24/04/2023
Immune System & its Cells, an Overview (PY4010)
The immune system causes:
- Inflammation
- Hepatitis
- Aids
- Cold
- Allergy
- Rheumatoid
- MS
- Vaccination reactions
- CVD
- Organ transplant rejection
- Etc.
Immunity:
Immunity is body’s ability to resist/eliminate potentially harmful foreign materials/abnormal
cells
Pathogens:
Infectious agents that cause damage/disease
Pathogens examples
Fungi (eukaryotic), protoctista (eukaryotic), multicellular parasites (eukaryotic), viruses
(prokaryotic), bacteria (prokaryotic). Intracellular - viruses. Extracellular - bacteria.
What is virulence?
Disease-producing power of a pathogen.
What is the immune system?
Protection and repair mechanisms of our body.
Immune system’s key mediators:
Cells (cyte, leuko, macro, phago, poly, morph)
Molecules/soluble factors (antibodies, cytokines, completement, inflammatory, mediators i.e.
histamine)
Exterior defences
Aka non-specific defence mechanisms. Skin and mucous lining blick entry of
viruses/bacteria into the body and provide a hostile environment for microbes. Cells of
mucous membrane produce mucus which traps microbes. Mucous
secretions/saliva/tears/cilia all produce washing actions which “bar” microbes.
Acidity of the stomach destroys microbes in food/water.
Lysozymes digest cell wall(s) of bacteria.
, Tissue fluids contain antimicrobial agents.
Immune cells
Most of the immune system’s cells derive from hepatopoietic stem cells. Each cell type
expresses characteristic surface molecules that identify them i.e. CD markers and receptors.
Granulocytes
Neutrophils, eosinophils, basophils
Contain cytoplasmic granules that specifically stain (acidic, basic, or both) with Wright’s
stain. Granulocytes are usually larger and shorter-lived than other RBCs and have lobed
nuclei and are phagocytic.
Neutrophils
Most numerous leukocytes in blood (60% of WBCs).
Size is 12-15 micrometres in diameter. Nucleus has 2-5 lobes interlinked by fine chromatin
thread. Number of lobes increases with age of cells.
Functions are to phagocytose bacteria, and release antimicrobial agents.
Actively mobile and phagocytic. They patrol tissues as they squeeze out of the capillaries,
constituting a defence against invasion by microorganisms, especially bacteria.
The granules in the neutrophil are lysosomes.
Large numbers of neutrophils are released during infections
Their lifespan is 6-7 hours in the blood, and 2-3 days in the connective tissue. They are
short-lived and die after digesting bacteria. Dead neutrophils make up a large proportion of
pus.
Basophils
Least numerous of leukocytes in blood
Nucleus is U-/S-shaped, or 2-lobed, with 2-3 conspicuous constrictions
Basophilic granules are more irregular in size, stain dark blue (acidic, they are basic) and
stain metachromatically (responding to heat). Granules contain heparin and histamine and
are capable of generating LKs (leukotrienes).
Function of basophils is to secrete histamine (vasodilator) and heparin (anticoagulant).
Basophils can mediate hypersensitivity reactions.
Mast cells
They are long lived tissue-resident cells released into the blood as mast cell progenitors and
don’t fully mature until they’re recruited into the tissue.
They are located at the boundaries between tissues and the external environment i.e.
mucosal surfaces.
They contain granules rich in heparin and histamine that are released when activated by
degranulation.
They have immunoglobulin E (IgE) antibodies bound to their surface and binding of specific
antigens to the IgE will activate them.
They play an important role in many inflammatory settings including host defence to parasitic
infection and in allergic reaction.
Eosinophils
They account for 1-4% of WBCs.
Their diameter is 10-15 micrometres and their nucleus usually has 2 lobes.
The cytoplasm is packed with coarse, bright red-stained granules, which contain various
hydrolytic enzymes including histaminase, arylsulfatase, and peroxidase.
Eosinophils’ functions include to phagocytose antigen-antibody complexes as allergens, and
to release enzymes to weaken or destroy parasites such as worms.
