The Immune System Flashcards
What are some examples of myeloproliferative neoplasms?
Polycythaemia vera
- An excess of red blood cells in circulation
Essential thrombocythaemia
- An excess of platelets
Idiopathic myelofibrosis
- Too few RBC, too many platelets and WBC
What are the clinical signs of polycythaemia?
Breathing difficulties Dizziness Excessive bleeding Splenomegaly Headache Itchiness Red colouring (esp. face) Shortness of breath Symptoms of phlebitis
What is thrombosis?
The pathological manifestation of haemostasis
Causes restriction or blockage of blood vessel, causing hypoxia and tissue damage
Thrombi can also dislodge, leading to embolisation
What is haemostasis?
In a physiological state, maintain fluid blood flow within the vasculature
On the vessel injury/trauma, limit/arrest bleeding by forming a clot at the site of injury while maintaining blood flow in the rest of the vessel
Removal of the blood clot following wound healing
What are the risks of Rhesus disease?
Does not effect first Rh+ baby of an Rh- woman but will effect subsequent pregnancies as anti-Rh antibodies will now exist
85% of the population is RhD+; 15% RhD-
Therefore probability of RhD- mother having an RhD+ baby is high
Range in effect - mild anaemia of the newborn to intrauterine death at 18 weeks of gestation (hydrops fetalis)
Kernicterus can also occur in neonates as a complication of severe jaundice which can cause brain damage in severe cases or in mild cases deafness
Relatively rare - alleviated through routine antenatal serology and administration of prophylaxis (anti-D therapy)
- anti-D immunoglobulin will bind and neutralise any RhD+ cells preventing the development of maternal antibodies
What are some features of blood?
One of the four main body fluids (intracellular, interstitial, blood and lymph)
Heart, blood and blood vessels form the circulatory system
Adults have ~5L of blood (4-6L, M>F)
What are the functions of blood?
Transportation:
Supply of oxygen to tissues
Supply of nutrients such as glucose, amino acids, fatty acids
Removal of waste products including CO2, urea and lactic acids
Messenger function - transport of hormones, signalling of tissue damage
Regulation:
Regulation of body temperature
Maintain pH (7.35-7.45)
Hydraulic functions - colloidal osmotic feature
What is the composition of blood?
Two major components: Liquid component - 55% - Plasma Formed elements - 45% - Red blood cells - White blood cells - Platelets
Describe blood plasma.
Yellow/straw coloured liquid portion of blood
Considered the extracellular matrix (ECM) of blood - keeps cells in suspension
Consists of :
Water - 92%
Plasma proteins (albumin, globulins, fibrinogen, prothrombin) - 7%
Other substances (electrolytes, nutrients, hormones, gases, waste products) - 1%
Serum is plasma devoid of clotting factors (achieved by drawing blood in the absence of an anti-coagulant)
What will you see in a test tube if blood is centrifuged?
55% - yellow/straw liquid top layer of plasma
White layer (buffy coat) of white blood cells
45% - red blood cells, red bottom layer, densest layer
What are the formed elements of blood?
Red blood cells - 99%
White blood cells and platelets - <1%
Where are blood cells produced prenatally vs postnatally?
Prenatally:
Yolk sac, then liver and spleen, then bone marrow
Postnatally:
Bone marrow
- Tibia and femur stop production around 20/25
- Production carries on in ribs, sternum, vertebrae and pelvis
Where do RBCs and WBCs migrate to after haematopoiesis?
RBC - blood
WBC - peripheral tissues and lymphoid organs
What are the cytokines and growth factors which tightly regulate haematopoiesis?
Erythropoietin (EPO) - megakaryocyte erythroid progenitor -> erythrocytes
Thrombopoietin (TPO) - megakaryocyte erythroid progenitor -> platelets
Interleukin (IL) - various
Granulocyte colony stimulating factor (G-CSF) - myeloblasts -> basophil/mast cells, neutrophils, - monocytes -> macrophages
Granulocyte macrophage colony stimulating factor (GM-CSF) - most of myeloid progenitor and granulocyte macrophage progenitor
Stromal cell factor (SCF) - various myeloid
What are the cytokines and growth factors which tightly regulate haematopoiesis?
Erythropoietin (EPO) - megakaryocyte erythroid progenitor -> erythrocytes
Thrombopoietin (TPO) - megakaryocyte erythroid progenitor -> platelets
Interleukin (IL) - various
Granulocyte colony stimulating factor (G-CSF) - myeloblasts -> basophil/mast cells, neutrophils, - monocytes -> macrophages
Granulocyte macrophage colony stimulating factor (GM-CSF) - most of myeloid progenitor and granulocyte macrophage progenitor
Stromal cell factor (SCF) - various myeloid
EPO TPO IL G-CSF GM-CSF SCF
What is erythropoiesis, where does it occur and what drives it?
Process of RBC formation
Occurs in bone marrow
Body produces approx 2.5x10^6 RBCs every second
Hypoxia is detected by cells in the kidneys
Kidney cells release EPO into the blood
Erythropoiesis is regulated by EPO binding to the erythropoietin receptor on progenitor cells
EPO-receptor is a kinase linked receptor
What is the pathway of erythropoiesis?
Stem cell (hemocytoblast)
Committed cell (proerythroblast)
Developmental phase:
- Early erythroblast (phase 1 - ribosome synthesis)
- Late erythroblast (phase 2 - hemoglobin accumulation
- Normoblast (phase 3 - ejection of nucleus)
- Reticulocyte
Erythrocyte
What is hemoglobin (Hb)?
