Module 4 (blood and immune) Flashcards
Blood volume and circulation
5L in humans; 14,000L through the heart every 24 hours; must be maintained to retain pressure
Blood overall function
Provides a one-way pressurised system for the transport of oxygen, proteins, lipids, glucose and essential ions required for normal cell function; bathes muscles and other organs in an oxygenated environment
Arterial pressure
Maintained by elastic vessel walls that contain lots of smooth muscle; very high pressure because walls expand to carry systolic pressure from the heart
Venous pressure
Lower pressure, veins are not elastic; one-way valves required to prevent back-flow and ensure it if always flowing in one direction
Blood loss
People can withstand up to 20% of blood loss; any more results in pressure and flow being impaired and tissue is starved of oxygen
Hypertension
High blood pressure; can be caused by a narrowing or hardening of the arteries, reducing flow and resulting in unwanted coagulation
Circulatory system components
Heart (L and R ventricles and atria); capillaries (large: high volume/low flow; small: low volume/high flow); veins and arteries
Blood pressure; changes and function
Different depending on the vessel type; normal BP is 120/80 (120mL mercury -systolic blood pressure)
High BP - arteries not expanding and contracting efficiently - something wrong and significant use to thromboses
Low BP: not enough blood pumping through veins to supply muscles and tissue with oxygen
Ensures even and efficient blood flow through the small capillaries; it is low enough to prevent capillary leakage but high enough to avoid coagulation.
Systolic pressure
Blood is at full compression (LV is squeezed at highest and arteries are expanded at greatest); 120/80 BP
Diastolic
The heart is at complete rest
Major components of blood (6)
Cells (erythroid, myeloid and lymphoid)
Proteins (major types: albumin, haemoglobin, fibrinogen, immunoglobulins)
Lipids (bound in lipoproteins; HDL, LDL and VLDL)
Electrolytes (salts and minerals; HCO3-, Na+, Cl-, Ca++, Mg++, K+, creatine, creatinine)
Vitamins, hormones
Glucose
Erythroid cells
Erythrocytes; solely for oxygen transport; don’t have a nucleus so survive radiotherapy much better (no DNA)
Myeloid cells
Neutrophils, monocytes (become macrophages), basophils, eosinophils); all white blood cells which engage in some form of innate immunity (and sometimes phagocytosis); they have a range of receptors that bind immune complexes
Composition of types of cells in the blood
Erythrocytes: 5-6 million/mL
Leukocytes: 10,000/mL
Platelets: 400,000/mL
Lymphoid cells
B-cells (come from bone marrow; provide antibodies/immunoglobulins; adaptive immunity)
T-cells (migrate to the thymus above the heart and become a part of the cellular adaptive response)
Albumin
Most abundant protein (accounts for ~50% of total blood protein); functions mainly to maintain colloidal osmotic pressure (to provide a soak for fluid within the blood - preventing leaking from capillaries) and also binds and transports many small molecules and proteins, maintains hypertonicity
Fibrinogen
Second most abundant protein - cleaved by the enzyme thrombin (in the coagulation cascade) to form cross-linked fibrin that forms the blood clot - prevents leakage; constitutes 7% of total blood protein
Immunoglobulin
(Ig) AKA antibody; found in the gamma fraction in serum electrophoresis), responsible for immunity; produced by plasma cells (a form of B lymphocyte); constitutes ~10% of total blood protein and becomes elevated in diseases such as multiple myeloma; provide us with a vast repertoire of different antigen-binding molecules which provide defence against everything
Complement proteins
A set of 9 plasma proteins that phagocyte and opsonise foreign organisms; innate immunity; most abundant protein is C3; essential for tagging/coating invading organisms so they can be digested
When they encounter bacteria with a surface different enough, it is activated
Coagulation factors
A set of 13 proteins cleaved in an ordered cascade that initiates the cleavage of fibrinogen into fibrin to form the clot; thrombin is the central enzyme that cleaves fibrinogen; Ca++ essential to coagulation
Haemoglobin
The major component of RBCs which carries oxygen from lungs to the heart to tissue; constitutes 96% of RBCs dry weight which makes up ~45% of the blood volume
Each molecule contains 4 haem molecules each containing 1 iron atom (in feris state); can carry 4 oxygen molecules each
Oxygen loaded, transported to the tissue where it dissociates (due to partial pressure of oxygen reducing), picks up a CO2 molecule and removes it
