Transcript Third Line Immunity

Third Line of Defence
• Aims:
• Must be able to state the substances involved in
the third line of immunity.
• Should be able to describe the production and
differentiation of B and T cells.
• Could be able to outline the role of B and T
cells.
The Third Line of Defense
• Specific resistance is a third line of
defense.
The 2nd line of defense
The 3rd line of defense
• Forms the immune response and
targets specific pathogens.
• Specialized cells of the immune
system, called lymphocytes are:
– B-cells: produce specific proteins
called antibodies, which are
produced against specific
antigens.
B cell:
Antibody
production
Lymphocytes
T cell:
Cell-mediated
immunity
– T-cells: target pathogens directly.
2
Third Line of Defense
•
There are two main components of the vertebrate immune
system:
•
The humoral immune system involves the action of B-cells,
which produce antibodies. The humoral system is associated
with serum, the non-cellular part of the blood.
•
The cell-mediated immune system is associated with the
production of specialized lymphocytes called T-cells.
•
The humoral and cell-mediated systems work separately
and together to protect us from disease.
Cells of the Third Line of Defense
•
Two main groups of lymphocytes are involved in
specific immunity.
•
All lymphocytes are produced in the bone marrow.
1. Mature in the bone marrow - B lymphocytes or B
cells.
2. Mature in thymus gland - T lymphocytes or T
cells.
•
There are different kinds of B and T cells…
Mast Cell
- Secretes
hisatmines
phagocytes
Distinguishing Self
• Achieved through the Major Histocompatibility Complex
(MHC).
• The MHC = cluster of tightly linked genes on chromosome 6 in
humans.
• Genes code for protein molecules (MHC antigens) attached to
the surface of body cells.
• The MHC antigens are used by the immune system to
recognise its own and foreign material.
• Class I MHC antigens located on surface of all human cells.
• Class II MHC antigens restricted to macrophages and B-cells.
Antigens
•
Antigens = foreign substances that cause formation of
antibodies.
•
Antigens include:
– Potentially damaging microbes and their toxins.
– Substances such as pollen and flea and dust mite feces.
– Blood cell surface proteins.
– The surface proteins of transplanted tissues and organs.
B–Cells
• B-cells (B-lymphocytes) originate and mature in the bone
marrow of the long bones (e.g. the femur).
• Migrate from the bone marrow to the lymphatic organs.
• B-cells defend against:
– Bacteria and viruses outside the cell
– Toxins produced by bacteria (free antigens)
• Each B-cell can produce antibodies against only one specific
antigen.
• A mature B-cell may carry up to 100 000 antibody molecules
embedded in its surface membrane.
B-Cells
• Each B-Cell only has one type of antibody…
• The body needs to defend itself against millions of antigens.
• Only a small number of each corresponding antibody.
• The type of antibody is genetically predetermined.
• Having a small number of each antibody type means, more
chance of ‘recognising’ the antigen.
Humoral Immunity
Other B-cells
recognize
different antigens
Surface antigen
The humoral response begins
when a foreign protein (antigen)
activates a particular B-cell.
Recognition
B-cell
The particular B-cells multiply,
to form many plasma cells.
Plasma cells make antibodies
specifically designed to attack
and kill the identified pathogen.
Some B-cells differentiate into
long lived memory cells.
These memory cells will rapidly
produce antibodies if the same
pathogen enters the body again.
Pathogen
Plasma cells
Second Exposure
Antibodies
Original
B-cell
B–Cell Differentiation
• B-cells differentiate into two kinds of
cells:
Memory cell
• Memory cells:
When these encounter the same
antigen again (even years or decades
after the initial infection), they rapidly
differentiate into antibody-producing
plasma cells.
• Plasma cells:
These secrete antibodies against
antigens. Each plasma cell lives for
only a few days, but can produce
about 2000 antibody molecules per
second.
Antibody
Plasma cell
After the Antigen has Attached to an
Immunoglobulin…
• The selected B-Cell then needs to reproduce rapidly so that
there is a large number of identical cells that can respond to
the antigen.
• This is called clonal expansion.
• Cells cloned in this way have exactly the same genetic
material and immunoglobulins.
• Most of these cells will then differentiate into plasma cells…
Antigens and Antibodies
Molecular
model
• Antibodies
(immunoglobulins)
are proteins made in
response to antigens.
– Antibodies
recognize and bind
to antigens.
– Antibodies are
highly specific and
can help destroy
antigens.
– Each antibody has
at least two sites
that can bind to an
antigen.
Symbolic
model
Antibody
One of the two
binding sites on the
antibody
Antigen
Antibody Structure
16
Immunoglobulins
• Although there are over 10 million different types of
immunoglobulins in our bodies, they exist in several
classes:
• IgM antibodies are usually the first to be secreted –
cause an agglutination of antigens (makes easier for
phagocytes).
• IgG activate complement proteins,neutralise toxins
directly.
• IgA neutralise pathogens in the digestive, respiratory
and reproductive tracts.
• IgE help initiate inflammation after infection.
17
Inactivation of Antigens
Neutralization
Clumping
particulate antigens
Precipitation of
soluble antigens
Antibodies
Antibody
Virus
Bacterial cell
Soluble
antigens
Toxin
Antibodies bind to viral
binding sites and coat
bacterial toxins.
Soluble antigens are
stuck together to form
precipitates.
Solid antigens such as
bacteria are stuck
together in clumps.
Enhances Phagocytosis
Macrophage
Bacteria
Inactivation of Antigens
Activation of complement
Complement
Bacterial cell
Tags foreign cells for destruction by
phagocytes.
Enhances phagocytosis
Enhances inflammation
Leads to rupture of cell
Blood
vessel
Lesion
Macrophage
Macrophage
Bacteria
Bacteria
Bacterial cell
Activity
• Complete the activities on pages 155 and
156 in Biozone book.
T-Cells
• T-cells originate from stem cells and mature after
passing through the thymus gland.
• They respond only to antigenic fragments that
have been processed and presented bound to the
MHC by infected cells or macrophages
(phagocytic cells).
• T-cells defend against:
– Intracellular bacteria and viruses.
– Protozoa, fungi, flatworms, and roundworms.
– Cancerous cells and transplanted foreign
tissue.
T-Cell Differentiation
•
T-cells can differentiate into four specialized
types of cell:
– Helper T-cell
•Activates cytotoxic T cells and
other helper T cells.
•Necessary for B-cell activation.
– Suppressor T-cell
•Regulates immune response by turning it
off when no more antigen is present.
– T-cell for delayed hypersensitivity
•Causes inflammation in allergic reactions
and rejection of tissue transplants.
– Cytotoxic (Killer) T-cell
•Destroys target cells on contact.
Cell Mediated Immunity
Antigens, such as
those produced by
abnormal cells, are
identified by and
activate specific killer
T-cells.
Killer T-cells
Antigen
produced by
abnormal cell
Recognitio
n
Helper T-cell
Note: HIV (the AIDS virus) disrupts
the cellular immune system by
destroying helper T-cells.
The killer T-cells attach to
and destroy the abnormal
cell. Killer T-cells remain as
memory cells to quickly
attack any abnormal cells
that reappear.
With the assistance of
helper T-cells the killer
T-cells begin to
multiply.
Activity
• Complete the activities on pages 153 in
Biozone book.