Multi subunit polypeptide
4 globin polypeptide chains - 2 alpha and 2 beta chains, each associated with a Haem molecule
Haem molecule composed of porphyrin ring linked to a molecule of Iron as a cofactor
Hemoglobin molecules bind O2 for transportation around the body and CO2 for removal
Iron gives RBC their characteristic colour
What are the features of a red blood cell?
Bi-concave shape related to function
- Optimum O2 transfer
- Flexibility for travel throughout small capillaries
Lifespan of ~120 days
Do not possess repair processes, aged cells are removed by macrophages in the spleen
Abnormal RBCs can be named by their morphology e.g sickle cell anaemia
What is the process of RBCs being broken down by the spleen?
Hemoglobin is separated into Iron and porphyrin ring
Iron transported to bone marrow via transferrin for new RBC production
Porphyrin ring excreted via digestive or urinary tract
- Bilirubin - urine
- Biliverdin - faeces
What is the role of platelets/thrombocytes?
Haemostasis
Initiate blood clotting at site of injury
What is the role of platelets/thrombocytes?
Haemostasis
Initiate blood clotting at site of injury
What is thrombopoiesis and how is it regulated?
Production of platelets
10^11 produced every day
30% are stored in the spleen
Lifespan of 7-10 days
1 megakaryocyte can produce 5000 platelets
Regulated by thrombopoietin (TPO) produced by liver and kidney
Secrete components to aid in repair of vasculature - platelet derived growth factor (PDGF)
What are the steps of thrombopoiesis?
Myeloid stem cell
Megakaryoblast
Megakaryocyte (have platelet precursor extensions coming off it)
Platelets
What is the function of WBCs/leukocytes and how are they classified?
Mediate the protective effects of blood through the generation of the inflammatory process
5 cardinal signs of inflammation - pain, heat , redness, swelling and loss of function
Classifications: Granulocytes vs agranulocytes Polymorphonuclear vs mononuclear Myeloid or lymphoid Innate or adaptive immune system
Which immune cells do you only find in the tissues?
Mast cell
Macrophage
Dendritic cell
Plasma cell
What are the cells of the innate immune system and what are their functions?
Neutrophil: Lifespan ~18 hours 60-70% WBCs Phagocytic - ingest and kill pathogens, debris and damaged cells Initiate inflammatory process
Eosinophil:
Lifespan 2-5 days
2-5% of WBCs
Phagocytic - protection against helminths
Basophil:
Lifespan 1-2 days
0.2% of WBCs
Involved in allergic reaction
Monocyte:
Lifespan 1-7 days
2-10% WBCs
Phagocytic and differentiate to become macrophages within tissues
Natural killer cell:
Lifespan 14 days
15% of WBCs
Killing of virally infected cells
What are the cells of the adaptive immune system and what are their functions?
Lymphocytes: Lifespan weeks to years 20-40% of WBCs B cell (CD19+) CD4+ T cell - helper (CD3+, CD4+) CD8+ T cell - cytotoxic (CD3+, CD8+) All have same morphology so flow cytometry used to identify markers
What is the haematocrit test and what do different results mean?
Centrifuging a blood sample of a specific amount to see the different proportions of plasma, RBCs and WBCs
Normal - ~55% plasma, ~45% RBCs, buffy coat of WBCs and platelets, F = 37-47%, M = 42-52%
Anaemia - Less RBCs, more plasma
Polycythaemia - More RBCs, less plasma
What is a full blood counts purpose and how is it carried out?
Determines properties of blood and blood cells
- Panel of tests investigating different elements
- Good indicator of general health
Use electrical impedance to quantify cell numbers and cell volume
WBC subsets are determined by flow cytometry due to differential cellular properties
What is included in a full blood count?
Hb - hemoglobin RBC - red blood cells MCH - mean corpuscular hemoglobin MCV - mean corpuscular volume Hct - haematocrit WCC - white cell count - Neutrophils (%) - Lymphocytes (%) - Monocytes (%) - Eosinophils (%) - Basophils (%) - Bands (%) (immature form of neutrophils) Platelets Reticulocytes ESR - erythrocyte sedimentation rate EPO (serum) - erythropoietin
What are some disorders of the blood?
Anaemia Myeloproliferative disorders - Polycythaemia (Primary form - polycythaemia vera (PV), Secondary form - essential thrombocythaemia (ET)) - Myelofibrosis or myelosclerosis Jaundice
How many blood groups are there?
8
A, B, AB, O
RhD positive or negative
What is the ABO system?
Blood group A - has A antigens on the RBCs with anti-B antibodies in the plasma
Blood group B - B antigens, anti-A antibodies
Blood group O - no antigens, anti-A and anti-B antibodies
Blood group AB - A and B antigens, no antibodies
O is the most common - 48%
As O has no antigens it can safely be given to any other group
What is the Rh system?
RBCs may have another antigen, a protein known as the RhD antigen
If present your blood group is RhD positive, if not it is RhD negative
e.g A-, B+ etc.
~85% of the UK population is RhD positive
36% - O+
O- can safely be given to anyone as it has no antigens
O- is the universal donor
Why must pregnant women be given a blood test?