Missing coagulation component
Haemophilia’s result; factor VIII deficiency is the commonest form
Electrolytes
Salts and minerals that maintain isotonicity and buffering; free Ca++ and K+ also tightly maintained - crucial for the regulation of membrane channels, ion pumps and normal nerve and muscle function (such as the heart)
Deviation from any of the normal levels of ions will result in a significant illness
Oxygen transport conditions
Many molecules can displace O2 from Fe++
CO2 - venous blood
CO - carbon monoxide poisoning
CN - cyanide poisoning
Lipids
Taken up when a fatty meal is eaten; transported by lipoproteins; based on density (the only way to isolate them is to centrifuge them at a high speed - they have a very low density and float to the top of the centrifuged blood)
LDL - low-density lipoproteins (bad lipoprotein)
HDL and VLDL (good lipoproteins)
The ratio of LDL:HDL is tested for when doctors do a lipid screen
Vitamins and hormones
Transported to various organs by blood (insulin, glucagon, fertility hormones)
Blood homeostasis
Maintaining a stable blood acid/base balance is very important; blood pH is very tightly maintained at 7.4 with a variance of 0.2 - any more could result in severe stress (acidosis or alkalosis); effectively buffered by albumin, phosphate, bicarbonate, creatine and other compounds
Centrifugation of blood
The most simplified form of separating blood; separates into 3 components (packed red cells 40%, buffy coat containing white blood cells and platelets 10% and plasma containing soluble proteins and lipids 50%)
Blood clots are removed and serum leftover (without fibrinogen because they formed the insoluble fibrin clot, and other cells)
Medical test for health looks at packed RBCs (can have too many or too little) - too little could lead to cerebral Dema
Plasma
The viscous liquid fraction of blood without cells (uncoagulated blood); contains fibrinogen that is removed with coagulation
Doesn’t tend to electrophorese very well due to the fibrinogen causing problems with the process - needs to be removed with the clot
Serum
The less viscous yellow liquid remaining after clot removal; normally straw yellow but after a fatty meal it will be cream coloured due to the lipid ingested
Serum electrophoresis define
A common means of separating blood proteins using an electric field (electric current); separates serum into 5 major protein fractions: albumin (~50%) and globulin (alpha1, alpha2, beta and gamma add to ~40% - immunoglobulins)
Multiple myeloma
Form of leukemia where a malignant lymphocyte produces monoclonal Ig; serum electrophoresis is used to diagnose the condition; single band appears in gamma globulin fraction, which indicates there is a B-cell over-producing a monoclonal antibody
B-cell malignancy (aberrant B-cell becomes malignant), it is mature so produces an antibody in high amounts; patient develops monoclonal antibody in their blood
When it becomes advanced, the antibody is in such high concentration that it is urinated
Serum electrophoresis method
The serum is mixed with a buffer solution to regulate the pH; blood proteins are dapped on paper/carrier and an electric field is applied (+ and - electrodes); proteins are charged and with travel to either electrode - spread of blood proteins
Albumin in serum electrophoresis
It is a negatively-charged protein so will migrate toward the + electrode (the density is measured and the spikes show a scan of the stain)
Gamma fraction in serum electrophoresis
Gamma globulin fraction carries immunoglobulins or antibodies; migrate furthest to the negative electrode (due to their + charge)
The simplest technique to identify someone who has an abnormality
Hemocytoblast
All blood-circulating cells come from this single multipotent human stem cell (HSC) found in the bone marrow; extremely rare (about 1 in 10,000 WBCs are CD34+); characterised by the CD34 cell surface marker antigen to isolate these cells
CD34+ HSC give rise to myeloid or lymphoid progenitors (multipotent stem cells)
There is a high concentration in the umbilical cord blood
Autologous HSC transplants
Stem cells saved from birth can save the child
Treat leukemia using radio oblation and chemical oblation, transplant the core blood into the patient so the HSC will repopulate the bone marrow and generate a normal blood system
Can also be used in adults
Isolate the cells using monoclonal antibodies which recognise the CD34 antigen - has a fluorescent tag/magnetic bead; when added to the patient’s blood can isolate the HSCs; treat them with radiation to destroy the WBCs and their ability to make WBCs - hopefully destroying leukemic cells as well; transplant back CD34 cells
