Introduction to Immune System

Question 1

What are examples of barrier against foreign pathogens?

Answer 1

• Physical
  
  • Mucosal membranes
  • Mucociliary escalator
  • Skin
• Chemical
  
  • Acidic pH of stomach
  • Rapid pH change in duodenum and alkaline pH in jejunum and ileum
  • Skin sebum to lower pH
  • Lyzozymes (anti-bacterial enzyme) in tears, saliva and sweat

Question 2

Describe the anatomy of the immune system?

Answer 2

Formed from

• Lymphoid organs
  
  • Bone marrow
  • Spleen
• Lymph nodes
• Mucosal membranes
  
  • Mucosa-associated lymphoid tissue (LALT)
  • Bronchus-associated lymphoid tissue (BALT)
  • Gut-associated lymphoid tissue (GALT), including Peyer’s patches

Question 3

What are the lymphoid organs?

Answer 3

• Bone marrow
• Spleen

Question 4

What mucosal membranes contribute to the immune system?

Answer 4

• Mucosa-associated lymphoid tissue (LALT)
• Bronchus-associated lymphoid tissue (BALT)
• Gut-associated lymphoid tissue (GALT), including Peyer’s patches

Question 5

What are the cells of the immune system derived from?

Answer 5

Formed in bone marrow from multipotential haematopoietic stem cell (haemocytoblast)

Question 6

What cells form the immune system?

Answer 6

• Megakaryocyte
  
  • Location – bone marrow
  • Structure – lobulated nucleus
  • Function – production of platelets
  • Life span – 7 to 10 days
• Platelets
  
  • Location – bone marrow and circulation
  • Structure – small anucleate disc shaped cell fragments with granules
  • Function – blood clotting
  • Life span – 7 to 10 days
• Erythrocyte
  
  • Location – bone marrow and circulation
  • Structure – biconcave and anucleate
  • Function – transport oxygen, damaged RBC removed via reticuloendothelial system
• Mast cell
  
  • Location – connective tissues and mucous membranes
  • Structure – large granulocyte, granules contain histamine
  • Function – important role in allergy, main cell targets are parasites, activated by cross linking of IgE antibodies bound to their FC receptors, activation resulting in degranulation
  • Life span – few weeks to months
• Basophil
  
  • Location – bone marrow and circulation
  • Structure – granulocyte, granules contain histamine
  • Function – main target parasites, activated by cross-linking of IgE antibodies that they have bound to their FC receptors, activation results in degranulation, also capable of phagocytosis
  • Life span – hours to days
• Neutrophil
  
  • Location – bone marrow and circulation
  • Structure – granulocyte, granules contain substances to kill and digest pathogens such as peroxidase
  • Function – first cells to migrate to site of infection, target is extracellular pathogens like bacteria and fungi, perform phagocytosis or degranulation
  • Life span – few days
• Eosinophil
  
  • Location – bone marrow and circulation, tissues such as lungs and oesophagu
  • Structure – granulocyte, granules contain substances to digest and kill pathogens such as peroxidase
  • Function – targets multicellular parasites too big for phagocytosis, important role in allergy
  • Life span – 8 to 12 days
• Monocyte
  
  • Location – bone marrow and circulation
  • Structure – kidney shaped nucleus
  • Function – migrates to tissue where they become macrophages and dendritic cells in response to inflammation, capable of phagocytosis, large quantities of hydrolytic enzymes
  • Life span – 24 hours
• Macrophage
  
  • Location – bone marrow and are tissue-based progeny of monocytes, name changes depending on what tissue in
  • Function – phagocytosis, antigen presenting cell to CD4⁺ Th cells, cytokine release (TNF-alpha, IL-2, IL-6)
  • Life span – months to years
• Dendritic cell
  
  • Location – tissues exposed to external environment
  • Structure – long narrow processes which resemble neuronal dendrites
  • Function – antigen presenting cell to CD4⁺ T cells via MHC II, phagocytosis, cytokine secretion (TNF-alpha, IL-12, IL-23)
  • Life span – days to weeks
• Natural killer cell
  
