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Immunity
Defence mechanisms
Non specific
Immediate response
Same for all pathogens
Physical
Barrier
e.g. Skin
phagocytosis
Specific
slower response
specific to each pathogen
cell-mediated humoral
response
response
T lymphocytes B lymphocytes
Phagocytosis
1. Chemical products from a pathogen attract
phagocytes.
2. Phagocytes attach themselves to the surface
of the pathogen.
3. They engulf the pathogen forming a vesicle
called a phagosome.
4. Lysosomes move towards the phagosome
and fuse with it.
5. Enzymes found in the lysosomes break down
the pathogen by hydrolysis.
6. Products of this breakdown are absorbed
into the cytoplasm of the phagocyte.
Antigens
An antigen is any part of an organism or
substance that is recognised as non-self by the
immune system and stimulates an immune
response.
For example – proteins that are part of the cell
membrane or cell wall of invading cells such as
microorganisms.
The presence of an antigen triggers the production
of an antibody.
T lymphocytes
T lymphocytes respond to an organism’s own
cells that have been invaded by non-self
material e.g. a virus or a cancer cell.
These cells present antigens on their cell
membrane.
T lymphocytes respond to this – Cell Mediated
Immunity.
Response of T lymphocytes
1. Once T cells have been activated they divide
rapidly by .................... to form a ................
2. They develop into .................. cells that
enable a rapid response to future infections
by the same pathogen.
3. They stimulate ....................to engulf
pathogens.
4. ................T cells stimulate ...............to divide.
5. ...................T cells kill infected cells.
Antibodies
B cells
1. Type of immunity = ......................immunity
2. B cells present antigens from pathogen on
their surface.
3. They are activated by ................... cells.
4. Plasma cells secrete .................. directly –
primary immune response.
5. ............... cells provide long term immunity.
Vaccination
Active immunity – stimulates production of
antibodies by individuals’ own immune system.
Vaccination – introduction of a substance into the
body with the intention of stimulating active
immunity.
Why is vaccination not always successful in
eliminating a disease?