Myeloid lineage
The myeloid progenitor gives rise to erythrocytes, megakaryocytes, mast cells or myeloblasts (innate immunity)
Megakaryocytes –> thrombocytes
Myeloblasts –> neutrophils, basophils, eosinophils or monocytes (–> macrophages)
Lymphoid lineage
The lymphoid progenitor differentiates into natural killer cells or lymphocytes
B-lymphocytes (make antibodies; give rise to plasma cells)
T-lymphocytes (generated through the thymus gland; immature cells differentiate into CD4 or CD8)
Haematopoiesis and factors
Differentiation process of cells; GM-CSF, EPO and G-CSF
GM-CSF
Granulocyte macrophage colony-stimulating factor; produced by macrophages, T-cells, endothelial cells and fibroblasts; stimulates the production of neutrophils, eosinophils, monocytes and basophils
Administered to re-populate white cells in leukemia patients following radio-ablation
EPO
Erythropoietin; drives the production of erythrocytes; produced mainly by the kidney during adulthood and liver in perinatal
Favourite drug of performance athletes; more RBCs transport more O2 to tissues; also allows high-altitude training
G-CSF
Granulocyte colony-stimulating factor; produced by many different cells; stimulates the production of granulocytes but also acts as mature neutrophils
Administered to re-populate white cells in leukemia patients following radio-ablation
Oxygen transport and exchange; alveoli and arteries
Getting oxygen to tissues so oxidative phosphorylation can occur (ATP production)
Alveoli: very thin membrane for diffusion; wrapped in tiny capillaries so when blood comes through the capillary network it can pick up oxygen
Arteries reside very deep in tissue a run along bones; damage would result in rapid loss of blood (because they are under pressure)
Classical activation
Initiated by antibodies binding to the surface of a microbe; C1, C2, C4 and C3 condense on the antibody to form a bound C3 convertase on the microbe surface; mediated by IgM or IgG binding to a microbe surface which is then bound by C1
Lectin activation
Lectins are carbohydrate-binding proteins in the blood which bind to unusual carbohydrates found only on microbes; complement condenses on these bound lectin
Alternative activation
Complement C3 is activated just by being close to the surface of the microbe; this activates another type of C3 convertase
Complement and innate immunity
When complement is activated, there is a cascade pathway; includes the classical, lectin and alternative pathways, end-stage complement, anaphylatoxins and phagocytic cells
End-stage complement
The surface-bound convertases activate complement C5-9; forms a pore (MAC - membrane attack complex) that inserts into some bacterial membranes to cause lysis
Anaphylotoxins
Small polypeptides generated by cleavage of the larger complement proteins (C3, C4 and especially C5); powerful chemoattractant (C3a, C4a and C5a) that recruit and activate phagocytes (neutrophils) to the site of infection
Phagocytic cells
Neutrophils and macrophages have complement receptors that bind complement and initiate phagocytosis
Opsonisation
Deposition of complement on microbes; essential for phagocytosis
Convertases
Deposited complexes on microbes activate more complement that then deposits to coat the surface; irreversibly bound to through a covalent bond
Inhibition of the complement cascade
Many microbes produce proteins (virulence factors)
People with deficiencies in a complement component are susceptible to chronic infections
Coagulation pathway
Proteolytic activation cascade that can be initiated through the intrinsic or extrinsic pathway; tissue damage or surface contact results in the binding and activation of platelets that bind to the vessel cell wall
Calcium is essential
Intrinsic pathway
Contact;
Factors XIII, XI, IX and VIII (12, 11, 9, and 8) lead to the cleavage of factor X (10); converts prothrombin to thrombin
Extrinsic pathway
Tissue damage; Factors VII (7) and tissue factors (TF) combine to activate factor X
Factor X
Activates thrombin; common in both coagulation pathways
Thrombin; blockage
An enzyme that cleaves fibrinogen to fibrin which cross-links to form a blood clot
Anti-coagulants can block thrombin; heparin and warfarin are used in medicine and many insects and parasites that rely on blood for food produce them
Plasminogen; streptokinase and TPA
Protease that is activated by tissue plasminogen activator (TPA) or streptokinase; plasmin (active) cleaves the fibrin clot (dissolves it) resulting in thrombolysis
TPA and streptokinase are important as they are used to treat unwanted blood clots (myocardial, PE, DVT, etc.)
