Immunity
Natural Barriers to pathogen entry
Outer protective covering (skin)
Enzyme lysozyme- in tears, saliva and sweat
Epithelial lining covered in mucus e.g. respiratory tract. Mucus traps pathogens and prevents
them penetrating underlying membranes. Cilia sweep mucus and its trapped pathogens back
up the trachea.
HCl in the stomach
Phagocytosis
Inflammatory response, capillaries in the infected region become leaky, allowing plasma to seep into
the surrounding areas. Inflamed parts of the body become swollen with phagocytes, dead pathogens
and cell debris, collectively known as pus. Inflamed regions become red due to increased blood flow.
1. The phagocyte moves towards the pathogen, attracted by the chemicals it produces
2. As it does so the phagocyte membrane invaginates to begin to enclose the pathogen
3. As the pathogen is engulfed, the invaginated phagocyte membrane forms a vesicle
(phagosome) around the pathogen
4. Lysosomes move towards the phagosome and fuse with it
5. Hydrolytic enzymes within the lysosomes are released into the phagosome, onto the
pathogen. These enzymes hydrolyse the pathogen.
6. The soluble digested products are absorbed into the cytoplasm of the phagocyte.
All of the above is the non-specific response
Specific Immune Response
Antigens are recognised as foreign. Different pathogens have different antigens causing immune
response to be specific. Lymphocyte having a receptor on its cell surface membrane that is
complementary in shape to the antigen.
Self and non self: In the foetus, lymphocytes make contact with other ‘self’ cells. Lymphocytes that
are complementary in shape with foetal cells are switched off. By the time the baby is born the
functional lymphocytes that remain are those that are not complementary to self-cells.
Types of lymphocyte:
Type Where formed Site of Name of immune Nature of
development response immune
response
B-lymphocyte Stem cells in bone Bone marrow Antibody-mediated Produce antibodies
marrow which responds to
antigens found in
body fluids. Usually
viral or bacterial.
T-lymphocyte Stem cells in bone Thymus gland Cell-mediated Respond to
marrow antigens attached
to body cells.
Usually viral
infection.
Natural Barriers to pathogen entry
Outer protective covering (skin)
Enzyme lysozyme- in tears, saliva and sweat
Epithelial lining covered in mucus e.g. respiratory tract. Mucus traps pathogens and prevents
them penetrating underlying membranes. Cilia sweep mucus and its trapped pathogens back
up the trachea.
HCl in the stomach
Phagocytosis
Inflammatory response, capillaries in the infected region become leaky, allowing plasma to seep into
the surrounding areas. Inflamed parts of the body become swollen with phagocytes, dead pathogens
and cell debris, collectively known as pus. Inflamed regions become red due to increased blood flow.
1. The phagocyte moves towards the pathogen, attracted by the chemicals it produces
2. As it does so the phagocyte membrane invaginates to begin to enclose the pathogen
3. As the pathogen is engulfed, the invaginated phagocyte membrane forms a vesicle
(phagosome) around the pathogen
4. Lysosomes move towards the phagosome and fuse with it
5. Hydrolytic enzymes within the lysosomes are released into the phagosome, onto the
pathogen. These enzymes hydrolyse the pathogen.
6. The soluble digested products are absorbed into the cytoplasm of the phagocyte.
All of the above is the non-specific response
Specific Immune Response
Antigens are recognised as foreign. Different pathogens have different antigens causing immune
response to be specific. Lymphocyte having a receptor on its cell surface membrane that is
complementary in shape to the antigen.
Self and non self: In the foetus, lymphocytes make contact with other ‘self’ cells. Lymphocytes that
are complementary in shape with foetal cells are switched off. By the time the baby is born the
functional lymphocytes that remain are those that are not complementary to self-cells.
Types of lymphocyte:
Type Where formed Site of Name of immune Nature of
development response immune
response
B-lymphocyte Stem cells in bone Bone marrow Antibody-mediated Produce antibodies
marrow which responds to
antigens found in
body fluids. Usually
viral or bacterial.
T-lymphocyte Stem cells in bone Thymus gland Cell-mediated Respond to
marrow antigens attached
to body cells.
Usually viral
infection.
