CBI20306: Cell Biology and Health
Immunology
Chapter 1: Introduction to the immune system
The immune system is a network of cells, tissues and organs that work together to defend the body against
attacks by microbes (tiny infections causing-organisms, such as bacteria, viruses, parasites and fungi). The
immune system is quite complex and can recognize and remember millions of different pathogens. Immune
cells produce cytokines to allow the immune cells to regulate their own growth and behaviour, enlist their
fellow, and direct new recruit to trouble spots.
There are three lines of defence are physical barriers (skin, digestive system, respiratory and reproductive
tracts), the innate (non-specific) immune system and the adaptive (specific) immune system.
The distinction between ‘self’ and ‘non-self’ is made via peptide presentation in the major histocompatibility
complex (MHC). Anything that trigger the immune response is called an antigen. Tissues or cells from
another person also carry non-self markers and acts as antigens. With an autoimmune disease, the body
launches an attack on ‘self’ cells. With an allergy, the immune system reacts to a seemingly harmless foreign
substance.
All immune cells originate from stem cells in the bone marrow. The cells are derived from the myeloid and
lymphoid lineage.
Monocytes are large cells with an irregular shape and a kidney shaped nucleus. After they leave the
bloodstream, they differentiate into macrophages. When they encounter a pathogen, they will phagocytose
the pathogen into a phagosome. The phagosome will fuse with lysosome.
Lymphocytes are cells of the adaptive immune system and are small round cells that are almost completely
filled by the nucleus. When this cell becomes activated, the cytoplasm will increase.
Natural Killer (NK) cells are cells from the lymphoid lineage. It is a short-lived cell. Most of them are found in
the blood, spleen or liver.
Neutrophils are cells of the innate immune system. They have a three-lobed nucleus and many small
granules in the cytoplasm. The cells are ‘on call’ and can kill rapidly. They are short-lived and die through
programmed cell death (apoptosis). A person cannot survive without neutrophils. Neutrophils can commit
suicide, leave a web of sticky threads, and trap bacteria.
Eosinophils are cells of the innate immune system. They have a two-lobed nucleus and granules in the
cytoplasm. These cells are involved in the protection against parasites. They will degranulate in the presence
of large pathogens. The content of the granules will destruct the skin of the parasite and in such a manner
kill them.
Basophils are cells of the innate immune system. They have a two-lobed nucleus and large dense granules in
the cytoplasm. It also takes part in the protection against parasites by degranulation.
Mast cells are cells of the innate immune system. They have a central oval shaped nucleus and are very long-
lived cells. Their primary function is in the defence against parasites, but they also play a part in the defence
against bacteria by phagocytosing opsonized bacteria. Histamine is stored in their granules and takes part in
allergic reactions.
The proteins that are specific for the type of cell are called ‘cluster of differentiation’ (CD) molecules. When
the cell has a CD molecule, it is called CD+.
Cells of the immune system communicate with one another by exchanging cytokines. They include
interleukins, interferons and growth factors. Some cytokines are chemical switches that turn certain immune
cell types on (activate) and off (inhibit).
Chemokines are released by cells at a site of injury or infection and call other immune cells. They often play a
key role in inflammation.
Pro-inflammatory cytokines act to make disease worse and anti-inflammatory cytokines serve to reduce
inflammation and promote healing.
In low concentration, cytokines act on nearby cells and may even enhance the activity of the cell it is
produced by causing positive feedback. In higher concentrations, cytokines may have a systemic effect
activating cells in several organs. When an immune response is too great or uncontrolled, high
concentrations of cytokines are produced and can lead to a cytokine storm or septic shock.
Immunology
Chapter 1: Introduction to the immune system
The immune system is a network of cells, tissues and organs that work together to defend the body against
attacks by microbes (tiny infections causing-organisms, such as bacteria, viruses, parasites and fungi). The
immune system is quite complex and can recognize and remember millions of different pathogens. Immune
cells produce cytokines to allow the immune cells to regulate their own growth and behaviour, enlist their
fellow, and direct new recruit to trouble spots.
There are three lines of defence are physical barriers (skin, digestive system, respiratory and reproductive
tracts), the innate (non-specific) immune system and the adaptive (specific) immune system.
The distinction between ‘self’ and ‘non-self’ is made via peptide presentation in the major histocompatibility
complex (MHC). Anything that trigger the immune response is called an antigen. Tissues or cells from
another person also carry non-self markers and acts as antigens. With an autoimmune disease, the body
launches an attack on ‘self’ cells. With an allergy, the immune system reacts to a seemingly harmless foreign
substance.
All immune cells originate from stem cells in the bone marrow. The cells are derived from the myeloid and
lymphoid lineage.
Monocytes are large cells with an irregular shape and a kidney shaped nucleus. After they leave the
bloodstream, they differentiate into macrophages. When they encounter a pathogen, they will phagocytose
the pathogen into a phagosome. The phagosome will fuse with lysosome.
Lymphocytes are cells of the adaptive immune system and are small round cells that are almost completely
filled by the nucleus. When this cell becomes activated, the cytoplasm will increase.
Natural Killer (NK) cells are cells from the lymphoid lineage. It is a short-lived cell. Most of them are found in
the blood, spleen or liver.
Neutrophils are cells of the innate immune system. They have a three-lobed nucleus and many small
granules in the cytoplasm. The cells are ‘on call’ and can kill rapidly. They are short-lived and die through
programmed cell death (apoptosis). A person cannot survive without neutrophils. Neutrophils can commit
suicide, leave a web of sticky threads, and trap bacteria.
Eosinophils are cells of the innate immune system. They have a two-lobed nucleus and granules in the
cytoplasm. These cells are involved in the protection against parasites. They will degranulate in the presence
of large pathogens. The content of the granules will destruct the skin of the parasite and in such a manner
kill them.
Basophils are cells of the innate immune system. They have a two-lobed nucleus and large dense granules in
the cytoplasm. It also takes part in the protection against parasites by degranulation.
Mast cells are cells of the innate immune system. They have a central oval shaped nucleus and are very long-
lived cells. Their primary function is in the defence against parasites, but they also play a part in the defence
against bacteria by phagocytosing opsonized bacteria. Histamine is stored in their granules and takes part in
allergic reactions.
The proteins that are specific for the type of cell are called ‘cluster of differentiation’ (CD) molecules. When
the cell has a CD molecule, it is called CD+.
Cells of the immune system communicate with one another by exchanging cytokines. They include
interleukins, interferons and growth factors. Some cytokines are chemical switches that turn certain immune
cell types on (activate) and off (inhibit).
Chemokines are released by cells at a site of injury or infection and call other immune cells. They often play a
key role in inflammation.
Pro-inflammatory cytokines act to make disease worse and anti-inflammatory cytokines serve to reduce
inflammation and promote healing.
In low concentration, cytokines act on nearby cells and may even enhance the activity of the cell it is
produced by causing positive feedback. In higher concentrations, cytokines may have a systemic effect
activating cells in several organs. When an immune response is too great or uncontrolled, high
concentrations of cytokines are produced and can lead to a cytokine storm or septic shock.
