44.1 Blood cells Flashcards
1
Q
Why do red blood cells stain pink in H&E staining?
A
Haemoglobin is a basic protein, so binds to acidic dyes - the pink colour isn’t to do with the haemoglobin itself but rather the eosin staining
2
Q
What is the average size of a red blood cell?
A
7 microns (more specifically 7.5um)
3
Q
What does a red blood cell lack?
A
Red blood cells have no nucleus, no DNA and no organelles
4
Q
How can white blood cells be distinguished from all the red blood cells?
A
WBCs contain nucleic acids which show up purple under H&E staining - RBCs do not so just stain pink
5
Q
How is the shape of a RBC maintained?
A
- Specific shape affected by water content (osmotic effects of solutes)
- Maintained mostly by cytoskeleton
- > spectrin
- > ankyrin
- > other membrane proteins
6
Q
What are discocytes?
A
A normal mature red blood cell with a biconcave disc structure
7
Q
What are stomatocytes?
A
Red blood cells that are slightly more ‘blown up’ than normal discocytes, have a central ‘slit-like’ appearance under a microscope (rather than central paler circle, the shape is a slit)
Often seen in alcoholic liver disease
8
Q
What are echinocytes?
A
Also known as burr cells, a type of red blood cell that has an unusual cell membrane causing many evenly-spaced spiky projections to be present
Sometimes appear as an artefact of staining and putting on to a slide, but can also be an indicator of disease
9
Q
Why is it beneficial that erythrocytes can deform?
A
Because it allows them to pass through arterioles and capillaries - RBC diameter is around 7um, whereas capillary diameter can be about 5um
They tend to stay in the centre of vessels (this is helped by their biconcave shape) - circumference of vessel is often plasma-dense
10
Q
Why is it difficult to make artificial substitutes for blood?
A
Because of its natural visco-elastic properties
11
Q
How does viscosity of blood change with velocity and why?
A
As velocity INCREASES, viscosity DECREASES
- Blood flow in small vessels is low (1mm/s) causing a high viscosity
- This is due to the formation of rouleaux (the adherence of RBCs to each other and vessel walls, allowed through discoid shape)
- RBCs appear more rigid as shear forces (planar forces that occur in fluids due to bodies moving past each other) no longer enough to cause deformation
12
Q
When is the rouleaux effect even more noticeable?
A
- If membrane is more rigid (e.g. in spectrin defects)
- When erythrocytes are older/more aged (aggregate formation increases with age and decreased sialic acid conc in RBC reduces the negative charge, making the formation of a rouleaux more likely)
- If there are inclusions inside cells (e.g. sickle cells in sickle cell anaemia)
13
Q
- Why does sickle cell anaemia cause painful episodes?
A
- This is because the shape of the RBCs make them more likely to form a rouleaux (shape is caused by mutation in a gene that helps to form haemoglobin, recessive)
- These cause blockages in small vessels (capillaries most often)
- The blockages lead to vascular occlusions, restricting flow of oxygen and nutrients to certain areas that will them cause painful crises
14
Q
What are the benefits of a RBC being anucleate?
A
- Better SA:Vol ratio, allows about 25% more surface area than is spherical which improves gas exchange
- Improves deformability to fit through capillaries which often have diameters smaller than that of the RBC
- Less work for the heart as a pump, as the heart pumps approx. 3kg of erythrocytes per min, 40% of that mass would be nucleus
- > saves about 1 to 1.5 tons per day
15
Q
What are the disadvantages of a RBC being anucleate?
A
- No further protein synthesis or repair, so cells will wear out with a lifespan of approx. 120 days
-> this means that an efficient new cell replacement system is needed and a constant turnover of new RBCs (erythropoiesis) - Cell can’t adapt to different conditions, they are terminally differentiated and highly specialised, e.g. cannot respond to high altitudes/low pO2
( - The same goes for blood platelets/thrombocytes)
16
Q
What are the words for RBC and platelet production?
A
RBC: erythropoiesis
Platelet/thrombocyte: thrombopoiesis
17
Q
What is the normal turnover time for a RBC?
