SAQs Flashcards
1
Q
Why are post mortem examinations performed? (9)
A
- 1). Confirm or refute a clinical diagnosis:
- Was the diagnosis correct?
- Can you refine the differential diagnoses?
- Was there another concurrent disease?
- 2). Failure of treatment:
- Why did the treatment of a clinical diagnosis fail?
- Clinical audit - e.g. morbidity + mortality rounds (MM rounds).
- 3). Sudden death - to provide a diagnosis when there is no clinical diagnosis.
- 4). Herd, group or population health:
- Rapid diagnosis of disease.
- Additional opportunity to implement treatment, nutrition or management changes to prevent further losses of individuals or production.
- 5). Surveillance:
- Monitor endemic disease.
- Detect exotic/notifiable disease.
- Monitoring effects of husbandry/management changes.
- Public health.
- 6). Forensic - crime involving animals:
- Cause of death, disease/health status, degree of suffering, obtaining trace evidence.
- Insurance.
- Malpractice inquests.
- 7). Zoological collections - routine samples.
- 8). Obtaining samples - for further samples e.g. histopathology, microbiology, bacteriology, virology, mycology, parasitology, trace element analysis and toxicology.
- 9). Research:
- Toxicology pathology.
- Tissues for further study - pathology, clinical, basic science and retrospective studies.
2
Q
Descriptors used to describe lesions. (11)
A
- 1). Organ/tissue
- 2). Position - topography
- 3). Number
- 4). Weight
- 5). Distribution: random, symmetrical, focal, multifocal, multifocal to coalescing, miliary, segmental, diffuse.
- 6). Contour: raised, depressed, flat.
- 7). Size: measure in 3D, uniform size or non-uniform size.
- Size of organs - smaller/larger than normal, compare paired organs, dynamic organs (being remodelled) - rapidly, moderately, slowly.
- 8). Colour
- 9). Shape e.g. circular, spherical.
- 10). Consistency
- 11). Smell
3
Q
Compare and contrast cytology and histopathology (14)
A
4
Q
Differences between innate and adaptive immunity (7)
A
Innate - first line of defence.
- Humoral and cell-mediated.
- Fast, non-specific.
Adaptive - T-cells and B-cells, highly controlled + more specific.
- Humoral - B-cells produced antibodies.
- Cell-mediated - T-helper cells produced cytokines.
- Slower to develop (5-6+ days).
- Based on clonal selection of antigen-specific cells.
- Primarily mediated by memory, not naive lymphocytes.
5
Q
How do cells get where they are required? (4)
A
- 1). Cytokines (TNF / IL-1) produced by macrophages cause dilation of local small blood vessels.
- 2). Leucocytes move to periphery of blood vessel as a result of increased expression of adhesion molecules (selections, ligands for integrins and chemokines) by endothelium
- Chemokines displayed on endothelial surface and bind to receptors on the rolling leucocytes, resulting in activation of leucocyte integrins to a high-affinity binding state.
- Activated integrins bind to their Ig super family ligands on endothelial cells, mediating firm adhesion of leucocytes.
- Leucocytes crawl to junctions between endothelial cells and migrate through venular wall.
- 3). Leucocytes extravasate out the blood at the site of infection (flow out) at site of infection.
- 4). Blood clotting occurs in microvessels.
6
Q
Phagocytosis (5)
A
- Recognition (using opsonins) and attachment of particle by leucocyte.
- 1). Bacterium becomes attached to the membrane evaginations (pseudopodia).
- 2). Bacterium is ingested, forming phagosome.
- Prior to activation, anti-microbial peptides and enzymes are stored in granules as lysosomes.
- 3). Phagosomes fuses with lysosome —> phagolysosome.
- Phagosomes fuse with primary and secondary granules. Rac2 (G protein) induces assembly of a functional NADPH oxidase in the phagolysosomes membrane, leading to generation of O2^- (destroy bacteria using free radicals).
- Acidification as a result of ion influx released granule proteases from granule matrix.
- 4). Bacterium is killed and then digested by lysosomal enzymes.
- 5). Digestion products are released from cell.
7
Q
Antimicrobial mechanisms of phagocytes (6)
A
8
Q
The complement system activation pathways (3)
A
- 1). Classical - antigen-antibody immune complexes - IgM or IgG binds to multivalent antigen.
- Allows binding of C1q, beginning process of complement deposition.
- 2). Lectin - PAMP recognition by lectins.
