Key Terminology & Definitions - Pathology Flashcards
Aetiology
Cause of disease
Pathogenesis
Mechanisms (progression from initial stimulus to disease expression) that lead to diseased state in response of cells and tissues to aetiologic agent.
Gross pathology
Recognition and description of macroscopic, morphological changes to tissues and organs in the live or dead animal at biopsy, surgical removal or PM examination.
Antemortem
Before death
Post mortem
After death
The examination of a body after death =
PM examination / necropsy / autopsy
Yellow
Icterus
Pallor
Loss of blood/anaemia
Red-purple
Congestion, sepsis, bruising
Haemorrhage
Green
Bile imbibition, pseudomelanosis (green-black) (bacteria making sulfur compounds (H2S) = smell), some fungi
Gelatinous
Oedema, serous atrophy of fat
Pluck
Trachea, tongue, larynx, thyroids and parathyroids, oesophagus, heart and lungs.
Agonal
Changes that occur at or around time of death
Algor mortis
Cooling of the body after death
Rigor mortis
Contraction of muscles after death (due to lack of ATP, no re-cock of myosin head).
Autolysis
Breakdown of tissue as result of enzymes contained within cells = self-digestion
Putrefaction
Breakdown of tissues by bacteria
Desiccation
Loss of H2O from tissues exposed to the air after death
Livor mortis
Pooling of blood in dependent sites due to gravity
White / grey / yellow
Lack of blood, necrosis, icterus, fibrosis
Black
Melanin (melanosis, flat, melanoma, raised)
Gas (consistency)
Trapped in tissue = emphysema or autolysis
Fluid (consistency)
Looks or feels wet = oedema, blood, transudates, fluid
Soft (consistency)
Fluid rich, cell/stroma poor
Firm (consistency)
Fluid poor, cell/stroma rich
Hard/gritty (consistency)
Mineralised stroma/matrix, cartilage, bone, calcified tissue
Innate immunity
Pre-existing frontline defence that is always there; normal immune system animals are born with (non-specific)
Pathogen-associated molecular patterns (PAMPs)
Molecules with conserved motifs that are associated with pathogen infection that serve as ligands for host pattern recognition molecules such as Toll-like receptors (innate immunity)
Pattern recognition receptors (PRRs)
Recognise PAMPs and target them for clearance
Macrophage
APC - phagocytosis and activation of bactericidal mechanisms
Adaptive immunity) - stimulate already primed effector and memory T-cells (B cells as well
Dendritic cell
APC - antigen uptake in peripheral sites, specialised in activation of naive T-cells
Neutrophil
Phagocytosis and activation of bactericidal mechanisms
Eosinophil
Killing of antibody-coated proteins
Basophil
Promotion of allergic responses and augmentation of antiparasitic immunity
Mast cell
Release of granules containing histamine and active agents
Selectins
Bind carbohydrates and initiate leucocyte-endothelial interaction
Integrins
Bind to cell-adhesion molecules = an extracellular matrix, strong adhesion
Immunoglobulin superfamily
Various roles in cell adhesion, ligand for integrins
Phagocytosis
Engulfment and internalisation of materials such as microbes for their clearance and destruction
The complement system
A group of serum proteins circulating in inactive form, once activated —> target cell membrane lysis, chemotaxis, opsonisation to enhance phagocytosis
Opsonisation
Bacteria are altered by opsonins so as to become more readily and more efficiently engulfed by phagocytes
Enhancement of macrophages and phagocytosis
TLRs
Toll-like receptors (PRR) - innate immunity
CLRs
C-type lectin receptors (PRR) - recognise cell wall components - sugars/polysaccharides of bacteria/fungi
RLRs
Rig-i-like receptors (PRR) - RNA helicases, recognise viral RNAs
NLRs
Nod-like receptors (PRR) - sense bacterial products in products
Epitope
Part of an antigen molecule to which an antibody attaches itself
cDC
Conventional dendritic cells - professional APC, constitute expression of co-stimulatory molecules and stimulate naive T cells
MHC
Major histocompatibility complex that presents antigen to T-cells (MHC I = CD8^+, MHC II = CD4^+)
MHC I
Co-expressed but not covalently linked - CD8^+ (cytotoxic T helper cells = co-receptor)
MHC II
Heterodimer of alpha and beta chain - CD4^+ (T helper cells = co-receptor)
Cytokines
Proteins that mediate the effector functions of the immune system, they have endocrine, paracrine and autocrine actions