Innate immunity
All animals - more primordial that adaptive; recognition of traits shared by broad ranges of pathogens, using a small set of receptors; provided by myeloid cells; rapid response - immediate and first line of defence against an infection
Anatomical and physiological barriers
Intact skin, mucous membranes, secretions (ciliary clearance; lysozyme in tears and saliva); low stomach pH
Innate cellular response
Natural killer cells, neutrophils, eosinophils, macrophages, mast cells, dendritic cells
Innate humoral response
Complement, mannose-binding lectin (activate complement; recognises unique carbohydrates found on the surface of bacteria), LPS binding protein, C-reactive protein, antimicrobial peptides (bind to the surface of bacteria; in parts of the body that come into contact with the environment)
Adaptive cellular response
T-cells, B-cells
Adaptive humoral response
Antibodies
Humoral system and response
Soluble proteins that exist in the blood, designed to opsonize the microorganisms; antimicrobial peptides that directly kill bacteria and antibodies (produced by B lymphocytes)
3 processes of innate immunity in mammals
Complement (C’) - opsonisation of microbes by blood proteins and the production of anaphylatoxins that attract and activate phagocytes
Phagocytosis (myeloid cells - neutrophils and macrophages) - engulfment of the microbe by phagocytes that destroy the organism
Pattern Recognition Receptors (PRR) - receptors found on many myeloid cells that recognise complex microbial molecular patterns
Normal immune system and malfunction
Usually able to distinguish when it sees something that is not a part of the self-system, kept in a state of tolerance by a range of mechanisms; in both innate and adaptive responses, the system is tolerant to itself
If it is broken, an autoimmune disease occurs (the immune system goes wrong and attacks own cells - e.g. type 1 diabetes)
Gene-editing technology
CRISPR/Cas9 technology is the latest development; insert collections of genes into cells and design the sequence to represent that of a specific gene wanted to be edited; used to develop therapeutics to combat cancer
Viruses
Intracellular pathogens that host cell machinery for replication; defence relies on cellular immunity - needs to be able to distinguish infected from normal cells; will infect epithelial cells of the nose, pharynx or upper respiratory tract (or lungs), capture the machinery to make copies and the cell is destroyed
Bacteria, yeast and fungi
Predominantly extracellular pathogens that are engulfed and destroyed by phagocytic cells; most can be distinguished by the Gram stain (stains cell wall found on most bacteria); good at developing resistance
Gram-positive (bacteria)
Have a thick peptidoglycan cell wall as a defence; requires phagocytosis and are not killed directly by complement
Gram-negative (bacteria)
Have a thin peptidoglycan layer surrounded by an outer membrane; can often be lysed directly by complement Membrane Attack Complex
Protozoa and other parasites
Complex multicellular organisms, highly developed; can live inside or outside cells; too big to be engulfed by macrophages; basophils, eosinophils and mast cells secrete inflammatory mediators and cytotoxic chemicals that kill; immune response typically includes innate, adaptive and action of the innate immune cells to directly kill the organisms
Neutrophil response
Rapid response to infection; they move from the confines of blood capillary, through the capillary wall and migrate between cells to the site of infection; highly coordinated processes are opsonisation, chemotaxis and phagocytosis
Microbes produce inhibitors that block nearly every step of this process
Neutrophil extravasation and chemotaxis
- Activation - chemokines from tissue injury activate the endothelial cells lining the inside of the adjacent capillaries
- Tethering - neutrophils slow and tether to the activated endothelial cells inside the capillary wall
- Adhesion - strong binding between neutrophil integrins and ICAM-1 on the endothelium; neutrophil flattens out
- Diapedisis - neutrophil finds a junction in between two endothelial cells, squeezes between them and out of the capillary into the tissue
- Chemotaxis - neutrophil migrates along a chemokine gradient to the site of infection
Opsonisation
Process of covering microbes with complement proteins to form complex convertases ready for phagocytosis; neutrophils and macrophages engulf opsonised bacteria but ignore non-opsonised cells
Types of convertases
Classical, lectin, alternative pathway
Neutrophils in opsonisation
The leading side of neutrophil detects chemoattractants of complement (such as C5a) released from the surface of bacteria; migrate up the chemoattractant gradient, polymerising actin filaments at their leading edge and de-polymerizing them at their trailing edge; they have receptors which bind deposited complement proteins (mainly C3b) on the surface
Complement receptors