  • Location – bone marrow, circulation and spleen
  • Structure – large granular lymphocyte, granules contain special proteins such as perforin and proteases
  • Function – activated by IFN and macrophage derived cytokines, or activated by abnormal MHC I signals (cancerous cells or virally infection cells) to cause apoptosis of cell
• T-lymphocyte
  
  • Location – completes maturation in thymus, mature T cells reside in bone marrow, circulation and places such as lymph nodes
  • Structure – all T cells express T cell receptors on their cell surface, there are 3 types: Helper T cells (CD4⁺), Cytotoxic T cells (CD8⁺) and Regulatory T cells (CD4⁺, CD25⁺)
  • Function – involved in cell mediated adaptive immune response
• B-lymphocyte
  
  • Location – completes maturation within lymph nodes and spleen, mature B cells reside in bone marrow, circulation and lymph nodes
  • Structure – all B cells express B cell receptors on surface, 2 kinds: plasma B cells and memory B cells
  • Function – involved in humoral mediated adaptive immune response by producing specific antibodies against certain antigens

Question 7

For megakaryocyte:

• location
• structure
• function
• life span

Answer 7

• Megakaryocyte
  
  • Location – bone marrow
  • Structure – lobulated nucleus
  • Function – production of platelets
  • Life span – 7 to 10 days

Question 8

For platelets:

• location
• structure
• function
• life span

Answer 8

• Location – bone marrow and circulation
• Structure – small anucleate disc shaped cell fragments with granules
• Function – blood clotting
• Life span – 7 to 10 days

Question 9

For erythrocyte:

• location
• structure
• function

Answer 9

• Location – bone marrow and circulation
• Structure – biconcave and anucleate
• Function – transport oxygen, damaged RBC removed via reticuloendothelial system

Question 10

For mast cell:

• location
• structure
• function
• life span

Answer 10

• Mast cell
  
  • Location – connective tissues and mucous membranes
  • Structure – large granulocyte, granules contain histamine
  • Function – important role in allergy, main cell targets are parasites, activated by cross linking of IgE antibodies bound to their FC receptors, activation resulting in degranulation
  • Life span – few weeks to months

Question 11

For basophil:

• location
• structure
• function
• life span

Answer 11

• Basophil
  
  • Location – bone marrow and circulation
  • Structure – granulocyte, granules contain histamine
  • Function – main target parasites, activated by cross-linking of IgE antibodies that they have bound to their FC receptors, activation results in degranulation, also capable of phagocytosis
  • Life span – hours to days

Question 12

For neutrophil:

• location
• structure
• function
• lifespan

Answer 12

• Neutrophil
  
  • Location – bone marrow and circulation
  • Structure – granulocyte, granules contain substances to kill and digest pathogens such as peroxidase
  • Function – first cells to migrate to site of infection, target is extracellular pathogens like bacteria and fungi, perform phagocytosis or degranulation
  • Life span – few days

Question 13

For eosinophil:

• location
• structure
• function
• life span

Answer 13

• Eosinophil
  
  • Location – bone marrow and circulation, tissues such as lungs and oesophagu
  • Structure – granulocyte, granules contain substances to digest and kill pathogens such as peroxidase
  • Function – targets multicellular parasites too big for phagocytosis, important role in allergy
  • Life span – 8 to 12 days

Question 14

For monocyte:

• location
• structure
• function
• life span

Answer 14

• Location – bone marrow and circulation
• Structure – kidney shaped nucleus
• Function – migrates to tissue where they become macrophages and dendritic cells in response to inflammation, capable of phagocytosis, large quantities of hydrolytic enzymes
• Life span – 24 hours

Question 16

For macrophage:

• location
• function
• life span

Answer 16

• Location – bone marrow and are tissue-based progeny of monocytes, name changes depending on what tissue in
• Function – phagocytosis, antigen presenting cell to CD4⁺ Th cells, cytokine release (TNF-alpha, IL-2, IL-6)
• Life span – months to years

Question 17

What cytokines do macrophages release?

