Slides in this set
THE IMMUNE RESPONSE
Antigens are molecules (usually proteins) that can generate an immune response
when detected by the body. They are usually found on the surface of cells and are
used in the immune system to identify: pathogens (organisms that cause disease),
abnormal body cell (e.g. cancerous or pathogen- infected cells, which have
abnormal antigens on the surface), toxins and cells from other individuals of the
same species (e.g. organ transplants).
There are four main stages in the immune response:…read more
A phagocyte (e.g. macrophage) is a type of white blood cell that carries out
phagocytosis (engulfment of pathogens). They're found in the blood and in
PHAGOCYTOSIS tissues and are the first cells to respond to an immune system trigger
inside the body.
A phagocytes recognises the foreign antigens on a pathogen. The membrane of the
phagocyte then projects out and the cytoplasm of the phagocyte moves round the
pathogen (engulfing it) as it is enclosed in a phagocytic vacuole.
The lysosomes (contain the enzymes lysozymes) fuse with the phagocytic vacuole and
release enzymes into the vacuole. The enzymes breakdown the pathogen. The phagocyte
then presents the pathogen's antigens it sticks the antigens on its surface to activate
other immune system cells.
1) The bacteria will be 2) Phagocytosis. The 3) Lysosomes (vesicles containing 5) Now the bacteria will be The lymphocytes will also kill
attracted to the membrane neutrophil will engulf the digestive enzymes) will fuse with killed and digested by bacteria. However, some
of the neutrophil. bacteria. the phagosome containing the enzymes. bacteria may escape by having a
bacteria. protective cell wall or capsule.…read more
PHAGOCYTES ACTIVATE T-CELLS
A T-cell (also called a T-lymphocyte) is another type of white blood cell. It has
receptor proteins on its surface that bind to complementary antigens presented to
it by phagocytes. This activates the T-cell. Different types of T-cells respond in
different ways. For example, helper T-cells (TH cells) release chemical signals that
activate and stimulate phagocytes and cytotoxic T-cells (TC cells), which kill abnormal and
foreign cells. TH cells also activate B-cells which secrete antibodies.…read more
B-cells (also called B-lymphocytes) are also a type of white blood cell. They're
covered with antibodies proteins that bind antigens to form an antigen-antibody
complex. Each B-cell has a different shaped antibody on its membrane, so different
ones bind to different shaped antigens.
When the antibody on the surface of a B-cell meets a complementary shaped
antigen, it binds to it. This, together with the substance released from helper
T-cells, activates the B-cell. This process is called clonal selection. The activated
B-cell divides into plasma cells.…read more
Plasma cells are identical to B-cells (they're clones). They secrete loads of antibodies
specific to the antigen. These are called monoclonal antibodies. They bind to the
antigens on the surface of the pathogen to form lots of antigen-antibody complexes.
An antibody has two binding sites, so can
bind to two pathogens at the same time.
This means that pathogens become clumped
together this is called agglutination.
Phagocytes then bind to the antibodies and
phagocytose many pathogens at once. This
process leads to the destruction of
pathogens carrying this antigen in the body.…read more