Myeloid cell receptors that bind activated complement components deposited on bacteria; CR1 is the main neutrophil receptor and binds to C3b; cross-linking of the surface CRs initiates phagocytosis
FcR (antibody) mediated phagocytosis
- Antibody (IgM and IgG) bind to antibacterial antigens
- Exposes the antibody Fc region
- Neutrophil FcR binds multivalent Fc
- Activates phagocytosis
- Membrane invaginates forming a phagosome
- Fuses with lysosomes to form a phagolysosome
- Phagolysosome acidifies with H+ pumped in and superoxides kill bacteria; activates protease and stimulates the production of superoxides which kill bacteria
Exocytosis: the expulsion of the digested microbe
Pattern recognition receptors (PRR)
Bind complex molecules that are unique to microbes; fundamental in recognising the unique pathogen patterns on the surface of microbacteria; power switch which tells the adaptive immune response to then start making the wanted antibodies
Toll-like receptors (TLR)
Leucine Rich Repeat (LRR) that look like slinkies; the activation produces a very strong inflammatory response through an important inflammation pathway which drives everything else; without this, there is no effective immune response
Pathogen Associated Molecular Patterns (PAMPs)
Molecules unique to microbes recognised by PRRs; structurally very complex (e.g. lipopolysaccharides); evolutionarily stable (don’t change too much); stimulate the power switch for the adaptive response
LPS
Lipopolysaccharide; highly complex glycolipid molecule that stimulates TLR4 cross-linking to signal a powerful inflammatory response; it is a powerful pyrogen so tiny amounts of it in the blood can cause fever, rigours and hypotension, can be fatal if not controlled - known as septic shock and often a fatal consequence of an uncontrolled Gram-negative infection in the blood
Origin of adaptive immunity
The event occurred ~500 million years in jawless fish that allowed a region of the genome to rearrange; likely that an ancient transposon inserted itself into the DNA of a germ cell of the fish, within a primordial receptor gene and then the transposase moved to another part of the genome, could then rearrange bits of the genome within these recognition sequences attached
Recognition Sequences
RS; located at the ends of all the Ig and TcR gene segments
Transposons
Jumping genes found in primitive organisms; immunoglobulin (Ig) and T cell Receptor (TcR) gene regions or loci use the same mechanism; cut and shifted by the transposase enzyme
Transposase
The enzyme that cuts and shifts the transposon; the ancient transposase still present in our genome are called RAG1 and RAG2 (Recombination Activation Genes)
Adaptive immunity response
Recognition of traits specific to particular pathogens using a vast array of receptors (has memory); provided by lymphoid cells; has memory, the affinity of B cells towards antigen changes with both time and persistence of antigen; secondary response is more rapid than slow naïve response
Which organisms have adaptive immunity
vertebrates only
Adaptive immunity when born
A massive repertoire of B and T lymphocytes, each representing a different antigen specificity randomly produced by rearrangement of the genes coding for the antigen receptors
Immunisation primary response of B lymphocytes
First immunisation with antigen results in a rise in antigen-specific low-affinity IgM in the blood; peaking at about 2 weeks after but then diminishes rapidly
Immunisation secondary B cell response
Responses after the first immunisation (boosts; about a month apart) generates a rapid and intense burst of antigen-specific high-affinity IgG in the blood that lasts months or years
Best vaccines
Inactive variants of bacteria toxins that rapidly produce high affinity neutralising IgG that binds to the toxin before it binds to its target receptor
B cells
(B lymphocytes) begin in the bone marrow and mature in secondary lymphatic organs (spleen and lymph nodes); produce antibodies and form the humoral (soluble) arm of the adaptive response
B cell receptor
Antigen receptor; membrane-bound IgM molecule which is associated with intracellular molecules that transmit an activation signal via phosphorylation
T cell receptor
Antigen receptor (TcR); immunoglobulin-like molecule found on the surface of all T-lymphocytes; gene locus undergoes rearrangement but not affinity maturation; associated with a number of surface molecules - important ones being CD4 and CD8 (distinguish two functionally different types of T-lymphocytes)
Lymphatic system
Circulatory system for immune cells that connects hundreds of small lymph nodes (draining sites that interface with the environment - throat and gut); carries clear fluid (lymph) that drains tissues from the interstitial space between cells
Primary lymphoid organs
Bone marrow and thymus
Secondary lymphoid organs
Lymph nodes and spleen; filled with lymphocytes; where B cells form follicles that contain germinal centres where they encounter antigen and undergo affinity maturation
Immunoglobulin fold