A
120 days
IMPORTANT, IS ON SPEC
18
Q
How do RBCs synthesis ATP?
A
No mitochondria, so only use anaerobic respiration
-> rely heavily upon blood glucose
19
Q
Why do RBCs need ATP?
A
- No large energy requirement
- ATP only really needed for membrane-asscoates ATP-dependant Na+/K+ ion exchanger
- > maintains concentrations of ions both in plasma and the RBC
20
Q
What are the plasma and RBC concentrations of sodium and potassium ions?
A
Plasma: - Na+ 140mM - K+ 3.5-5mM RBC: - Na+ 6mM - K+ approx. 100-140mM
21
Q
- What concentration of extracellular potassium ions causes hyperkalaemia and how can this occur?
A
Conc: 7 mM
Caused by RBC lysis (which is in turn caused by high osmotic pressure/hypotonic solutions), which releases a high amount of potassium ions due to the high intracellular concentration
22
Q
What are the three components of a RBC?
A
- Haemoglobin
- Enzymes for metabolising glucose
- Ions (mostly potassium, maintains ion gradient for other processes)
23
Q
- What are some properties of haemoglobin in RBCs?
A
- Globular protein
- 2 alpha subunits, 2 beta subunits
- Around 650 million molecules per cell
- Haem prosthetic group, one Fe2+ per haem group
- > this is about 2/3s of the body’s iron
- > RBCs maintain reducing conditions (therefore no oxidative phosphorylation/mitochondria, achieved through the presence of glucose) to prevent iron from oxidising to Fe3+ which would form methaemoglobin
- Haemoglobin allows the transport of O2 and CO2 (see later flashcards)
24
Q
What glycolytic intermediate has a particular effect within RBCs and what is it?
A
- 2,3-biphosphoglycerate (2,3-BPG, used to be called 2,3-DPG)
- Produced by an erythrocyte enzyme
- Shifts dissociation curve to unload O2 from HbO2 (oxyhaemoglobin)
- > this is due to the fact that if ion pump activity increases it indicates that nearby tissues are respiring, more ATP is needed to maintain action of pumps so more of 2,3-BPG is produced as respiratory/glycolytic intermediate (and this is main energy source for RBC), encourages RBC to unload oxygen at respiring tissue
25
What is and what is the importance of the pentose phosphate pathway/shunt?
- Alternate pathway to glycolysis that involves NADPH
- Pathway uses G6PDH (glucose-6-phosphate dehydrogenase, X-linked enzyme)
- > deficiency (caused by eating too many broad beans (Favism, linked to the Mediterranean region) or by the now-obsolete anti-malaria drug Pamaquine, both are examples of oxidative stressors) results in serious haemolytic crises/anaemia
- Generation of NADPH slows accumulation of oxidised proteins that are associated with erythrocyte aging
- > maintains glutathione, a cysteine-containing tripeptide, in a reduced state
- Allows RBCs to remain in reduced conditions and therefore live longer
26
* What is crenation?
This is where cells shrink because they are in hypertonic solutions (e.g. water potential of cell > water potential of surrounding solution), so water travels out of the cell, causing them to shrink in size/the membranes to become noticeably crumbled under a microscope
27
What are the different types of solutions?
- Hypertonic (water potential lower than that of the cell, >300 mOsmoles)
- Isotonic (water potential same as that of the cell, around 300 mOsmoles)
- Hypotonic (water potential higher than that of the cell, around <300 mOsmoles)
28
What are RBCs ghosts and what do they indicate?
Red blood cells without any contents (e.g. only the membrane remains)
- Indicator of disease (e.g. haemolytic anaemia) or hypotonic solutions
- Can be created in vitro, useful for discovering the presence of the phospholipid bilayer
29
What is osmolarity?
Another word for the osmotic concentration, i.e. the concentration of a solution expressed as the total number of solute particles per litre (osmotically active particles need to be counted, include ions in this)
30
What are the features of an RBC membrane?