If the mother is RhD negative but the child inherits RhD positive blood from the father it can cause complications
Rhesus disease
If the woman become pregnant with an Rh+ fetus again, her anti-Rh antibodies will cross the placenta and damage fetal red blood cells
How are blood types tested for?
Antibodies are added to blood samples and if agglutination takes place the RBC has the matching antigen
What is anaemia?
Anaemia is caused by a reduced number of red blood cells in circulation or a decreased amount of haemoglobin in the red blood cells
This results in reduced levels of oxygen delivery to tissues
This causes weakness, tiredness, inability to exercise and shortness of breath
In some cases this can lead to confusion, thirst and loss of consciousness
Anaemia may be significant before a patient appears pale
What are the signs and symptoms of anaemia?
Signs:
Pallor - especially of the conjunctiva
Tachycardia - pulse over 11 beats per minute
Glossitis - swollen and painful tongue (reasonably specific for vitamin B12 deficiency
Koilonychia - spoon nails (reasonably specific for iron deficiency)
Dark urine - in haemolytic anaemia
Symptoms:
Decreased work capacity, fatigue, lethargy
Weakness, dizziness, palpitations
Shortness of breath - especially on exertion
‘Tired all the time’
In children - decreased IQ, poor concentration, and sleepiness
Rarely - headaches, tinnitus, taste disturbance
More severe disease: Jaundice Splenomegaly Hepatomegaly Angina Cardiac failure Fever
What are the aetiological classifications of anaemia?
The bone marrow
- Suppression
- Infiltration
Problems with iron
- Deficiency at the bone marrow
- Excess absorption
- Ineffective incorporation into haem
Lack of vitamins
- Vitamins B12 and B6
- Folic acid
Anaemia associated with disease in other organs
- Liver
- Kidney
- Reproductive organs
- Connective tissues
- Thyroid
Anaemia due to blood loss
- Haemorrhage
- Trauma (road traffic accident, personal violence e.g. stab wound)
Haemolysis
- Due to antibodies
- Due to drugs
- Infections
Anaemia arising from gene mutation
- Haemoglobinopathy
- Membrane defects
- Enzyme defects
What is the lineage of erythrocytes?
Erythroid
Where do the stages of erythropoiesis take place?
Bone marrow:
Multipotential haematopoietic stem cell -> (regulated by stem cell cytokines e.g. SCF, IL-3 and TPO)
Common myeloid progenitor -> (EPO)
Proerythroblast (pronormoblast) -> (EPO)
Basophilic erythroblast -> (EPO)
Polychromatic erythroblast -> (EPO)
Orthochromatic erythroblast (normoblast) -> (EPO)
Bone marrow and circulating blood:
Polychromatic erythrocyte (reticulocyte) ->
Erythrocyte
How is EPO related to tissue oxygenation?
Blood levels of EPO are inversely related to tissue oxygenation
The level can increase up to 1000x in response to anaemia
What produces EPO?
Juxtatubular interstitial cells of the renal cortex produce 90% of the EPO in blood
They sense oxygen levels through oxygen-dependent prolyl hydroxylase
This regulates the stability of the primary transcription factor for EPO - hypoxia-inducible factor 1 (alpha) (HIF-1(alpha))
Hypoxia increase -> HIF increase -> EPO increase -> RBCs increase (BM) -> Hypoxia decreases -> HIF decreases -> EPO decreases
What are pure red cell aplasias (PRCA)?
Conditions affecting specifically erythropoiesis in the bone marrow
Most common congenital PRCA is Diamond-Blackfan anaemia, which occurs due to reduced proliferation of erythroblasts
Rare condition - occurring in ~5 live births/million
Acquired PRCA can be classified as either primary or secondary
Primary - idiopathic (no clear cause can be identified)
Secondary - acquired as a result to exposure to a pathogenic agents such as a drug or infection
What are pancytopenias?
Conditions affecting other cell types in addition to RBCs (white cells and platelets)
What can cause changes in the bone marrow leading to anaemias?
Congenital - Diamond-Blackfan syndrome, congenital dyserythropoietic anaemia
Infections - Viruses (parvovirus B19, hepatitis B virus, Epstein-Barr virus, mumps, cytomegalovirus, human immunodeficiency virus), bacteria (meningococcal, staphylococcal species)
Malignancy - Solid tumours (such as cancer of the thymus, stomach, breast, lung, thyroid and kidney), haematological tumours (leukaemias, lymphomas, myeloma, myelofibrosis, essential thrombocythaemia, Waldenström macroglobulinaemia)
Autoimmune disease - Systemic lupus erythematosus, rheumatoid arthritis and autoimmune haemolytic anaemia, Sjögren’s syndrome, autoantibodies to red cell progenitors, autoantibodies to Epo, T-cell mediated recognition of red cell progenitors
Other causes - Drug and chemicals (notably azathioprine, methotrexate, gold chloramphenicol, recombinant human Epo and co-trimoxazole), pregnancy, severe renal failure
Many of these conditions cause pancytopenia and aplastic anaemia in addition to red cell aplasia
How do HSCs maintain their population whilst differentiating?
When they replicate, one daughter cell is an HSC (self-renewal) and one is a progenitor cell (differentiation)
This ability may be damaged by insult (chemical, genetic etc.) which eventually leads to HSC exhaustion and pancytopenia
What is haemolytic anaemia?