The most basic element of the Ig molecule, smallest possible domain and the most common fold; consists of two anti-parallel beta-sheets made up of seven (Constant) or nine (Variable) beta-strands connected by loops (which form the antigen-binding site); sheets lie at a 30-degree twist to each other forming a very soluble beta-barrel structure; single di-sulphide bond stabilises the structure
Loops in Ig fold
Connect the strands of the molecule and form the antigen-binding site; not constrained in the structure so allow extreme amino acid diversity without compromising the overall stability
IgG antibody protein structure
Consists of 4 protein chains that are all made up of repeating Ig domains; 4-5 domains in heavy chains (50-75kD each; joined by disulphide bonds) and 2 domains in light chains (25kD; joined to the H chains by disulphide bonds); ‘Y’ shaped antibody has two flexible arms and the antigen-binding sites are located at the tip of the two arms (formed from the N terminus domains of the L and H chains); total MW is always a multiple of 25kD (150kD)
Hinge region in antibody molecule
Important feature; bound by disulphide bonds which allow the two arms of the ‘Y’ structure to flex
Binding sites antibody molecule
All identical because they all came from the same B cell; tips of the two domains are hypervariable (all amino acids sequences change between different molecules)
Effector antibody molecule
Bound by phagocyte Fc receptors and complement component C1; once antibody is bound to the surface of the bacteria, the structure of the antibody will change slightly and complement then binds in or phagocytes come to recognise it (initiates phagocytosis)
Classes of Ig molecules description
Humans have 5 classes, determined by the H chain gene used; IgM is the default antibody made by all immature B cells; when the B cell encounters antigen and activates,, it switches to use the gamma gene to produce an IgG molecule; rarest class is IgE which constitute a very small amount of total Ig in the blood (causes atopic allergy)
IgM
Default Ig made by all naïve B cells; comes in a membrane-bound (monomer; B-cell antigen receptor BCR) and soluble (pentamer; has 10 binding sites) form; reacts strongly to surfaces such as microbes through avidity binding; good at fixing complement with 5 Fc regions that bind complement component C; low affinity, high avidity molecules
5 Ig classes
IgM (default; Serum and membrane); IgG (Serum); IgD (Serum and membrane); IgE (Serum); IgA (Serum and mucosa); different functions depending on which H chain gene is used
Affinity
When the sum of the attractive molecular forces at two surfaces exceeds the repulsive forces, there is affinity; the higher the affinity, the fewer molecules it takes per unit volume to associate and dissociate slowly
Avidity
Results from multiple affinity contacts; like Velcro, the strength of binding can be orders of magnitude higher than the individual affinities; very important concept in immunology
Ig molecules which activate complement
IgG and IgM both bind with avidity; they expose the Fc region which allows complement to activate - which then activates its own molecules and MAC complex inserts into the bacterial membrane
Ig molecule which is secreted at mucosal sites
IgA found primarily in secretory sites (such as tears, saliva, breast milk); long-lasting in the gut and provides a very strong immunity to babies
Ig molecule involved in placental transfer
IgG only class that can transfer across the placenta; babies don’t have a developed B-cell response when they are born and so their innate immunity is very dependent on the antibodies received from their mother
Ig molecule with a high affinity receptor on mast cells
IgE very strongly associated with allergies; has the ability to bind to large molecules (like pollen grains); receptor on certain types of myeloid cell (mast cells; resident in mucosal sites) which binds very tightly to IgE; mast cells degranulate and release histamines
Ig molecules in a membrane-bound form
IgM and IgD
Complementarity
The measure of how well two molecules want to interact with each other; affinity arises and an antibody forms complementarity if the sum of the attractive forces exceeds the sum of the repulsive forces
Antigen binding site
Amino acid variation is found in 3 discrete regions called the CDRs - 3 loops that connect the strands in the first domains of the H and L chains
For Ig and TcR, they are formed from the 6 protein loop regions that connect the beta-strands in the Ig variable domain (first N terminal domain in H chains and L chains)
Complementarity determining regions
CDR; loop regions that make the antibody binding site; contain massive amino acid diversity through the rearrangement and imprecise joining of germline gene segments in the Ig and TcR locus
Antigen receptor repertoire
Gene possibilities can undergo somatic hypermutation; once arranged they can continue to change base paring through random mutations - some occur at the binding site and some of those will produce a result where the antigen affinity increases; this molecule (made by the B-cell) is selected and successive rounds of affinity maturation and selection occur