- Semi-permeable
- Allows water to permeate through the presence of aquaporins (does mean that cells will lyse if not in a isotonic solution)
- Band 3 complex, allows attachment to glycoproteins extracellularly (these are involved in blood group determination) and the cytoskeleton of ankyrin and various spectrins internally
31
How do RBCs 'age'?
Through the accumulation of oxidised proteins/oxidation products, lifespan prolonged by pentose phosphate shunt but still limited to a turnover rate of around 120 days
32
How can erythrocyte lifespan be shortened?
- Through an abnormal shape
- > haemoglobin mutation, results in thalassaemia and sickle cell anaemia amongst others
- > cytoskeletal proteins are altered through mutations, results in hereditary spherocytosis
- Through RBC clearance mechanisms being accelerated
- > old RBCs are broken down in the spleen and the liver
- > this can be caused by autoimmune diseases (causing the RBCs to be covered in antibodies, triggering phagocytosis by macrophages) or if the macrophages are too active due to a disorder
33
Where are RBCs broken down?
By macrophages in the liver and the spleen
- In the liver, the specific hepatocytes/stellate (star-shaped) macrophages are known as Kupffer cells, and line the sinusoids
34
What effect does the sickle shape of RBCs in sickle cell anaemia have?
- Causes a drastic rearrangement of membrane proteins which signals to macrophages that they should be broken down
- > broken down at a faster rate than possible for the liver to deal with, resulting in a build up of bilirubin and jaundice
- Shape of cells makes them more likely to aggregate/form rouleaux, these block capillaries and cause vascular occlusions/painful crises
35
What are the causes and effects of hereditary spherocytosis?
This is where RBCs are spherical rather than biconcave
- Band III, spectrin and ankyrin defects
- > results in a deficiency and failure to join cytoskeleton to cell membrane, causing abnormal shape
- Loss of membrane surface area in biconcave disc (micro-spherocytosis)
- This causes decrease in RBC deformability and osmotic fragility/more susceptible to osmotic changes
- Accumulate/become trapped in the splenic cords, regions between sinusoids in the spleen
- Conditioning in the spleen causes a further decrease in SA
- More likely to be broken down by macrophages due to severe abnormalities, causes anaemia/deficiency in RBCs
Can cause splenomegaly (big ol' spleen) which can be surgically reduced to remove pain within it, but removes a way through which the sickle RBCs are removed/regulated
36
How does the Till and McCullough experiment work?
- Obtain cells from the bone marrow, blood and spleen (contains progenitor cells) and place in a cell suspension
- Irradiate a mouse with a fatal dose
- Once irradiated, control mice would die (as progenitor cells killed off) but mice injected with the cell suspension live
- > mice were then killed and dissected, new colonies were observed to be growing on the spleen
- > transferral was proven by the fact that new colonies would contain XY chromosomes even in female mice if originally derived from a male
37
What is the difference between stem and progenitor cells?
Progenitor cells are more specific/more differentiated or committed (they are committed to a particular pathway) cells than stem cells, but still have the ability to divide into a few different cell types
More limited self-renewal properties than stem cells, but still some of that characteristic present
38
* What is age-related (pernicious) anaemia?
This is where stem and progenitor cells wear out over time, resulting in a decreased output of RBCs/decreased erythropoiesis which will present as anaemia
39
* What are some stats about erythropoiesis?
- Around 2 x10^11 new RBCs per day per 70kg man (around 1 x10^10 per hour)
- Total new blood cell production including platelets and neutrophils comprises entire body weight in cells every 7 years
- Bone marrow weighs about 3kg in an adult human, distributed throughout the long bones
40
What are the sources of haemopoietic stem cells?
- Bone marrow in adults (red = RBCs, platelets, most WBCs, yellow = some WBCs, colour depends on fat content)
- Liver in foetus
- Embryonic yolk sac
- Early embryonic aorto-gonad-mesonephros region (mesoderm, from para-aortic splanchnopleuric region which is located at the caudal end)
- Umbilical cord blood at childbirth (fancy name: parturition)
41
How can cells be tested for stem cell properties?
