germs that invade the
body will enter the blood or
tissue fluid and eventually
get filtered through the
lymph and lymph nodes,
where white cells attack and
destroy them.
 Our Specific Defence System involves :
 an antigen-antibody response, involving speciliased
white blood cells, called lymphocytes and monocytes
[macrophages].
1. Lymphocytes - Stored in lymphatic system (spleen, lymph
nodes, tonsils, adenoids & thymus gland), have large
nucleus and make antibodies. (25% of white cells)
lymphocyte
2. Monocytes – digest bacteria, have kidney shaped
nucleus & live for 6-9 days (5% of white cells)
Monocytes -- [Macrophages]
 Monocytes are phagocytic white blood
cells – also called macrophages
 These engulf bacteria and viruses upon
contact.
Monocyte
Germ
“Eating”
germ
 Others secrete chemicals that stimulate general
defence and cause fever to destroy microbes at high
temperatures.
Monocyte engulfs
an invader
Monocyte engulfs a
bacterium
LEARNING CHECK
• What is meant by a “specific defence
system”?
• Name two types of White cell involved in
this system.
• What is a lymphocyte?
• What is a Monocyte?
• What does “engulf” mean?
• Can you name an animals that engulfs its
prey?
 Antigens are any foreign
molecules capable of
triggering an antibody
response.
Germ
(antigen)
 An antibody is a protein, made by a
lymphocyte, which sticks to an
antigen and marks it for destruction
by other defence cells [monocytes].
Antibody
monocyte
“Eating
” germ
 Antigens may be found in bacterial cell walls, viral coats,
foreign cells or produced in cancerous cells.
 Lymphocytes are made in the bone marrow and then move to
the lymph nodes before or soon after birth.
 Monocytes engulf an invader, digest it and then display some
of the invader’s antigen on its own cell membrane.
 Body cells do the same
with viruses that get into
them.
 Lymphocytes are continually inspecting monocytes and body
cells for evidence of ‘foreign’ antigen.
 When detected, the lymphocytes are stimulated to divide into
huge numbers of cells.
THE IMMUNE
RESPONSE
T lymphocytes
 They attack cells that
have invading antigen on
their cell membrane.
 T cells do not produce
antibodies.
 Instead they act as
 helper T cells
 recognise antigens, enlarge, and secrete chemicals
such as interferon that stimulate production of B
cells
 killer T cells
 attack cells containing a foreign antigen,
 secrete a chemical called perforin that perforates the
membranes of cells ;
 destroy virus-infected cells, tumour cells and
transplant tissue.
 suppressor T cells
 stop the immune response after the
pathogen has been destroyed.
 memory T cells
 Memory cells that form during the first response to
an antigen do not engage in that first battle.
 They circulate in the body for years, and can
intercept antigens far quicker.
 So they memorise the immunity, even for life.
LEARNING CHECK
• Distinguish between antigen and antibody.
• Distinguish between lymphocyte and
monocyte.
• What is the thymus gland?
• Name 4 types of T-lymphocyte and a
function of each.
• Distinguish between interferon and perforin.
B lymphocytes
 B lymphocytes mature in
the bone, before moving
to the lymph nodes,
where they acquire their
receptor molecules.
 B lymphocytes attack
antigens in the blood or
body fluids, by producing
antibodies that surround
them.
 When a B cell encounters
matching antigen, they
divide into plasma and
memory cells.
 The plasma cells produce
antibody molecules, that bind
to pathogens and toxins that
are circulating in tissues or
body fluids, and mark them
for destruction by monocytes.
 Each B cell produces just
one type of antibody.
 Memory B and T cells that form during the first response to an
antigen, do not engage in that first battle.
 They circulate in the body for years, and can intercept antigens
far quicker.
 This is how we achieve immunity against many diseases –
either by getting the disease once or by preventing them using
vaccines.
Monocyte
Monocyte
LEARNING CHECK
•
•
•
•
•
What are B-lymphocytes?
What is an activated B-lymphocyte?
What is a plasma cell?
Explain why antibodies are specific.
Explain why vaccination gives us long term
immunity.