- Lectins bound to microbial surfaces serve as docking sites for MBL-associated serine proteases (MASPs).
- MASPs cleave C4 and C2 to form the C3 convertase.
- 3). Alternative - spontaneous hydrolysis or pathogenic surfaces. Initiated in three ways:
- Alternative tickover pathway - when C3 accumulates - usually continuously produced.
- Alternative properdin-activated pathway - properdin should stabilise and activate alternative pathway, binds to microbes and makes properdin (pathogen recognition receptor for Neisseria bacteria (colonies mucosal surfaces).
- Alternative protease-activated pathway.
- Alternative complement activation can occur as a consequence of blood clotting - thrombin and plasmin can cleave C3 + C5 which released toxins C2A and C5A.
9
Q
Effect of cytokines (innate immunity) (5)
A
10
Q
Innate lymphocytes - NK cells mechanism (4)
A
11
Q
Inflammatory response (innate immunity) (4)
A
12
Q
Dendritic cell function (summary) (4)
A
13
Q
MHC class II - antigen processing and presentation pathway (5)
A
14
Q
MHC class II - antigen processing and presentation pathway (5)
A
15
Q
Cytokine of IL-1 family - pro-inflammatory response (6)
A
- IL-1α and IL-1β bind to IL-1RI/L-1RAcP - has inhibiting ligand/receptor pair to shut down function.
- IL-18 - e.g. of redundancy, also processed in secreting cells, expressed by macrophages and DCs in early responses, inhibition through binding of cytokine before it binds to signalling receptor.
- IL-33- constitutively expressed in smooth muscle and bronchial epithelial, induces Th2 cytokines that promote T-cell interactions with B cells, mast cells and eosinophils. Receptor is also a heterodimer with IL-1RAcP.
16
Q
Haematopoietin (Class I) family cytokines (4)
A
•Gamma-chain IL-2R = protoype.
Beta-chain bearing subfamily - includes receptors for IL-3, IL-5 and GM-CSF.
- Exhibit redundancy - activate granulocytes (eosinophils/basophils); stimulate blood-cell differentiation; activate monocytes.
- Gp130 receptor subfamily - includes IL-6 and IL-12 receptors, signalling pathways induced are similar to those induced by interferons.
17
Q
Class II (Interferon) cytokine family (3)
A
- 1). Type I interferons -secreted by activated macrophages and dendritic cells.
- Interferons alpha = a family of about 20 related proteins.
- Interferon beta = regarded as a primary modulator + potent antiviral effects limited by more restricted receptor expressions.
- 2). Type II interferon (interferon-gamma) - dimer produced by activated T/NK cells.
- Potent modulator of adaptive immunity.
- 3). Type III interferon family.
18
Q
Interferon (Class II) cytokine family signalling and inhibition pathway (6)
A
19
Q
TNF cytokines (3)
A
- Regulates many activities - development, effector function, and homeostasis of cells of the skeletal, neuronal, and immune systems.
- May be soluble (form trimers, type 2) or membrane-bound.
- TNF receptors - presence of cysteine-rich domains (CRDs), most type I membrane proteins.
20
Q
TNF receptors signalling - Fas receptor (5)
A
21
Q
IL-17 family cytokines (7)
A
22
Q
Chemokines directing leucocyte migration - signalling (8)
A
23
Q
Adaptive immunity - signal transduction in B cells (5)
A
24
Q
Adaptive immunity - T-cell receptors and signalling (5)
A
25
Mechanism of V(D)J recombination (3)
* Generating large diversity of antigen-specific receptors.
* Mechanism of somatic recombination that occurs only in developing lymphocytes during the early stages of T and B cell maturation. It results in the highly diverse repertoire of antibodies/immunoglobulins and T cell receptors (TCRs) found in B cells and T cells, respectively.
26
Mechanisms that generate antibody diversity in naive B cells (4)
* 1). Multiple gene segments.
* 2). Nucleotides inserted between joints.
* 3). Exonuclease trimming at junctions.
* 4). Combinatorial diversity, heavy chain pairs light chains.
27
Early thymocyte development (4)
* Thymocytes can either express either alpha-beta TCR or gamma-delta TCR - never both.
* DN thymocytes destined to express conventional alpha-beta TCR undergo beta-selection - beta chain is paired with a pre-T-alpha chain to form a pre-TCR complex (with CD3 proteins).
* If functional pairing ---\> rearrangement of T cell receptor alpha chain + prevents further beta-chain rearrangement = allelic exclusion ---\> expanded double-positive (DP) thymocytes (CD4 and CD8), stimulates proliferation.