Segments of germline Ig and TcR gene loci
Variable, Diversity, Joining and Constant regions, each of which can be rearranged; the light chain has no D segments; within these regions, there are many segments
Recombination in the Ig locus
RAG1 and RAG2 are responsible for rearrangement and are only active in B and T lymphocytes; an immature B lymphocyte in the bone marrow first rearranges a heavy chain D segment to join to a J segment and then a V segment joins the D segment - forms a pre-RNA which is then spliced to a C region segment; joining is very imprecise and so base pairs are changed during repair - leads to huge variation at the VDJ join
VDJ join region
Codes for CDR3
Light chain rearrangement
It rearranges but there are no D segments so V joins to J; imprecise joining results in massive diversity in certain amino acids
Clonal selection
The immune system produces as many possible antigen receptor combinations through a type of gene rearrangement of the Ig locus; individual B cell cones are selected to mature when they encounter antigen within germinal centres in lymph nodes
Affinity maturation
Only occurs in B cells; when they encounter antigen in the lymph nodes, antigen triggers a small number of B cells with a low-affinity receptor to proliferate; somatic hypermutation occurs where random mutations are introduced into the V-D-J genes - some will increase the affinity; after successive rounds, the mature B cell has a high-affinity receptor - becomes a plasma cell (secretes high-affinity soluble IgG) or a memory cell (wait for next interaction in lymph nodes)
Vaccination
Affinity maturation is the fundamental mechanism behind this; driving a weak naïve B cell to undergo rearrangement and extensive hypermutation to eventually secrete a high-affinity IgG
Thymus
The gland which sits just above the heart and is largest at birth, reduces in size with age; immature lymphocytes from the bone marrow migrate here to mature
T lymphocyte maturation
Migrate from the bone marrow to the thymus and become T-cells; at this stage, they express both the CD4 and CD8 co-receptors (surface antigens); encounter MHC class 1 and 2 molecules - the process of education to learn what self looks like
CD4 cells
Helper T-cells which interact with macrophages expressing parts of bacteria on their surfaces and respond by secreting cytokines (proliferation of the T-cells); only respond to the MHC class 2 and express the CD4 antigen; 80% of blood T-cells; have 4 functional subsets;
Subsets of CD4 cells
Treg - suppresses/regulates the immune response
Th1 - promotes cell-mediated immunity (cellular response)
Th2 - promotes antibody-mediated immunity (B-cell response)
Th17 - promotes inflammation
CD8 cells
Killer/cytotoxic T-cells (CTL) which recognise the surfaces of infected cells (viral proteins broken down and presented on the cell surface) and kill them; done by introducing perforins and granzyme into the cell; T-cells which respond to the MHC class 1; only express the CD8 antigen; 20% of blood T-cells
MHC
Major Histocompatibility Complex; the genetic locus that regulates histocompatibility; encodes MHC molecules which actively present viral antigens to the T-cell receptor; highly polymorphic and important in bone or tissue transplant - the immune cells will recognise the tissue as foreign if the MHC molecules are not extremely similar
Viral immunity
Requires self: antigens encoded by MHC and non-self: antigens encoded by the virus; recognition of viral immunity is regulated by self component
MHC restriction
T-cells see two antigens at the same time: foreign peptide antigen (non-self) embedded in MHC and MHC molecules; first coined when n experiment in congenic mice showed that they only killed virally-infected cells from their own strain - meant that the CTL were restricted by MHC, explained how viral immunity depends on MHC to present antigens and why transplanted tissue is rejected
MHC restriction (molecule)
TcR is recognised on the MHC on the target cell; antigen binding surface of the TcR binds to the top of MHC which represent the “peptide groove” containing the foreign peptide antigen; the TcR has affinity towards the combination of MHC
HLA
Human Leukocyte Antigens; 6 different molecules expressed on human cells - a total of 12 antigens expressed on the cell surface due to the co-dominance (maternal and paternal); human version of MHC
MHC class 1
Picks up peptide antigens from inside the cell (intracellular) and presents them to CD8 cytotoxic T-cells - which can then effectively kill the presenting cell; polymorphic region (2 alpha-helices); between the groove is a viral peptide - synthesised inside the cell; beta-2-microglobulin (a molecule which holds the whole unit in the correct orientation)
MHC class 2
Picks up digested antigens from the phagolysosome (extracellular pathogens) and present them to CD4 helper T-cells; has alpha and beta chains; polymorphic groove allows the peptide to bind to it (longer because it comes from a different source; usually antigens are broken-up pieces of bacteria as a result of phagocytosis