Caused by the premature destruction (reduced lifespan from ~120 days) of functional erythrocytes either by intrinsic or extrinsic mechanisms
Anaemia develops if the bone marrow is unable to match the rate of destruction by production of new erythrocytes
What are the 2 broadly different reasons for erythrocyte destruction in haemolytic anaemia?
There is nothing fundamentally wrong with the erythrocyte, but they are destroyed by external pathological processes, such as drugs, toxins, autoantibodies or infection
There is something intrinsically wrong with the erythrocyte so it is destroyed, this can be due to damage, absence of certain enzymes or abnormal types of haemoglobin
What is auto-immune haemolytic anaemia (AIHA)?
Autoantibodies are found when a patients’ immune system produces antibodies that recognise their own erythrocytes as foreign and mediate their destruction
Idiopathic AIHA accounts for approximately 50% of cases
Secondary AIHA can result from many other illnesses
Most common causes of secondary AIHA include
- Lymphoproliferative disorders (e.g chronic lymphocytic leukaemia, lymphoma)
- Other autoimmune disorders (e.g. systemic lupus, erythematosus, rheumatoid arthritis, scleroderma, Crohn’s disease, ulcerative colitis)
Drug-induced AIHAs are rare
- Can be caused by a number of drugs, including alpha-methyldopa and penicillin
- Drug binds to macromolecules on the surface of the RBCs and acts as an antigen
- Antibodies are produced against RBCs which leads to complement activation
- This is one type of ‘penicillin allergy’
What is seen on abnormal blood films?
Schistocytes and polychromasia - Fragments of erythrocytes and larger, blue-tinged reticulocytes
Nucleated erythrocytes
Spherocytes - Some cells are very small and termed micro-spherocytes
Can be result of body upping production to maintain normal levels
What are haemoglobinopathies?
Autosomal co-dominant genetic defects resulting in abnormal structure of one of the globin chains of the haemoglobin molecule
Sickle cell anaemia is one of the most common haemoglobinopathies
Sickle cell attributed to mutations in the beta-globin gene
Sickle cell erythrocytes are an abnormal shape, which affects their passage through the circulatory system, their ability to carry O2 and increased haemolysis
Sickle cell anaemia can cause vaso-occlusive crises (vessel blockage), visceral sequestration crisis, aplastic and haemolytic crises
What is haemoglobin, its function and structure?
An iron-containing protein made in erythrocyte cytoplasm
Each erythrocyte contains ~640 million haemoglobin molecules
Designed to absorb O2 from areas of high O2 content (lungs) and release it where the O2 levels are low (tissues)
Consists of a protein part (globin) and a complex non-protein part (haem)
Haem group contains iron which binds to O2 and the globin part consists of 4 globin subtypes
2 alpha chains, 2 beta chains
Each chain includes an iron containing haem group
How can malnutrition and malabsorption cause anaemia?
Essential micronutrients required for various steps in regulating erythrocyte function, especially for the metabolism of haem
- Iron
- Vitamins B6 & B12
- Folic acid
These are obtained in the diet so malnutrition can cause different types of anaemia
Malabsorption may be cause by liver disease, gastric disease or abnormalities in the intestines
Each molecule of haemoglobin must have an atom of iron to which O2 can bind to in the lungs
Therefore a lack of iron directly impacts the amount of O2 that can be transported tot he tissues
How does iron-deficiency anaemia appear on a blood smear?
Characterised by hypochromic (pale) microcytes (small)
RBCs seem to be ‘empty’ with a lack of staining in the centre of the cell
RBCs are also significantly smaller (compare the size of RBCs to the white blood cell in the normal film
How do daily iron requirements change over lifetime?
Infants, adult males and post-menopausal females only require 1 mg
Adolescents require 2-3 mg
Menstruating adolescents require 3-4 mg
Menstruating adults require 2-3 mg
(20-25 mg lost per menstruation)
Pregnancy requires 3-4 mg - (500-1000 mg required overall)
Lactation (amenorrhea likely) requires 1.5-2.5 mg - (also required to repopulate stores
What intestinal factors may contribute to malabsorption?
The stomach: Achlorhydria (lack of HCl) Gastric atrophy Gastritis Alcoholism Gastric carcinoma
Upper and lower digestive tract: Duodenitis Coeliac disease Ulceration Crohn's disease Other inflammatory bowel disease Increased hepcidin levels
Surgery:
Resection of any of the above tissues
What are sources of iron?
High content: Dark-green leafy vegetables Iron-fortified cereals Whole grains Beans Nuts Meat Apricots Prunes Raisins Iron tablets
What is sideroblastic anaemia?
Characterised by failure of iron to be incorporated into haem in the erythrocyte precursor cells rather than lack of iron
Various forms of sideroblastic anaemia that are the consequence of mutations or deletions of genes regulating the expression of key enzymes involved in haem synthesis
A consequence of failure to incorporate iron into the correct areas result in the formation of iron-rich mitochondria which surround the nucleus of the erythrocyte precursor as granules
These cells are termed sideroblasts
What can make iron absorption more difficult?
Tea and coffee Calcium Antacids Proton pump inhibitors (PPIs) Wholegrain cereals (phytic acid)
Why is haem synthesised in erythrocyte precursors and not erythrocytes?
Synthesis requires a nucleus and mature erythrocytes do not have one
What are key regulators of haem production?