Using Till-McCullough experiment variants
- Remove all bone marrow using radiation or chemo- treatment
- Transplant cells being tested
- Determine whether some or all blood cell types have been replaced after recovery and blood cell repopulation (if all, then indicates that some pluripotent stem cells are present in transplanted cells)
- In theory, the bone marrow of the host could now be transplanted further into other mice/is back to normal if the stem cells are present
42
What is the fate of the RBC progenitor nucleus once it has been ejected?
Once ejected from normoblasts, nucleus is digested by macrophages
43
What hormone is used to control erythropoiesis and how does it work?
Erythropoietin (EPO)
- Stimulus is detected in the kidney (or to lesser extent the liver)
-> this could be hypoxia due to a decreased RBC count, less O2 available e.g. due to altitude changes or increased demands from tissue for O2 over a long period of time (full response for this hormone is relatively slow)
- Low O2 blood content causes kidney to release EPO into the blood stream
- EPO stimulates red bone marrow to produce more RBCs/for the progenitors there to divide and differentiate
-> this can cause issues in long-distance athletes treated with EPO as the increased blood count can result in the formation of random clots which can be fatal
- The higher RBC count increases the ability of the blood to carry oxygen, therefore resolving the initial imbalance/hypoxia detected (negative feedback)
- EPO is also mediated by the current amount of haemoglobin present in the blood, e.g. has a higher response to lower masses per unit volume of haemoglobin within RBCs
(Sir Peter J Radcliffe won Nobel prize in 2019 for how cells respond to oxygen)
44
What do the terms normoxia and hypoxia mean?
Normoxia: normal levels of oxygen/at a stable state
Hypoxia: low levels of oxygen or a deprivation, can be local, in a region or of the whole body
(There is also hyperoxia, where the oxygen levels are so high that they become toxic, e.g. inhaling pure oxygen at high atmospheric pressures)
45
What is haemoglobin broken down into and where?
- Haem -> Biliverdin -> Bilirubin
- This occurs in macrophages in the liver and spleen, bilirubin is then transferred to the kidneys or small intestine via bile (excreted as urine and faeces respectively)
- If this molecule builds up it appears yellow and causes the disease jaundice
- The Fe2+ ion is conserved and transported to red bone marrow through the use of a molecule called transferrin in the circulation to be recycled
46
What is a haemocrit?
A measure of what percentage of a blood sample is made up of red blood cells (as opposed to WBCs and platelets which are also in the plasma)
47
What is a buffy coat?
Part of the haemocrit, is the layer above the packed RBCs and contains a mixture of platelets and WBCs - above the buffy coat lies the plasma
48
What are the numbers for different cells per litre of blood and the breakdown for WBCs??
```
RBCs (erythrocytes): 5 x10^12 cells per litre
WBCs (leukocytes): around 7 x10^9 cells per litre
Differential count for WBCs:
40-70% neutrophils
20-40% lymphocytes
Around 6% monocytes
Around 3% eosinophils
<1% basophils
```
49
What are the normal ranges for RBCs in male and female haemocrits (Hcts)?
Male: 40.7-50.3%
Female: 36.1-44.3%
50
What is the difference between normocytic, microcytic and macrocytic anaemia?
- Microcytic is where the RBCs are smaller than usual and are often hypochromic (low in haemoglobin), most commonly caused by an iron deficiency
- Normocytic is where the RBCs are a normal shape and constituency (although some can also be hypochromic), there are just fewer of them in circulation which results in anaemic symptoms (except thalassemia which has a high RBC count)
- Macrocytic is where the RBCs are larger than normal but like other types of anaemia, the haemoglobin content of the cells is low
51
What are the different types of microcytic anaemia?
High RBC count:
- Thalassemia (mutation in haemoglobin protein, causes abnormal RBCs and rapid RBC destruction as well as a reduced capacity to carry O2), both alpha and beta strands, may be combined with other haemoglobin disorders
Low or normal RBC count:
- Iron-deficiency anaemia (reduced ability to produce haemoglobin)
- Lead poisoning (impairs haem synthesis pathway)
- Anaemia of chronic inflammation (inflammation prevents use of stored iron)
- Sideroblastic anaemia (can be caused by excessive alcohol consumption, iron is present but the pathway to create haemoglobin is inhibited, causing iron to accumulate in mitochondria of immature RBCs)
52
What are the different types of normocytic anaemia?
