Cells of the Immune system

Question 1

What are the 2 main properties of stem cells?

Answer 1

1) Unspecialised= Able to differentiate into specialised cells, daughter cells which are different to themselves and can function
2) Self renewal= Make more copies of themselves in order to maintain the pool of stem cells for differentiation

Also tend to be immortal= Much more likely to live longer and for longer periods of time

Question 2

What is the difference between totipotency and pluripotent?

Answer 2

Totipotency= Able to differentiate into all cell types 
Pluripotentcy= Able to differentiate into all cell types apart from placenta

Question 3

What are erythrocytes?

Answer 3

They also play a role in defence= Surface complement receptors which bind to complement which are attached to small circulating immune complexes

Important role in clearing immune complexes from circulation in persistent infections

Do not have nucleus or organelles

Question 4

What are lymphocytes?

Answer 4

3 different lymphocytes: Type of leukocytes, provide specificity and memory which are characteristic of the adaptive immune response

1) B-lymphocytes: Responsible for antibody production and antigen presentation
2) T lymphocytes
3) Natural killers

2) and 3) play important roles in defence against intracellular pathogens such as viruses

Question 5

What is innate immune response?

Answer 5

Innate (or natural)= Present at birth, body’s nonspecific immune response to invasion, pattern recognition receptors

No memory or learning, fight off during the early stage to give time for adaptive

Neutrophils are part of this

Membrane receptors= Broad specificity and allow some immune cells to respond to molecular signals that are both unique and common to pathogenic microorganisms

Example: Inflammation

Question 6

What is adaptive immune response?

Answer 6

Adaptive(acquired) immunity:
Specific immune response= Memory and learning of the immune system= Takes longer

Membrane receptors= highly specific and distinguish between different pathogens

Characteristic: Specific immune response following first exposure to pathogen may take days

Repeated exposures= Immune system ‘remembers’ prior exposures and reacts more rapidly

Question 7

What are the different components which adaptive response can split into?

Answer 7

1) Humoural immunity (Antibody-mediated immunity):
-Uses secreted proteins (ANTIBODIES or Immunoglobulin as they are known as…)
-Soluble components of the immune system, anything that can dissolve
-Cytokines: Proteins that stimulate or inhibit cell differentiation and proliferation= Protein messengers released by one cells
-Interleukins: Group of cytokines that enable communication between leukocytes (white blood cells, general name) and particular lymphocytes
-Chemokines: Induces chemotaxis and activation of leukocytes
-Antibodies: Bind to antigens to make them more visible to the immune system
-Complement: Soluble proteins that ‘complement’ the action of antibodies= Can also kill pathogens directly, mainly produced by liver
-Interferons: Have properties of cytokines as they can communication from one cell to another + Interfere in viral infection, have different types:
1) α, β: Anti-viral
γ - interferons: Primary communication and activation of the immune system

Question 8

What are the different components which adaptive response can split into?

Answer 8

2) Cellular mediated immunity
Uses content dependent signalling in which an immune cell binds through receptors to its target cell
-T Cells= Direct action of T cells which distinguishes it from immunity mediated by antibodies

Question 9

What are the different cells of the immune system?

Answer 9

Leukocytes: White blood cells, there are 6 types and are the primary cells responsible for immune system
Basic types: If confused look in textbook page 784
-Granulocytes (general name) given to white blood cells whose cytoplasm contain prominant granules : can then be split into:
1) Basophiles and mast cells: In blood, release chemicals that mediate inflammation and allergic responses
2) Eosinophils: type of cytotoxic cell= Destroy invaders
3) Neutrophils: Ingest and destroy invaders- ALSO phagocytes
-Phagocytes (general name): white blood cells that engulf and ingest their targets by phagocytosis
4) Monocytes and Macrophages: Ingest and destroy, antigen presentation

5) Lymphocytes: Have 3 different types:
B Cells= Plasma cells + Memory cells, Develop in bone marrow, produce antibodies
T cells= Mature in Thymus
Natural Killers= NOT part of adaptive and are lymph cells, part of innate response and kill infected and tumour cells

6) Dendritic cells: Recognise pathogens and activate other immune cells by antigen presentation

ALSO have red blood cells and platelets= NOT considered to be part of immune system= Will not talk about

Question 10

What are the different types of stem cells which haemotopoetic stem cells can split into?

Answer 10

1) Myeloid stem cells= All leukocytes apart from lymphocytes
2) Lymphoid stem cells= Lymphocytes
Specificity of immune response= Lymphocytes, which are small nucleated leukocytes and are found in blood, tissues and lymph
T cells and B cells come from a common precursor= Both produced within the bone marrow

Question 11

What is a potential syndrome which develops if you do not have T cells?

Answer 11

DiGeorge syndrome:

• Thymus does not develop= Essentially no mature T cells produced= Immunoglobulin levels disturbed
• Can lead to candidiasis, pneumonia and diarrhoea

Question 12

What do B cells do?

Answer 12

Produced and mature within the bone marrow
Function: The only cells to produce antibodies (immunoglobulins)
Antibodes: Work against foreign bodies + globular proteins which participate in the humoural immune response

B cells and antibodies: Central to attacking extracellular pathogens such as many bacteria

2 Types:
Plasma cells= Synthesise and secrete antibodies at high rates
Memory cells= B cells which are long lived and stay in the blood

Question 13

What happens when you don’t have B cells?

Answer 13

X-linked infantile hypogammaglobulinanemia:

Inability to produce any immunoglobuin= Likely to be male and young
Show recurrent bacterial infection but can be treated
In the womb: Foetus only takes immunoglobulins (IgGs) that the mother has produced but they do not take B cells= IgGs antibodies are produced in secondary immune response and activate complement

Treatment: Pooling IgG from plasma from blood donors

Question 14

What do T cells do?