Vitamins B6, B12/folate
Deficiencies have significant effects on erythrocyte function
Isolated B6 deficiency is rare in the absence of drugs, particularly the anti-tuberculosis agent isoniazid
B12/folate deficiency is relatively common
What are causes of vitamin B12/folate deficiency and how can it be replaced?
Malnutrition and malabsorption Poverty Pregnancy Drugs Pernicious anaemia: deficiency of gastric intrinsic factor Gastrectomy Small bowel disease Tropical sprue Fish tapeworm Antacids Bacterial overgrowth Pancreatitis
Replacement: Meat Salmon Milk Eggs Fortified breakfast cereals Soy products
How can a deficiency in B12/folate result in a reduction of erythropoiesis?
It is essential for DNA synthesis in erythrocyte proliferation
What are microcytic anaemias and indicators of them?
Iron deficiency:
Mean cell volume <80 (occasionally normal)
Low mean cell haemoglobin
Low ferritin (normal if acute phase response)
Low RBC count
Target cells and pencil cells on blood film
History of bleeding
Anaemia chronic disease: MCV - 70-80 (often normal) Normal MCH Normal or high ferritin Low RBC count No specific features on blood film History of medical disease
Thalassaemia/trait: MCV - Low, often 50-60 Low MCH Normal ferritin High RBC Target cells, poikilocytes, tear drop cells, nucleated red cells on blood film History of ethnic origin
Lead poisoning: MCV - Low or normal Normal MCH Normal ferritin Normal RBC Basophilic stippling on blood film History of exposure
Rare red cell disorders (e.g. sideroblastic anaemia, pyropoikilocytosis): MCV - Low Normal MCH Normal ferritin Low/normal RBC Blood film according to condition Congenital history
How does MCV denote anaemia type?
High - macrocytic
Normal - normocytic
Low - microcytic (further divided by RBC)
What are the different anaemias, by cell size?
Macrocytic: Megaloblastic anaemia Vitamin B12 deficiency Folic acid deficiency Liver disease Hypothyroidism Reticulocytosis
Normocytic: Hemolytic anaemias Bone marrow disorders Hypersplenism Acute blood loss Anaemias of chronic disease
Microcytic: High RBC - Thalassaemias (alpha and beta thalassaemias; or combination with other haemoglobin abnormalities Low or normal RBC - Iron-deficiency anaemia - Lead poisoning - Anaemia of chronic inflammation - Sideroblastic anaemia
Which parts of the bone marrow are responsible for haematopoiesis?
Red marrow - highly vascularised, this is where HSCs reside and therefore where haematopoiesis takes place
Yellow marrow - where adipocytes reside
What are primary lymphoid tissues?
The sites where lymphocytes differentiate to express antigen receptors
- Thymus (T lymphocytes)
- Bone marrow (B lymphocytes)
What are secondary lymphoid tissues?
Specialised sites for turning on the acquired immune response
- Lymph nodes
- Spleen
- Mucosal associated lymphoid tissue (MALT)
(Gut associated lymphoid tissue (GALT))
(Nasal associated lymphoid tissue (NALT))
etc.
Describe the structure of the thymus.
Capsulated (collagen and other extracellular proteins)
Compartmentalisation
- Capsule
- Layer of adipose cells
- Cortex of thymus (very dense lymphocytes)
- Medulla (looks paler on histology - less dense)
- Lobes separated by trabeculae
- Also contains vascular tissue
- Hassall’s corpuscles
Describe the lymphatic system.
A drainage system involved in fluid balance, returning to the blood
- excess interstitial fluid (approx. 3 litres//24h)
- plasma proteins
Lymph capillaries:
Originate as ‘closed tubes’ in almost all tissues (except CNS, epidermis and cartilage)
Capillary wall constructed of overlapping endothelial cells that respond to fluid pressure
Also include valves to stop backflow
Lymphatics:
Lymph capillaries join to form lymphatics
Superficial lymphatics follow superficial veins
- flow into lymph nodes in axillary (armpit), inguinal (groin) or cervical (neck) areas where they drain into deep lymphatics
Deep lymphatics follow main vessels
- lymph nodes either side of aorta (para-aortic) drain the paired organs, nodes lying anterior (pre-aortic) the gut etc
- lymph from 3/4 body drains into the left brachiocephalic vein via the thoracic duct
- lymph from the upper right quadrant enters the right brachiocephalic vein
What is a lymph node?
Important component of host defence
Filter lymphatics
LN represent the anatomical meeting place for cells of immune system an their exposure to antigen
- Arteries transport naive lymphocytes to LN
- Lymph transports antigen
What is a lymph node?
Important component of host defence
Filter lymphatics
LN represent the anatomical meeting place for cells of immune system an their exposure to antigen
- Arteries transport naive lymphocytes to LN
- Lymph transports antigen
Describe the structure of a lymph node.
Lymph drains into LN via afferent lymph vessels
Exit via efferent lymph vessels
Capsulated
Have lobes separated by trabeculae
Has an arterial and venous system to supply lymphocytes
Lymph flows through reticular tissue to germinal centres which are supplied by arteries and veins
Then drains into sinuses and out efferent vessels
LNs vary in size from a pin-head to 1-2 cm
Enlarge during immune response
Lymph nodes of the MALT
- Aggregates of lymphocytes in a reticular mesh
- No incoming lymphatic vessels
- May be isolated or form clusters (Peyer’s patches in ileum; tonsils)
What is the function of the spleen?