Immune System & its Cells, an Overview (PY4010)
The immune system causes:
- Inflammation
- Hepatitis
- Aids
- Cold
- Allergy
- Rheumatoid
- MS
- Vaccination reactions
- CVD
- Organ transplant rejection
- Etc.
Immunity:
Immunity is body’s ability to resist/eliminate potentially harmful foreign materials/abnormal
cells
Pathogens:
Infectious agents that cause damage/disease
Pathogens examples
Fungi (eukaryotic), protoctista (eukaryotic), multicellular parasites (eukaryotic), viruses
(prokaryotic), bacteria (prokaryotic). Intracellular - viruses. Extracellular - bacteria.
What is virulence?
Disease-producing power of a pathogen.
What is the immune system?
Protection and repair mechanisms of our body.
Immune system’s key mediators:
Cells (cyte, leuko, macro, phago, poly, morph)
Molecules/soluble factors (antibodies, cytokines, completement, inflammatory, mediators i.e.
histamine)
Exterior defences
Aka non-specific defence mechanisms. Skin and mucous lining blick entry of
viruses/bacteria into the body and provide a hostile environment for microbes. Cells of
mucous membrane produce mucus which traps microbes. Mucous
secretions/saliva/tears/cilia all produce washing actions which “bar” microbes.
Acidity of the stomach destroys microbes in food/water.
Lysozymes digest cell wall(s) of bacteria.
, Tissue fluids contain antimicrobial agents.
Immune cells
Most of the immune system’s cells derive from hepatopoietic stem cells. Each cell type
expresses characteristic surface molecules that identify them i.e. CD markers and receptors.
Granulocytes
Neutrophils, eosinophils, basophils
Contain cytoplasmic granules that specifically stain (acidic, basic, or both) with Wright’s
stain. Granulocytes are usually larger and shorter-lived than other RBCs and have lobed
nuclei and are phagocytic.
Neutrophils
Most numerous leukocytes in blood (60% of WBCs).
Size is 12-15 micrometres in diameter. Nucleus has 2-5 lobes interlinked by fine chromatin
thread. Number of lobes increases with age of cells.
Functions are to phagocytose bacteria, and release antimicrobial agents.
Actively mobile and phagocytic. They patrol tissues as they squeeze out of the capillaries,
constituting a defence against invasion by microorganisms, especially bacteria.
The granules in the neutrophil are lysosomes.
Large numbers of neutrophils are released during infections
Their lifespan is 6-7 hours in the blood, and 2-3 days in the connective tissue. They are
short-lived and die after digesting bacteria. Dead neutrophils make up a large proportion of
pus.
Basophils
Least numerous of leukocytes in blood
Nucleus is U-/S-shaped, or 2-lobed, with 2-3 conspicuous constrictions
Basophilic granules are more irregular in size, stain dark blue (acidic, they are basic) and
stain metachromatically (responding to heat). Granules contain heparin and histamine and
are capable of generating LKs (leukotrienes).
Function of basophils is to secrete histamine (vasodilator) and heparin (anticoagulant).
Basophils can mediate hypersensitivity reactions.
Mast cells
They are long lived tissue-resident cells released into the blood as mast cell progenitors and
don’t fully mature until they’re recruited into the tissue.
They are located at the boundaries between tissues and the external environment i.e.
mucosal surfaces.
They contain granules rich in heparin and histamine that are released when activated by
degranulation.
They have immunoglobulin E (IgE) antibodies bound to their surface and binding of specific
antigens to the IgE will activate them.
They play an important role in many inflammatory settings including host defence to parasitic
infection and in allergic reaction.
Eosinophils
They account for 1-4% of WBCs.
Their diameter is 10-15 micrometres and their nucleus usually has 2 lobes.
The cytoplasm is packed with coarse, bright red-stained granules, which contain various
hydrolytic enzymes including histaminase, arylsulfatase, and peroxidase.
Eosinophils’ functions include to phagocytose antigen-antibody complexes as allergens, and
to release enzymes to weaken or destroy parasites such as worms.