Answer 14

Precursors in bone marrow, mature in Thymus
Function: Express a specific antigen receptor

Cannot bind to free floating antigens like B cells

Antibodies: only effective agains extracellular pathogens as they can only bind to SOLUBLE or exposed antigens= once pathogen gets into host cell= Can no longer be ‘seen’ by humour immune system

Important in:

1) Enhancing B cell responses
2) Enhancing phagocyte killing of intracellular bacteria
3) Killing virally infected cells

2 Types:
1) Helper T cells: secrete cytokines which activate other immune cells
2) Cytotoxic T cells: Attack and destroy cells that display MHC-I-antigen complexes
Kill by inducing apoptosis on the target cells

Question 15

What is a potential syndrome which develops if you do not have T cells?

Answer 15

DiGeorge syndrome:

• Thymus does not develop= Essentially no mature T cells produced= Immunoglobulin levels disturbed
• Can lead to candidiasis, pneumonia and diarrhoea

Question 16

What do active B cells and active T cells have?

Answer 16

Active B cells: lots of ER and lots of Golgi

Active T cells: Very fine granules

Question 17

What are the cells which make up innate immunity?

Answer 17

NK cells, macrophages, neutrophils, complement, dendritic cells

Adaptive: T and B cells only

Question 18

What is pattern recognition receptors for innate immunity?

Answer 18

Different types of PRR, one of which are Toll-like receptors:

Toll-like receptors:
They are single, membrane-spanning, non-catalytic receptors usually expressed in antigen presenting cells such as macrophages and dendritic cells, that recognize structurally conserved molecules derived from microbes

Types:

• TLR4= Detects lipopolysaccharide= We do not produce them and they are products of specific types of bacteria which are pathogenic
• TLR3= Detects double stranded RNA= We do not make this either

Do not need to have specific immunity to the as they are non-self

PRR= Play key role in signalling “DANGER” to immune system

Question 19

What are natural killer cells?

Answer 19

• Granular lymphocytes
• Part of innate response against viral infections
• Detect virus infected cells by changes in cell surface molecules, and kill by induce apoptosis before virus can replicate
• BUT complete elimination of the virus requires activation of a specific immune response
• Viruses can interfere with production of MHC= NK cells will kill in absence of MHC expression as they believe it is infected by viruses
• Rare in blood

Question 20

What are dendritic cells?

Answer 20

Antigen-presenting cells 
3 main types: 
1) Langerhans cells (skin) 
2) Interdigitating cells (lymph node) 
3) Follicular (B cell follicle) 

LINK innate to adaptive immunity:

• Present engulfed antigens to B cells and T cells
• Look like neural dendrites
• Process: Dendritic cells recognise and capture antigens –> Migrate to secondary lymphoid tissues —> Present the antigens to lymphocytes

Question 21

What do phagocytes do and what are the different types?

Answer 21

Function:
Phagocytose things= Ingest foreign material such as bacteria, dead and dying cells
Part of innate immunity

Types: Neutrophils, Monocytes and macrophages

Part of myeloid lineage
Macrophages and monocytes could phagocytose and digest pathogen= Antigen-Presenting= T cells can then recognise the antigens

Question 22

What do macrophages do?

Answer 22

Monocytes are the precursor cells of tissue macrophages
Ingest and phagocytose pathogens= Much more efficient than neutrophils + remove larger particles

Antigen-presenting cells

Macrophage can ingest and digest antigens, insert fragments of the processed antigen fragment so that it becomes part of the surface protein complex

Question 23

What are some properties of phagocytes?

Answer 23

1) Sensitive to T cells cytokines= Part of the effector part of the immune response, phagocytose bacteria are killed more efficiently when macrophages are activated by cytokines
2) Uptake of antibody-opsonised particles= Opsonins= Antibodies that tag encapsulated bacteria= convert unrecognisable particles into ‘food’ for phagocytes

Question 24

What are neutrophils?

Answer 24

Function: Recruit inflammatory cells to sites of infection + Ingest and destroy invaders

• Both phagocytes and granulocytes
• Single, multi-lobed nucleus= Have fine blue granules containing proteases and anti-microbial effector molecules
• Produce an oxidative burst following phagocytosis of pathogens= Kill microbes by producing reactive oxygen species

Have properties such as migration, chemotaxis
Need to make half a million neutrophils a second

Phagocytic cells that typically ingest and kill 5-20 bacteria in short programmed life span (one or two days)

Most abundant white blood cell + formed in bone marrow

Most remain in blood but can leave circulation if attracted to an extravascular site of damage or infection
-IF YOU DONT HAVE THEM YOU DIE

Question 25

What are the granulocytes? What are the different types?

Answer 25

Granulocytes= Cytoplasm contains prominent granules, names comes from staining properties of the granules
-All 3: Granule contents are release from the cell by exocytosis= Degranulation

Types:
1) Basophils and mast cells
-Stain dark blue with basic dyes
-Basophils: Circulatory
-Mast Cells: Inhabit the mucosa and connective tissue
Their degranulation is a response to an allergen
-Function: Release chemicals that mediate inflammation and allergic responses
-Involved in acute inflammatory response + important in allergy and hypersensitivity
2) Eosinophils
-Stain with eosin= easy to spot
-Responsible for: Killing parasites that cannot be digested
-Bind to antibody coated parasites —> degranulate –> dissolve the cell surface
-About 1-2% of circulating leukocytes are eosinophils
3) Neutrophils