- Haemolytic anaemias (RBCs destroyed faster than they can be made, no main cause known, related to different stresses, anaemias such as thalassemia or sickle cell anaemia or late stage kidney or liver failure)
- Bone marrow disorders (e.g. aplastic anaemia, bone marrow contains RBC stem cells and progenitors so disorders here can greatly reduce RBC production and renewal)
- Hypersplenism (enlarged spleen causes the rapid and uncontrolled destruction of RBCs)
- Acute blood loss (rapid, sudden blood loss means a lower RBC count which can result in anaemia)
- Anaemias of chronic disease (aka anaemias of inflammation, transport of iron is prevented around the body due to things like autoimmune diseases, infections, cancer or kidney failure)
53
What are the different types of macrocytic anaemia?
- Vitamin B12 deficiency (abnormally large RBCs are produced with very limited function, as vitamin helps to form normal RBCs)
- Folic acid deficiency (another b vitamin that helps to make RBCs, deficiency causes failure to produce normal RBCs)
- Liver disease (cholesterol esterification is inhibited in the liver, so more cholesterol is put into the RBC membranes, increasing their surface area, decreasing efficiency of transfer/SA:VOL ratio and lessening deformability)
- Hypothyroidism (can cause all three types of anaemia, causes inhibition of release of EPO)
- Reticulocytosis (increase in immature RBCs seen in the blood)
54
What does MCV stand for?
Mean Corpuscular Volume, refers to the average volume of a RBC (red blood 'corpuscle'), found through multiplying vol of blood by fraction of which is cellular, and then dividing product by the number of erythrocytes present
55
What are the MCV values for the different types of anaemia?
- Macrocytosis: >100
- Normocytosis: 80-100
- Microcytosis: <80
56
What are the different blood groups and how do they work?
Blood group is mediated by different antigens on the cell surface of blood, the ABO and the RhD antigens.
ABO antigens: split into 4 groups, which are
- A
- B
- O
- AB
Where they have A, B, none or both A and B antigens present on their cell surface respectively - all will have antibodies targeting the blood groups NOT present in their blood (e.g. O group has anti-A and anti-B antibodies, B has anti-A, A has anti-B, AB has no antibodies)
These groups are then each split further into two more groups, being either rhesus positive (RhD antigen present) or rhesus negative (RhD antigen not present)
- If RhD is NOT present, then the blood will contain anti-RhD antibodies
These blood groups must be closely matched up to prevent blood being destroyed/rejected by the host due to hostile antibodies present once it has been transfused
- Universal donor (always accepted) is O negative blood, due to it having no antigens present on the cell surface (this blood group can only receive O negative blood however, as their plasma contains antibodies against every other antigen)
- Universal acceptor is AB positive, as the plasma contains no antibodies against any other antigen due to all antigens being present on the RBC membrane surface
57
How many RBCs total are there within the human body and how can this vary?
- Roughly 20-30 x10^12 (20-30 trillion) cells at any one given time, approx. 1/4 of the total human body cell number
- Women have 4-5 million erythrocytes per microliter (ul)
- Men have 5-6 million erythrocytes per microliter (ul)
- People living at high altitudes will have more than this due to hypoxic conditions
58
What are the pathways for haemopoietic stem cells?
```
Forms multipotential stem cell, from this point can either become a myeloid progenitor cell or a lymphoid progenitor cell
Myeloid progenitor cell derivatives:
- RBCs
- Platelets
- Monocytes/macrophages
- Eosinophils
- Basophils
- Neutrophils
Lymphoid progenitor cell pathway:
- B lymphocytes
- T lymphocytes
- Natural killer (NK) cells
```
59
Give a brief outline of immunity.