* Positive selection - selects thymocytes bearing receptors capable of binding self-MHC molecules, resulting in MHC restriction.
* Negative selection - selects against thymocytes bearing high-affinity receptors for self-MHC/peptide complexes, resulting in self-tolerance.
**Summary:** BM ---\> thymus (thymocytes) ---\> DN (double negative, CD4^+ and CD8^+ not expressed) ---\> beta-selection ---\> DP = express CD4^+ and CD8^+ ---\> +ive and -ie selection ---\> SP (CD4^+ or CD8^+ expressed) ---\> -ive selection removes autoreactive cells ---\> non-self committed T-cells released from thymus into bloodstream.
28
Innate immunity - B-cell development (3)
29
Innate immunity - compare and contrast B- and T- cell development
30
Summary of lymphocyte activation, differentiation, memory and effector responses (5)
* 1). Antigen recognition - 2^y lymphoid organs, following presentation of processed peptide antigen by MHC I or MHC II molecules on surface of mature professional APC.
* 2). Activation of antigen on specific cell.
* 3). Clonal expansion - driven by autocrine/paracrine action of IL-2 (major T-cell GF, binds to IL-2 receptor on the surface of activated T-cell).
* 4). Engagement of cytokines drives differentiation of activated T-cells to influence effector functions of cell.
* 5). Effector functions - memory/effector cells - migrate to infected tissues ---\> activation of macrophages, B-cells and other cells or killing of infected "target cells"; macrophage activation.
* Effector cells die by apoptosis and memory cells remain.
31
T-cell activation and signal hypothesis (3)
* Signal 1 - antigen-specific TCR engagement with MHC on APC
* Signal 2 - contact with co-stimulatory ligands on APC surface, needed for optimal T-cell activation and proliferation.
* Clonal energy results if a co-stimulatory signal is absent (peripheral mechanism body protects itself against autoreactive T-cells not removed in the thymus)
* Signal 3 - distinct polarising cytokines directing T-cell differentiation into distinct effector cell types from APC/other cellular sources
* All three combine to deliver necessary activation signals driving gene expression ---\> activation, proliferation + differentiation
32
T-dependent B cell responses
33
B cell responses maturation in germinal centres (2)
34
Antibody-mediated effector functions (4)
* 1). Virus and toxin neutralisation ---\> prevents pathogen-host binding.
* 2). Opsonisation ---\> phagocytosis.
* 3). Complement fixation and formation of membrane attack complex ---\> phagocytosis/lysis.
* 4). Antibody-dependent cell-mediated cytotoxicity (ADCC) ---\> NK-induced apoptosis.
35
Five major classes of antibodies (5)
* 1). IgM - first Ab produced in primary response (surface bound IgM is naive BCR).
* Complement fixation leading to MAC formation and target lysis.
* Formation of dense Ab-pathogen complexes that are efficiently engulfed by macrophages.
* 2). IgG - all variants bind Fc receptors, enhancing phagocytosis by macrophages.
* 3). IgA - isotype found in secretions, doesn't fix complement = no inflammation.
* Effective at neutralising toxins and pathogens.
* 4). IgE - allergy and asthma + protecting against parasitic helminths and protozoa.
* Degranulation of eosinophils/basophils.
* Release of molecules (pro-inflammatory e.g. histamine to damage large pathogens.
* 5). IgD.
36
Fc receptors (5)
* 1). Fc-gamma-Rs - bind to IgG, most diverse group, main mediators of Ab functions, most are activating receptors (three activating, one inhibiting).
* Will induce phagocytosis if expressed by macrophages - antibody-dependent phagocytosis (ADP).
* Will induce degranulation if expressed by natural killer cells – antibody-dependent cellular cytotoxicity (ADCC).
* 2). Fc-alpha-R - binds to IgA, expressed by myeloid cells.
* Contributes to pathogen destruction by triggering ADCC and phagocytosis.
* Stimulates myeloid cells to release inflammatory cytokines and generate superoxide free radicals to help kill internalized pathogen.
* 3). FcεR - expressed by granulocytes, low and high affinity type.
* Triggers a signalling cascade that releases histamines, proteases, and other inflammatory mediators.
* Most often associated with allergy symptoms.
* 4). pIgR - polymeric immunoglobulin receptor, expressed by epithelial cells.
* Initiates transport of IgA and IgM from blood to lumen of tissues.