Answer 17

(TNF-alpha, IL-2, IL-6)

Question 18

For dendritic cell:

• location
• structure
• function
• lifespan

Answer 18

• Dendritic cell
  
  • Location – tissues exposed to external environment
  • Structure – long narrow processes which resemble neuronal dendrites
  • Function – antigen presenting cell to CD4⁺ T cells via MHC II, phagocytosis, cytokine secretion (TNF-alpha, IL-12, IL-23)
  • Life span – days to weeks

Question 19

What cytokines do dendritic cells release?

Answer 19

(TNF-alpha, IL-12, IL-23)

Question 20

For NK cell:

• location
• structure
• function

Question 21

For T cell:

• location
• structure
• function

Question 22

For B cell:

• location
• structure
• function

Answer 22

• Location – completes maturation within lymph nodes and spleen, mature B cells reside in bone marrow, circulation and lymph nodes
• Structure – all B cells express B cell receptors on surface, 2 kinds: plasma B cells and memory B cells
• Function – involved in humoral mediated adaptive immune response by producing specific antibodies against certain antigens

Question 23

What are the 2 divisions of the immune system?

Answer 23

• Innate immunity
• Adaptive immunity
  
  • Cell mediated – T cell
  • Humoral mediated – B cell

Question 24

What do the innate and adaptive immune system differ in?

Answer 24

They differ from each other in speed of response time, cellular components and functions:

• Innate is fast to response but not specific, adaptive is slower to respond but is specific to pathogen and creates immunological memory, allowing for faster response next time same pathogen

Question 25

What does MHC stand for?

Answer 25

Major histocompatibility complex

Question 26

What are the 2 types of MHC?

Answer 26

* Class 1 * Found on cell surface of all nucleated cells in body * Display self-markers but also responsible for presenting intracellular forign antigens to immune system * Class 2 * Found only on professional antigen presenting cells, such as dendritic cells, macrophages and B lymphocytes * Responsible for presenting extracellular antigens from pathogens * Brings antigen to attention of T cells

Question 27

What is MHC also referred to as?

Answer 27

* Also referred to as human leukocyte antigen (HLA)

Question 28

What does HLA stand for?

Answer 28

Human leukocyte antigen

Question 29

What cells do MHC I and MHC II molecules present antigens to?

Answer 29

MHC I receptor presents antigens to CD8⁺ cytotoxic T cells, which destroy them MHC II receptor on antigen presenting cells presents their antigen to CD4⁺ helper T cells, causing it to release cytokines that activates B cells, which release specific antibodies against the pathogen to improve macrophage phagocytosis and recruit primed CD8⁺ cells to target pathogen Sometimes immune cells can attack our own cells that are displaying self-antigens, this is autoimmunity

Question 30

What is immune tolerance?

Answer 30

This is when our immune cells do not attack our own cells, achieved through: * Central tolerance * Peripheral tolerance

Question 31

What are the 2 forms of immune tolerance?

Answer 31

* Central tolerance * Peripheral tolerance

Question 32

Where does central tolerance occur?

Answer 32

* T cells in thymus * B cells in bone marrow

Question 33

What happens in central tolerance?

Answer 33

* Any cell showing inappropriate response to self-antigens are either edited, transformed or destroyed

Question 34

Where does periphral tolerance occur?

Answer 34

* Occurs in secondary lymphoid organs * Contains mature cells already released into circulation

Question 35

What happens in peripheral tolerance?

Answer 35

* If any cell inappropriately recognises and reacts to self-antigens they are made useless, destroyed or suppressed by regulatory T cells

Question 36

What can immune tolerance be exploited by?

Answer 36

Immune tolerance can be exploited by intracellular pathogens or malignant cells to evade host immune responses