Innate/natural immunity:
- Not enhanced by previous antigen exposure, essentially always on at the same level
- Encoded within the germline, no memory expressed
- High degree of evolutional conservation
- Key cell types involved are monocytes/macrophages and neutrophils
- Method of immunity includes phagocytosis
- Immune response always has the same peak
Adaptive immunity:
- Previous exposure to antigens results in a faster and bigger response to same antigen if re-exposed
- Memory is present, secondary response receives a big boost
- B and T cell receptors (key) are made by somatic gene rearrangement and somatic mutation, which adds specificity to responses
- Immune response is therefore specific to priming antigen
- Key cell types involved are both T and B lymphocytes
- Method of immunity includes antibody secretion
- Immune response has peaks of increasing size and decreasing time delay on graph
60
How do you carry out density separation with a blood sample?
- Create a test tube with lymphoprep (density gradient medium) below a porous barrier and a whole blood sample above the barrier
- Centrifuge the test tube
- Observe layers: top layer is plasma, then mononuclear/less dense PBMCs (peripheral blood mononuclear cells), then some lymphoprep above and below the porous barrier, and finally with the more dense granulocytes and erythrocytes at the bottom of the test tube
61
What does leukocyte mean?
Translated from Greek, means 'white hollow'
Another term like WBC that encompasses all of the mononuclear cells and granulocytes that make up the WBC constituent of blood
62
What are the granulocytes and what are the mononuclear cells?
```
Granulocytes:
- Neutrophils/PMNs (polymorphonuclear cells)
- Eosinophils
- Basophils
Mononuclear cells
- Monocytes/macrophages
- Lymphocytes (B and T)
```
63
What are the features of neutrophils/PMNs (polymorphonuclear cells)?
- Most abundant leukocyte in blood
- Filled with granules/vesicles
- > mostly lysosomes, fuse with the phagosome to release (hydrolytic/toxic) contents into this structure and break down the ingested material
- Very active migration
- > sensitive to chemotactic factors, attracting them to the site of infection
- Have a characteristic many-lobed nucleus, looks like 'sausages on a string'
- Don't stain strongly with eosin or other basic dyes (not many basophilic structures free within the cytoplasm, so cell stains a neutral pink-ish)
- Raised numbers occur during bacterial infections (extensive reserves which can then be mobilised and progenitor cells are stimulated to divide and differentiate)
- Adhere to vessel walls and transmigrate via diapedesis (passage of blood through capillary cell walls, especially during times of inflammation)
- > engulf bacteria and kill them rapidly with very toxic molecules from lysosomes, with movement of ions into the phagosomes to main conditions (similar action to bleach, very strong oxidisers)
- > will cause collateral damage to host cells, combination of this and the dead bugs results in the formation of pus - 'laudable pus' ('laudable'/praise-able as pus used to be an indicator that enough of a vascular system had been left in the area after surgery)
- > example could be axillary lymphadenitis, where lymph nodes swell massively and become painful due to a bacterial infection
- Engulf, ingest and kill invaders
64
* What defects can effect neutrophils?
- Adhesions molecules
- Killing mechanisms
- > these result in serious pyogenic (pus-forming) infections, e.g. Staph aureus infections, bacterial infection (often on the skin) causes serious skin abscesses, blisters, redness and swelling
65
What is pus?
A thick yellow-white fluid that is the result of infection, accumulation of WBCs, liquefied tissue and cellular debris
66
What are the features of eosinophils?
- Larger than neutrophils
- Stain orange/pink with eosin due to high concentration of basic/positive/cationic proteins (as eosin is negatively charged/acidic)
- Most commonly found in the lungs and the gut
- Controlled by T lymphocytes, acts as an effector cell (short-lived cells that need to be activated to carry out the immune response)
- Elevated levels in the blood after tropical parasite infections (e.g. nematodes/roundworms and other parasites including metazoans (animals with specialised digestive cavity) like hookworm) like hookworms) and after chronic allergic conditions (allergic airway diseases e.g. asthma, involved in the allergic response)
- Contain large, ovoid granules/vesicles which are very electron dense
- Passively absorb IgE antibodies, which provides the cell with specifically shaped receptors to recognise specific antigens, low affinity (therefore requires high concentration) IgE receptors mediate response and exocytosis
- Different molecules can be secreted by eosinophils, toxic and specific to the cell type (e.g. different to neutrophil secretions) which includes eosinophil cationic proteins (ECPs, which are ribonucleases, breaking down RNA transcripts) and eosinophil peroxidases (catalyse redox reactions) -> these cause bad problems if released repetitively into the lungs of asthmatic patients
67
What are the features of basophils?