* Responsible for carrying Ab into tears and milk, and populating gut mucosa with IgA Ab to protect against ingested microbes and toxins.
* 5). FcRn - neonatal Fc receptor, related to MHC class I, expressed on epithelial/endothelial cells.
* Helps to carry Ab ingested in milk across epithelial cells of the intestine into the bloodstream.
* Can augment the role of pIgR to better carry IgG into milk and GI/respiratory secretions.
* In adults, can help recycle IgG taken up through endothelial cell pinocytosis processes back into blood.
37
CD8^+ CTLs recognise and kill infected/tumour cells via TCR activation (5)
38
How CD8^+ CTLs kill cells meachanism (2)
39
Acute inflammation summary - reactions of vessels (5)
**Blood vessels:**
* 1). Few seconds of vasoconstriction - to delay and allow bleeding to stop.
* 2). Vasodilation.
* 3). Increased vascular permeability (vessels leakier) - allows escape of exudate into tissue (oedema).
* Contraction of endothelial cells (increasing interendothelial spaces), due to stimuli e.g. bacteria.
* Endothelial injury (necrosis and detachment).
* Increased transport through endothelial cells.
* Fibrin - stops stimulus spreading to nearby tissue, assists clotting, allows leucocytes to target inciting cause of inflammation, acts as scaffold for endothelial migration.
* 4). Stasis = vascular congestion: allows time for leucocytes to accumulate on vascular endothelium.
* Fluid loss + inc vessel diameter ---\> slower blood flow (dec pressure, dec velocity).
* Increased concentration of RBCs ---\> increased viscosity of blood.
**Lymphatic vessels** - lymph flow is increased in inflammation, draining oedema fluid to leucocytes and cell debris also enter the lymph.
•Proliferation of lymphatic and blood vessels + LNs (hyperplasia of lymphoid follicles) in inflammation + secondary inflammation.
40
Acute inflammation - increased vascular permeability (4)
* 1). Contraction of endothelial cells
* Increased spaces between endothelial cells - for neutrophils and proteins to leave.
* Immediate + transient response (short period of time).
* 2). Endothelial injury - direct damage to endothelial cells leading to necrosis and detachment from the basement membrane.
* Sever injuries e.g. burns / actions of microbes that target endothelial cells.
* Neutrophils can damage endothelial cells whilst they are adhered during inflammation.
* 3). Transcytosis - fluids and proteins transported through endothelial cells.
* Channels created by vesicles and vacuoles near intercellular junctions to allow transport. Mediators e.g. VEGF, increased no. + size of channels.
* 4). Fibrin - fibrinogen polymerises to form fibrin which:
* Stops stimulus spreading into nearby tissue.
* Allows leucocytes to target the inciting cause of inflammation.
* Assists in blood clotting.
* Acts as a scaffold for endothelial migration during wound healing.
41
Acute inflammation summary - reaction of leucocytes (3)
**Recruitment of leucocytes:**
* 1). Adhesion to the endothelium - due to stasis, blood flow slows.
* Leucotyes make contact with the endothelium (margination) and start rolling before coming to a rest and adhering with the endothelium by complementary adhesion molecules (enhanced by cytokines).
* Selectins - L-selectin (leucoand P-selectin (endothelium) - mediate the rolling.
* Intergrins on endothelial cells - slow down the leucocytes further and allow stronger adhesions to form (ICAM-1, binds to beta-2 integrins, on neutrophils, and VCAM-1, binds to beta-1 integrins, on eosinophils) to stop the rolling, reorganise cytoskeleton so leucocytes spread out on the endothelial surface.
* 2). Migration across the vessel wall - mediated by PECAM-1.
* 3). Migration to the stimulus (once out of circulation) - chemotaxis, chemotactic agents bind to receptors on surface of leucocytes (GPCR, TLRs, cytokine receptors:
* Opsonin receptors - proteins used to coat organisms for phagocytosis e.g. antibodies, proteins and lectins.)
42
Acute inflammation - cell-derived mediators (7)
* 1). Vasoactive amines - first mediators at scene, pre-packaged in cells.
* Histamine - in mast cell granules (+ basophils and platelets), binds to H1 (histamine) receptors on microvascular endothelial cells, causes dilation of arterioles and increases permeability of venules.
* Serotonin (also dilates vessels like histamine) - in platelets, certain neuroendocrine cells + mast cells, stimulated when platelets aggregate, link between clotting and inflammation.