Largest lymphoid organ
Receives lymphocytes and antigens via bloodstream
Directs immune responses to antigens in the blood
Important for clearance of effete red blood cells
Hyposplenism or asplenia not fatal, but predisposes to infection (especially of capsulated bacteria)
Presence of Howell-Jolly bodies (erythrocytes with nuclear fragments) in peripheral blood is often diagnostic of hyposplenism/asplenia, as normally cleared by spleen
Splenomegaly common in chronic disease (malaria, leishmaniasis, Hodgkin’s disease)
What is the function of the spleen?
Largest lymphoid organ
Receives lymphocytes and antigens via bloodstream
Directs immune responses to antigens in the blood
Important for clearance of effete red blood cells
Hyposplenism or asplenia not fatal, but predisposes to infection (especially of capsulated bacteria)
Presence of Howell-Jolly bodies (erythrocytes with nuclear fragments) in peripheral blood is often diagnostic of hyposplenism/asplenia, as normally cleared by spleen
Splenomegaly common in chronic disease (malaria, leishmaniasis, Hodgkin’s disease)
What is the location and size of the spleen?
Left hypochondriac region of abdominal cavity
Normally 12 x 7 x 2.5 cm and 0.2 kg
Accessory spleen may be present in 10% of population
What is the microanatomy of the spleen?
Red pulp with round white pulp in it (bunch of grapes in red jelly)
Looks like a collection of many lymph nodes
Non-immune functions in red pulp
White pulp effectively the same as a lymph node
Spleen is capsulated but individual white pulp is not
How do lymphocytes know which compartment to migrate to?
B and T lymphocytes has different chemokines they are attracted to and these are sequestered into zones
Follicle (B area) - CXCL13
T cell zone - CCL19 and CCL21
What produces the chemokines which contribute to the compartmentalisation of lymphoid tissues?
Stromal cells (non-haematopoietic)
- Blood endothelial cells
- Fibroblastic reticular cells
- Lymphatic endothelial cells
How many systems are there for classifying blood types?
30
Based on a number of characteristics; cell surface and/or soluble antigens
2 main are ABO and Rh (Rhesus)
If undergoing longterm treatment people will be tissue typed more closely using the other systems
What are the A and B antigens?
Carbohydrate structures present on red cell membrane glycoproteins and glycolipids
The major carriers of A and B on red cells are the abundant N-glycosylated glycoproteins, the anion exchanger (band 3) and the glucose transporter (GLUT1)
Gene encodes glycosyltransferase
- Type A - N-acetylgalactosaminyltransferase
- Type B - Galactosyltransferase
- Type O (H) - no transferase
How are the ABO blood groups inherited?
Encoded by one gene on Chromosome 9
3 allelic variants
Isoagglutinogen (antigen) - i, IA and IB
Not Mendelian inheritance
IA and IB are co dominant while i is recessive to both IA and IB
4 blood groups; A, B, AB and O
Multiple genotypes giving rise to phenotype
What is the Rh blood group?
Most complex blood group system
5 major Rh antigens - D, C, c, E, e - most immunogenic is D
Encoded by two genes RHD and RHCE
Individuals can be homozygous for RHD (2 copies) or hemizygous (1 copy - other may be deleted), all express D antigen on RBC
Individuals where RHD is deleted have no expression of D antigen - both copies deleted
Individuals are RhD+ or RhD-
No anti-D antibodies present in blood
What are the risks of Rhesus disease?
Does not effect first Rh+ baby of an Rh- woman but will effect subsequent pregnancies as anti-Rh antibodies will now exist
85% of the population is RhD+; 15% RhD-
Therefore probability of RhD- mother having an RhD+ baby is high
Range in effect - mild anaemia of the newborn to intrauterine death at 18 weeks of gestation (hydrops fetalis)
Kernicterus can also occur in neonates as a complication of severe jaundice which can cause brain damage in severe cases or in mild cases deafness
What is the universal recipient and the universal donor?
AB+ - recipient
O- - donor
What are the genetic anaemias?
Haemoglobinopathies
- Sickle cell disease - change in quality of the beta globin chain
- Thalassaemia - caused by a reduction in quantity of the alpha or beta globin chain
What is the cause of sickle cell anaemia?
Mutation of the HBB gene - glutamic acid replaced by valine
Gene form termed HBS
Alters Hb affinity for O2
Under deoxygenated conditions Hb tetramers with a mutated beta-globin chain have the tendency to complex forming polymers which cause distortion of the RBC - ‘sickle’
Individuals with only one copy of mutated beta-globin gene are able to complex but less efficiently
2 A genes, Haemoglobin AA, no disease
A/S genes, Haemoglobin AS, SC trait
2 S genes, Haemoglobin SS, SC disease
What is the inheritance pattern of thalassaemia?
Similar to sickle cell
Multiple genes depending on the form of thalassaemia
A child can only have the disease if both parents have the disease gene
What is the incidence of sickle cell anaemia?
Most prevalent in Sub-Saharan Africa, Middle East and India
Most prevalent in individuals of African or Caribbean descent
What is the prevalence of thalassaemia?
Most prevalent in individuals of Mediterranean, South Asian, Southeast Asian and Middle Eastern origin
What disease has a relationship with sickle cell anaemia?
Malaria
Incidence correlates with endemicity of Plasmodium falciparum
Haemoglobin AS has a selective advantage in parts of the world with endemic malaria
Relative protection from dying from malaria: selective advantage
Sickle cell anaemia (SS) gives a worse outcome for malaria
AS population far higher than SS
How does sickle cell anaemia present?
