Cell recognition and the immune system
Physical barriers to infection include:
Skin which is a tough physical barrier consisting of keratin.
Stomach acid (hydrochloric acid) which kills bacteria.
Gut and skin flora – natural bacterial flora competes with pathogens for
food and space.
The immune system responds to antigens which are found on the surface of
cells. These are proteins that have a complex structure that is unique for each
cell and therefore identifies the cell as self or non-self.
Non Specific Immune Response
Non-specific responses of the body to infection include:
Inflammation – histamines released by damaged white tissues cause
vasodilation which increases the flow of blood to the infected area and
increases permeability of blood vessels. As a result of that antibodies,
white blood cells and plasma leak out into the infected tissue and
destroy the pathogen.
Lysozyme action – lysozyme are enzymes found in secretions such as
tears and mucus which kill bacterial cells by damaging their cell wall.
Interferon – interferons prevent viruses spreading to uninfected cells by
stopping protein synthesis in viruses.
Phagocytosis-
- Chemical products of pathogens attract the phagocyte and cause it to
move towards it
- Phagocytes have several receptors on their cell surface membrane
that recognise and attach to chemicals on the pathogen
- They engulf the pathogen to form a vesicle called a phagosome
- Lysosomes move towards the vesicle and fuse with it
- Lysosomes release lysozymes which destroy the ingested bacteria by
hydrolysing its cell wall
- The soluble/ useful products from the breakdown of the pathogen
are ingested by the phagocyte
- After the pathogen is engulfed and destroyed, its chemical markers
called antigens are then presented on the surface of the phagocyte.
The phagocyte then becomes an antigen presenting cell which
activates a specific immune response if the antigen is recognised as
foreign.
Phagocytes- ingest and destroy the pathogen by phagocytosis before it can
cause harm
, Lymphocytes- involved in immune responses
Specific immune response
The specific immune response is antigen specific and produces responses
specific to one type of pathogen only. It is slower at first, but it provides long-
term immunity. This type of immune response relies on lymphocytes:
- B cells mature in the bone marrow and are involved in the humoral
response.
- T cells move from the bone marrow to the thymus gland where they
mature and are involved in cell mediated response.
Specific immune response glossary:
- Memory cells are cells which replicate themselves when exposed to
an invading pathogen and remain in the lymph nodes for decades.
This results in a much faster immune response should the individual
be infected by the same pathogen again.
- B effector or plasma cells are antibody producing cells.
- T helper cells stimulate B cells and T killer cells to divide.
- T killer cells destroy pathogen infected cells.
Physical barriers to infection include:
Skin which is a tough physical barrier consisting of keratin.
Stomach acid (hydrochloric acid) which kills bacteria.
Gut and skin flora – natural bacterial flora competes with pathogens for
food and space.
The immune system responds to antigens which are found on the surface of
cells. These are proteins that have a complex structure that is unique for each
cell and therefore identifies the cell as self or non-self.
Non Specific Immune Response
Non-specific responses of the body to infection include:
Inflammation – histamines released by damaged white tissues cause
vasodilation which increases the flow of blood to the infected area and
increases permeability of blood vessels. As a result of that antibodies,
white blood cells and plasma leak out into the infected tissue and
destroy the pathogen.
Lysozyme action – lysozyme are enzymes found in secretions such as
tears and mucus which kill bacterial cells by damaging their cell wall.
Interferon – interferons prevent viruses spreading to uninfected cells by
stopping protein synthesis in viruses.
Phagocytosis-
- Chemical products of pathogens attract the phagocyte and cause it to
move towards it
- Phagocytes have several receptors on their cell surface membrane
that recognise and attach to chemicals on the pathogen
- They engulf the pathogen to form a vesicle called a phagosome
- Lysosomes move towards the vesicle and fuse with it
- Lysosomes release lysozymes which destroy the ingested bacteria by
hydrolysing its cell wall
- The soluble/ useful products from the breakdown of the pathogen
are ingested by the phagocyte
- After the pathogen is engulfed and destroyed, its chemical markers
called antigens are then presented on the surface of the phagocyte.
The phagocyte then becomes an antigen presenting cell which
activates a specific immune response if the antigen is recognised as
foreign.
Phagocytes- ingest and destroy the pathogen by phagocytosis before it can
cause harm
, Lymphocytes- involved in immune responses
Specific immune response
The specific immune response is antigen specific and produces responses
specific to one type of pathogen only. It is slower at first, but it provides long-
term immunity. This type of immune response relies on lymphocytes:
- B cells mature in the bone marrow and are involved in the humoral
response.
- T cells move from the bone marrow to the thymus gland where they
mature and are involved in cell mediated response.
Specific immune response glossary:
- Memory cells are cells which replicate themselves when exposed to
an invading pathogen and remain in the lymph nodes for decades.
This results in a much faster immune response should the individual
be infected by the same pathogen again.
- B effector or plasma cells are antibody producing cells.
- T helper cells stimulate B cells and T killer cells to divide.
- T killer cells destroy pathogen infected cells.