* 2). Arachidonic acids are degraded by enzymes to form metabolites (prostaglandins, leukotrienes and lipoxins) with effects such as:
* Vasodilation / inhibition of platelet aggregation / vasoconstriction / platelat aggregation / vasodilation / inhibit neutrophil adhesion / bronchospasm / increased vascular permeability
* 3). Platelet-activating factor (phospholipid-derived mediator) - from inflammatory cells and cause:
* Platelet aggregation, vasoconstriction, bronchoconstriction; extremely low conc = vasodilation, increased venular permeability.
* Inc leucocyte adhesion to endothelium, chemotaxis, degranulation and oxidative burst.
* Inc synthesis of other mediators by leucocytes and other cells.
* 4). Oxygen-derived free radicals (reactive oxygen species (ROS)) - production dependent on activation of NADPH oxidase, stimulate inflammation as they cause more damage.
* Amplify inflammatory response - inc expression of chemokines, cytokines and endothelial leucocyte adhesion molecules.
* ROS in leucocytes destroy phagocytosed microbes so their release can cause host damage: endothelial cell damage, with resultant inc vascular permeability, injury to other cells, inactivation of antiproteases, leads to unopposed protease activity w/ increased destruction of ECM.
* 5). Nitric oxide - produced by endothelial cells and macrophages, relaxes smooth muscle ---\> dilation.
* 6). Cytokines and chemokines (substances released from damaged/dying cells):
* Cytokines e.g. TNF and IL1 - local effects inflammatory = inc expression of leucocyte adhesion molecules, inc procoagulant activity, activation of leucocytes, production of further cytokines, and repair = proliferation of fibroblasts, inc collagen synthesis; systemic effects = fever, leucocytosis, inc APPs, dec appetite, lethargy.
* Chemokines - chemoattractant for different leucocytes.
* 7). Neuropeptides - secreted by sensory nerves and leucocytes, include substance P and neurokinin A.
* Substance P - transmission of pain signals (lowers pain threshold, feel pain), regulation of blood pressure (ANS), stimulation of section of endocrine cells, inc vascular permeability.
43
Acute inflammation - cell-derived mediators, arachidonic acid (AA) metabolites + pharmacology (3)
* Cell membrane phospholipids - phospholipase (inhibited by steroids, no metabolites made) - Ca^2+ can activate, it digests a bit of the membrane to make arachidonic acid (key 'ingredient' of pro-inflammatory material).
* 1). Cyclooxygenase (COX-1 and COX-2 inhibited by NSAIDs e,g, aspirin) - degrades arachidonic acid into prostaglandin G2 (PGG2) which then degrades into a number of others, different prostaglandins have different effects, some may be anti-inflammatory:
* In-built anti-inflammatory system - calms down inflammation.
* Prostacyclin (PGl2) - vasodilation, inhibits platelet aggregation.
* Thromboxane A2 (TXA2) - vasoconstriction, promotes platelet aggregation. (Antagonistic)
* 2). Lipoxygenase - acts on arachidonic acid to make:
* Lipoxins inhibit neutrophil adhesion and chemotaxis.
* Leukotrienes (blocked by montelukast drug) - vasoconstriction, bronchospasm, increased vascular permeability (effects of asthma).
* Shoudn't give asthmatics NSAIDs/COX inhibitors as it removes one of the substrates which could lead to the increase in production of leukotrienes as they become more favoured, results in bronchospasm.
44
Acute inflammation - plasma-derived mediators (2)
* 1). Complement system - mechanism of killing bacteria - makes it go inside out
* Formation of membrane attack ---\> lysis of microbe.
* Recognition of bound C3b by phagocytes C3b receptor (like opsonin) ---\> phagocytosis.
* Inflammation - recruitment of leucocytes, leading to destruction
* 2). Kinins - another interaction w/ clotting system
* Vasoactive peptides
* Bradykinin
45
Termination of acute inflammation (2)
* 1). Half-life of mediators is short + they are rapidly degraded (apoptosis) once released e.g. neutrophils.
* 2). Switch from pro- to anti-inflammatory mediators:
* Lipoxins.
* Macrophages produce anti-inflammatory cytokines e.g. TFG-beta and IL-10.
* Resolvins and protecting (PUFAs) = antagonistic effects.
* Neural inhibition (cholinergic discharge) that inhibit TNF production.
46
Acute inflammation - morphological appearance
* 1). Serous inflammation
* 2). Catarrhal inflammation
* 3). Fibrinous inflammation
* 4). Suppurative inflammation
* 5). Abscess