Episodes of severe haemolytic anaemia
Vaso-occlusive episodes - crises with possible infarcts in bones, lung, spleen, brain
Infections
Sickle cell trait may present with minor symptoms
Debilitating condition - impacts on individual in a personal nature in addition to social/familial context
- impact on daily life, relationships, reduced lifespan; implications for having a family
What is the clinical management of haemaglobinopathies?
Genetic anaemias are a major disease burden, most common hereditary disorders in the world
Estimated that 1000 people in UK have thalassaemia, and between 13,000-15,000 people in the UK have sickle cell
Disease management :
Prophylaxis - reduce risk of infection e.g. pneumococcal vaccination, folic acid supplements, prophylactic penicillin, spleen size determination, lifestyle modification
Bone marrow or stem cell transplant may be curative but risky treatment, not a common approach
Management - may include blood transfusions at intervals
Prevention - genetic screening, antenatal screening of parents and postnatal screening of baby
NHS sickle cell screening programme
Education - genetic counselling and support to manage disease, Sickle Cell Centre
Why do we have innate defences?
Innate immunity may prevent pathogen establishment
Innate immunity may limit pathogen multiplication
Innate immunity provides protection from early death during the expansion phase of the acquired immune response
Innate immunity helps to ‘instruct’ the nature of the acquired immune response generated after infection
What are non-immunological barriers to infection?
Skin:
Mechanical - Epithelial cells joined by tight junctions, longitudinal flow of air or fluid
Chemical - Fatty acids, antibacterial peptides
Microbiological - Normal flora
Gut:
Mechanical - Tight junctions, flow of air
Chemical - Low pH, enzymes (pepsin), antibacterial peptides
Microbiological - Normal flora
Lungs:
Mechanical - Tight junctions, movement of mucous by cilia
Chemical - Antibacterial peptides
Eyes/nose:
Mechanical - Tight junctions
Chemical - Salivary enzymes (lysozyme)
What are the three pathways of the complement cascade?
Classical pathway:
Antigen:antibody complexes (pathogen surfaces)
MB-Lectin pathway:
Mannose-binding lectin binds mannose on pathogen surfaces
Alternative pathway:
Pathogen surfaces
What are the functions of protein classes in the complement system?
Binds to antigen:antibody complexes and pathogen surfaces -C1q Binding to mannose on bacteria - MBL Activating enzymes - C1r, C1s, C2b, Bb, D, MASP-1, MASP-2 Membrane-binding proteins and opsonins - C4b, C3b Peptide mediators of inflammation - C5a, C3a, C4a Membrane-attack proteins - C5b, C6, C7, C8, C9 Complement receptors - CR1, CR2, CR3, CR4, C1qR Complement-regulatory proteins - C1INH, C4bp, CR1, MCP, DAF, H, I, P, CD59
How do pattern recognition receptors identify pathogens?
By recognising pathogen associated molecular patterns (PAMPs)
What ligands are recognised by which Toll-like receptors (TLRs)?
TLR-1 dimer, TLR-2/TLR-6 dimer: Peptidoglycan (Gram +ve) Lipoproteins Lipoarabinomannan (mycobacteria) GPI (T. cruzi - parasite) Zymosan (yeast)
TLR-3:
dsRNA (virus)
TLR-4 dimer (plus CD14):
LPS (Gram-negative bacteria)
TLR-5:
Flagellin
TLR-9:
Unmethylated CpG DNA
What are the principles of phagocytosis?
Attachment by pattern recognition receptors
Pseudopodia forming a phagosome
Granule fusion and killing (complete formation of the phagolysosome)
Release of microbial products
What is the respiratory burst?
When NADPH oxidase is activated and releases toxic oxygen radicals (superoxide and hydrogen peroxide)
Oxygen radicals may directly damage microbial membranes and/or activate microbicidal enzymes found in granules
How does the role of the phagosome differ between innate and adaptive immunity?
Innate: Pathogen killing 'Pathogen processing' 'Pathogen presentation' - TLRs 'Pathogen presentation' to cytosolic sensors - NODs/NALPs
Adaptive: Antigen degradation Antigen processing Antigen presentation - MHCII Antigen presentation via cytosol - MHCI
What are the microbicidal mechanisms of phagocytes?
Acidification
- pH~3.5-4.0, bacteriostatic or bactericidal
Toxic oxygen-derived products
- superoxide O2-, hydrogen peroxide H2O2, singlet oxygen 1O2., hydroxyl radical OH., hypohalite OCl-
Toxic nitrogen oxides
- Nitric oxide NO
Antimicrobial peptides
- Defensins and cationic proteins
Enzymes
- Lysozyme (dissolves cell walls of some Gram-positive bacteria), acid hydrolases (further digest bacteria)
Competitors
- Lactoferrin (binds Fe), vitamin B12-binding protein
What are the frequencies of phagocytes in blood?
Neutrophil - 40-75% Eosinophil - 1-6% Basophil - <1% Monocyte - 2-10% (Lymphocyte - 20-50%) Dendritic cells - <1%
What are neutrophils?
(Polymorphonuclear neutrophils; PMNs) Rapid responders Mobilised from BM by GM-CSF Found in 'depots' in tissue sites Highly phagocytic Produce multiple cytokines
How to activated neutrophils catch bacteria?