- Least common type of leukocyte
- Stains with basic dyes
- Has a similar but separate lineage to mast cells (derived from similar progenitors but basophils mature completely in the bone marrow, mast cells mature in the blood stream/progenitors are released)
- Rapidly produce interleukins (glycoproteins secreted by white blood cells during immune response), IL4 and IL13 on activation
- Homologues in blood of the mast cells in tissues
- Component of the inflammatory response to many parasites
- Vesicles/granules contain vasoactive substances such as HISTOMINES (so do mast cells)
- > this is involved in increasing blood flow and vascular permeability during the allergic response
68
What are the general features of monocytes?
- Makes up around 5-10% of WBCs
- Often contain kidney-shaped nuclei
- NO OBVIOUS GRANULES
- Precursor of macrophages in inflamed tissues (macro = big, phage = eat)
- Slower to act than neutrophils
69
Are macrophages blood cells?
No, they are only found within tissues (stationary or mobile during infection)
70
What are the features of natural killer cells (NKs)?
- Contain some scattered granules (gives them another name of large granule lymphocytes)
- Immune surveillance (patrols body looking for 'missing self' cells, which are cells without the necessary 'passport' cell surface antigens and molecules, without these the NK cells will kill the cell it then considers foreign)
- Very important for foetus to survive as an allograft (e.g. derived from the same tissue but not genetically identical) as they aid in protecting foetus from infections and in obtaining blood
- Probably involved in anti-viral immunity (only for some viruses) and maybe also in anti-tumour immunity
71
What are the general features of lymphocytes?
- Most common wbc after neutrophils
- Has subsets
- > T lymphocytes
- > B lymphocytes
- > Natural Killer cells
- No obvious granules
- Vary in size
- Small lymphocytes are memory cells, very dormant and have left the cell cycle (increases longevity), numbers will increase when stimulated (e.g. by secondary infection)
- Large lymphocytes divide rapidly, are known as lymphoblasts and are intermediates prior to full maturation (matured cells will be found both in and out of blood)
- > mature cells in blood: cytotoxic lymphocytes, armed effector cells
- > mature cells outside of blood: antibody-forming cells in tissues
72
* What are some diseases linked to phagocyte deficiencies?
- Chronic Granulomatous Disease (CGD)
- Leukocyte Adhesion Deficiency (LAD I and LAD II)
- Chediack-Higashi Syndrome
- IL-12 gamma-Interferon signalling defects
- Chronic neutropenia (low PNM numbers in the blood)
73
* What is the experiment carried out by J. L. Gowans and what was the result?
- Activated the adaptive response in rats
- Drained rat of lymph
- Showed cells were responding to the specific antigens that had been injected into them in the first place
74
What are the two types of immune response?
- Innate ('natural')
| - Adaptive
75
What are the features of innate immunity?
- 'Always on'
- Not enhanced by previous exposure, so will show no change in height of a response curve during separate infections
- Carried out by leukocytes, not lymphocytes, e.g. monocytes/macrophages, granulocytes and natural killers (less specific responders)
- Respond by recruitment from other blood cells ('activated effector cells, e.g. T lymphocytes)
76
What are the features of adaptive immunity?
- Previous antigen exposure means that a secondary response will be far larger and more effective
- Secondary responses are known as 'memory'
- Response is specific to the antigen that causes the infection and has primed the cells previously
- B and T lymphocytes respond by dividing and differentiating
- > phase 1 is induction (antigen taken up by antigen-presenting cell and expressed, travels to a lymph node or similar area where it is picked up by B and T lymphocytes, presented to receptors on immature helper T cells and cytotoxic T cells with the help of MHC II and MHC I receptors respectively)
- > phase 2 is amplification (T lymphocytes mature and proliferate, helper cells also activate B lymphocytes)
- > phase 3 is effector phase (B lymphocytes secrete antibodies, cytotoxic T cells destroy cells with the same antigens as those presented to them initially)
77
What are the two branches of adaptive immunity?