HIV virus and AIDS
Uses the CD4 antigen as its receptor to enter and replicate in helper T-cells; AIDS is a condition resulting in a long-term depletion of the CD4 T-cell population; victim slowly loses the ability to respond to simple infections
MHC polymorphism
Amino acid sequences vary greatly across the population and there are hundreds of different variations at each MHC locus; transplantation is difficult because T-cells from the patient recognise the donor MHC antigens as foreign; they must take immunosuppressants
MHC class 1 molecules
HLA-A, B and C
MHC class 2 molecules
HLA-DR, DP and DQ
2 major consequences of MHC polymorphism
- Tissue transplantation is difficult except for identical twins
- MHC polymorphisms are strongly linked to many autoimmune diseases (due to it being the only polymorphic part of the entire genome)
Most common MHC disease associations
Addison’s disease (disease of the adrenal gland), Type 1 diabetes, rheumatoid arthritis, multiple sclerosis and ankylosing spondylitis; T-cells are reacting to self-antigens that are best presented by these MHC molecules
Major types of type 1 allergies
Asthma, allergic rhinitis (seasonal hay fever), skin eczema, urticaria (hives), insect allergies, animal dander, drugs, large food proteins, nickel, anaphylaxis
Allergy
The most common form of immune disorder; about 30% of people have some kind of it
Hay fever allergy
(seasonal rhinitis) common amongst Caucasians; many types of allergens limited to the mucosal sites of the eyes, nose, throat and upper respiratory tract
Skin allergy
Second most common site for an allergic response; urticaria or hives caused by the release of histamines into the tissue from mast cells in the skin; oedema (swelling) caused by leakage of fluid into the intercellular space
Asthma allergy
A type of immediate-type allergic response; bronchial tubes thicken and inflame in response to a range of allergens or other triggers (cold air)
Anaphylaxis
(or anaphylaxis shock) is a serious consequence of an allergy; oedema and swelling occurs at multiple anatomical sites that are distant from the original site of allergen challenge; most common sites lips, eyes and throat swell but can extend to airways and the gut; treatment is an immediate injection of epinephrine (adrenaline)
4 classifications of hypersensitivity
Type 1 (atopic allergy), type 2 (complement-mediated), type 3 (serum sickness), type 4 (delayed type)
Type 1 atopic allergy
Atopic allergy (IgE mediated, immediate response); the FcεR receptor on mast cells has a very high affinity toward IgE:antigen complexes; when IgE binds large complex antigens (like pollen) it triggers local mast cells to rupture and empty their granules (powerful inflammatory mediators) which cause an allergic reaction
Type 1 hypersensitivity
smooth muscle and blood vessels constrict, mucous glands secrete mucous, platelets are attracted to the site and cause platelet irrigation and clotting, sensory nerve ending stimulation occurs (which causes the pain); can be treated with antihistamines which impersonate histamines and lock the receptor to prevent the stimulation of downstream events
Type 2 hypersensitivity
Complement mediated (medium response); involved FcR, complement and neutrophils; antibody in newborn baby reacts to a protein on the BM of the RBC and induces a similar response by neutrophils, complement is deposited; neutrophils try to digest the membrane of the RBCs which results in the lysis of RBCs and haemolytic anaemia (rhesus); anti-RhD is an antibody that the mother has developed abnormally against the blood of the fetus during gestation
Rhesus baby
Acute haemolytic anaemia; rhesus is a simple carbohydrate that s expressed on the surface of RBCs which can generate an antibody response; this condition is caused by a blood group antigen RhD on the surface of RBCs; maternal antibodies developed to foetal RhD cause lysis of newborn RBCs
Treatment or allergy by desensitisation
Works in about 50% of patients; slowly drive B-cells to produce IgG instead of IgE - competition when they are challenged by the antigen; dependent on how well you can generate an IgG response and whether they will effectively compete for the IgE that is resident on the mast cells
Monoclonal antibodies
Single specific antibodies that are now used as powerful drugs to treat a range of conditions; a hybrid between B-cells and myeloma cells that still produces the same antibody that the B-cell produced
Monoclonal antibodies pros
Highly specific for the intended target so no “off-target” effects; can be tailor-made with just the right affinity; humanised so they stay in the bloodstream for months; no adverse reactions or toxicity to the antibody; can be modified to be “bi-specific” for even greater potency
Monoclonal antibodies cons
Expensive to develop and make commercially; side effects of their function can be serious