Neutrophil extracellular traps or NETs Contain: Chromatin Granule proteins Enzymes to degrade pathogen virulence factors
What do blood monocytes give rise to?
Tissue macrophages
Monocytes are phagocytes in their own right
HSC-derived monocytes and macrophage are:
A diverse and complex group of cells
Have varied differentiation pathways during inflammation
Share many functions
Relatively long lived
Host cells for many pathogens (e.g MTB)
Most tissue macrophages arise from non-haematopoietic precursors
What are the resident macrophages in the liver?
Kupffer cells
Embryonic yolk sac derived ‘resident macrophages’ have specific
- forms and functions in different tissues (inc. homeostasis)
- transcription factors and epigenetic mechanisms associated with development
- responses to environmental cues
What are dendritic cells?
Phagocytes specialised for interacting with lymphocytes
Complex subset of myeloid cells
- defined by specific TFs and cells characteristics
- can be sedentary or migratory
- are activated during innate immunity
- play an important role in initiating immune responses
How do cells move from blood to tissue?
Extravasation:
Monocyte binds adhesion molecules on vascular endothelium near sites of infection and gets chemokine signal
The monocyte migrates into the surrounding tissue
Monocyte differentiates into a macrophage and migrates to the site of infection
Pathways of cell recruitment
- links multiple aspects of immune cell biology
- an essential component of inflammation and immunity
- a key target for therapeutic manipulation
What are cytokines and chemokines?
The hormones of the immune system
Allow communication between a variety of immune and non-immune cells
>30 identified, with specific but overlapping functions
Mostly referred to as ‘interleukins’ hence IL-1, IL-2, IL-3 etc, but some use ‘functional names’ e.g ‘tumour necrosis factor’ (TNF)
A further heterogenous and complex family of small molecular weight chemotactic cytokines are known as ‘chemokines’ (>30)
What are key features of cytokine and chemokine regulation?
Mostly short acting ‘hormones’ but can have systemic effects e.g. in shock
May be released in a polar fashion at ‘synapses’
Recognised on target cells by specific receptors (with some redundancy)
Receptor expression is highly regulated to control the targets and duration of response
Subsets of cytokines/chemokines may be selectively co-regulated and help define cell subsets e.g Th1 and Th2 CD4+ lymphocytes
What aspects of immune functions can be affected by steroids?
Corticosteroid therapy:
Decreases IL-1, TNF-alpha, GM-CSF, IL-3, IL-4, IL-5, CXCL8
- decreases inflammation caused by cytokines
Decreases NOS
- decreases NO
Decreases phospholipase A2 and cyclooxygenase type 2, increase lipocortin-1
- decreases prostaglandins and leukotrienes
Decreases adhesion molecules
- reduced emigration of leukocytes from vessels
Increased endonucleases
- induction of apoptosis in lymphocytes and eosinophils
How does activation of a macrophage lead to different responses?
Classical activation (IFN-gamma, TNF, IL-1): Type 1 immunity - microbial killing, tissue damage, DTH
Alternate activation (IL-4/IL-13, IL-10, GM-CSF): Type 2 immunity - allergy, helminth responses, fibrosis and repair
What are natural killer cells?
Atypical ‘innate’ lymphocytes
What are the three stages of haemostasis?
1 - Vascular spasm - damaged blood vessels constrict, reducing blood flow in the damaged area
2 - Platelet plug formation - (primary haemostasis) platelets bind to the damaged vessel wall and form a platelet plug
3 - Coagulation - (secondary haemostasis) a stable clot forms by converting fibrinogen to fibrin
What are platelets?
Platelets are small (2-3µm) fragments of megakaryocyte cytoplasm
A healthy adult produces ~10^11 platelets/day, the physiological range is 150-400x10^9/L of blood
Platelets circulate in the blood and have a lifespan of ~5-9 days, old platelets are destroyed by Kupffer cells in the liver or by phagocytosis in the spleen
What are the secretory granules of platelets?
alpha-granules
Dense-granules
What is the ultrastructure of the platelet?
No nucleus, platelets contain all the factors required for their function
Critical components are:
- Membrane proteins
- Secretory granules
- Surface-connected open canalicular system (SCOCS)
Surface-connected canalicular system Microtubules alpha-granule Dense granule Glycogen Mitochondrion
What are alpha-granules?
Most prominent and numerous (50-80/platelet) and are 200-500nm in size
Contain:
- Adhesive proteins (fibrinogen, fibronectin, vWF)
- Platelet-specific proteins (PF4, PDGF)
- Membrane proteins (GPIIaIIIb, GPIb/IX/V)
- alpha-granule-specific proteins (P-selectin)
What are dense-granules?
2-7 dense granules/platelet, 2-300nm in diameter
Electron dense when stained with osmium tetroxide, dense core with a halo
Dense-granules contain:
- Vasoconstrictive agents (serotonin)
- Platelet agonists (ADP, ATP)
- Calcium and magnesium
What are the platelet membrane proteins?
- Receptors for various agonists (ADP, thrombin, TXA2)
- GPIb-IX-V complex - GPIbα, GPIX, GPIβ, GPV (vWF interactions)
- GPIIb-IIIa complex - GPIIIa, GPIIb (vWF interaction, fibrinogen binding and platelet aggregation)
- GPIa-IIa complex - GPIa, GPIIa (collagen interactions)
- GPVI (collagen interactions)