Humoural
- Antibody mediated
- Uses immunoglobulins (Igs)
- Initiated by B lymphocytes
- B lymphocytes respond and amplify in numbers, develop into antibody forming plasma cells
- B cells require activation from T helper cells before they can secrete antibodies
Cell-mediated
- Controlled by T lymphocytes
- Mainly for defence against intracellular invaders (e.g. viruses)
- Includes action of cytotoxic 'killer' T lymphocytes/cells (shorthand: Tc or CTL), contains CD8 surface molecules that recognise antigens and need to be stimulated for activation
78
Where do lymphocytes first mature?
- T cells mature in the thymus
| - B cells mature in the blood marrow
79
Where is the thymus found?
DO NOT MIX UP WITH THE THYROID
| Found just above the heart, between the sternum and the lungs
80
* What are some diseases linked with lymphocyte deficiencies?
- T cell deficiency: DiGeorge syndrome, caused by abnormal foetal development resulting in specific facial characteristics, congenital heart disease, hypocalcaemia (low calcium levels) and a reduced immune response
- B cell deficiency: Bruton's (Swiss type) agammaglobulinemia, X-linked disease, results in severe antibody deficiency which is characterised in repetitive infections due to absence of mature B cells
- Deficient in both: SCID (severe combined immunodeficiency), combination of several disorders, infants appear healthy at birth but are highly susceptible to serious infections
81
How can B cells producing different antibodies be told apart?
They can't be! Under a microscope, they all look the same - work instead has to be done using antibodies
82
What is clonal selection, expansion and deletion?
- This is where memory B cells expressing a single antigen are amplified to produce antibody-secreting plasma cells
- Only the correct type of antigen-presenting cell is chosen to amplify in response to a secondary infection
- For a primary infection, the theory is that the antibodies become more specific to the antigen as the cell divides due to mutations that prove to be more efficient at binding, this may also occur to some extent during a secondary infection (so would explain faster response time) and is termed clonal selection
- Expansion is the rapid proliferation of cells/formation of daughter cells from the initial lymphocyte
- Clonal deletion is the removal of lymphocytes through apoptosis that express antigens of the host, and so would cause an immune response to tissues within the body containing them (necessary stage during foetal development, remaining self-host cells seen during autoimmune diseases such as type 1 diabetes)
83
* What was the Kohler and Milstein experiment?
1984 Nobel prize for medicine
- Hybridoma technique
- > inject a mouse with antigens that will cause an immune response
- > B cells that produce the antibodies for the antigen are isolated and removed, then made to fuse with an immortal (cancerous) B cell (myeloma) to make a hybridoma, giving it both longevity and antibody-producing capabilities
- > results in the production of monoclonal antibodies (single type of antibody produced)
- Shows that each lymphocyte has only one receptor specificity
84
What are the secondary lymphoid organs?
```
Locations for antigens to encounter lymphocytes, immune reactions occur here to produce more lymphocytes
Includes:
- Lymph nodes
- Spleen
- Peyer's patches
```
85
What are the benefits of lymphocytes patrolling the body constantly?
- Connects functionally dispersed lymphoid tissues (e.g. cells can travel from blood to lymph and back again)
- Only able to leave blood at specific endothelial regions, only on certain venules e.g. within lymph nodes, tonsils, Peyer's patches and other lymphoid organs
- > these filter, process and present the antigen, lymphocytes meet antigens here, not in the blood
- > aid rapid cell division of successful clones as well as maximising chances of useful interactions
- > allow for the fostering of memory
- Ensures that rare clones with a given specificity have a good chance of encountering their specific stimulus (constant circulation)
86
How does Darwinism effect lymphocyte production?
- Huge numbers are created but very few will be chosen
- > ensures that only the best B (+ therefore best antibodies) and T cells will be selected in order to bring about the best immune response
- Does result in substantial cell wastage