Enhance the expression of adhesion molecules in acute inflammation
E.g. TNF and IL-1
Chemokines
Chemoattractants for different leucocytes
Large family of small, secreted proteins that signal through cell surface G protein-coupled heptahelical chemokine receptors
Stimulate the migration of cells, most notably white blood cells (leukocytes)
Large family of cytokines
Many act on granulocytes
Granulocyte
Type of white blood cell that has small granules, containing proteins,
E.g. Neutrophils, eosinophils, and basophils
CD
Cluster of differentiation molecule
Pleiotropy (cytokines)
One cytokine produces multiple effects
Redundancy (cytokines)
More than one cytokine induces the same effect
Synergy (cytokines)
Two (or more) cytokines work together to induce an effect
Antagonism (cytokines)
One cytokine can inactivate the effect of another
IL-1 family (cytokines)
Promote inflammation (most are proinflammatory)
Interferons (INFs)
A group of signalling proteins made and released by host cells in response to the presence of several viruses
TNF
Tumour necrosis factor - cytokine that regulates development, effector function and homeostasis of cells of the skeletal, neuronal and immune systems
Adaptive immune responses
Humoral and cell-mediated responses using B and T lymphocytes, slower to develop and more specific
Antigen
Processed peptide derived from a foreign or altered-self protein and presented by MHC class I (e.g. cytotoxic CD8 t cell) or II (e.g. helper CD4 t cell) May be protein, lipid, carbohydrate, nucleic acid - soluble, particulate, simple or complex
BCR
Membrane-bound immunoglobulin
Antibody
Secreted immunoglobulin
CH regions
Encode for different isotypes (functional classes) of antibodies
Thymocyte
Very early T cell lymphocyte in the thymus
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
TREG cells
Regulatory T-cells - negatively regulate immune responses - deplete local area of stimulating cytokines, produce inhibiting cytokines, inhibit APC activity, directly kill T cells
TREG cell - effector cytokine and effector functions
IL-10, TGR-beta (transforming growth factor) - regulation, suppression of immune and inflammatory responses
TH17 cell - effector cytokine and effector functions
IL-17A, IL-17F, IL-22 - inflammation
TH2 cell - effector cytokine and effector functions
IL-4, IL-5, IL-13 - allergic and anti-helminth responses
TFH cell - effector cytokine and effector functions
IL-4, IL-21 - B cell help in germinal centres
TH1 cell - effector cytokine and effector functions
IFN-gamma, TNF - cell-mediated immunity, macrophage activation, inflammation
TCM cells
Central memory T cells - live longer/divide more, can differentiate into several subsets depending on cytokine environment, IN 2^y lymphoid tissues
TEM cells
Effector memory cells - first-line defences, rapidly re-acquire effector functions on second Ag exposure, in tertiary tissues e.g. LNs
Avidity
Overall strength between the antibody and antigen
MAC
Membrane attack complex - complex of proteins typically formed on the surface of pathogen cell membranes as a result of the activation of the host’s complement system, and as such is an effector of the immune system
FC receptor
Antibody receptor involved in antigen recognition
IgM Ab
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.
IgG Ab
All variants bind Fc receptors, enhancing phagocytosis by macrophages, most abundant
IgA Ab
Isotype found in secretions, doesn’t fix complement = no inflammation.
Effective at neutralising toxins and pathogens.
IgE Ab
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.
Oedema
Release of excess fluid into tissues or body cavities
Exudation
Release fluids from the circulation
Exudate
Extracellular fluid (oedema) rich in protein and cells, has high specific gravity (thick, heavy, goopy)
Pus
Purulent exudate - rich in leucocytes (mainly neutrophils), debris of dead cells and maybe microbes = inflammation (maybe infection)
Transudate
Low protein content and little or no cellular material, low specific gravity e.g. heart, liver + kidney disease
Erythema
Heat redness
Endotheliotropic
Agent that directly targets endothelium
Transcytosis
Transportation of fluids and proteins through endothelial cells
VEGF
Vascular endothelial growth factor - mediator for transcytosis
Stasis
Vascular congestion
Lymphangitis
Secondary inflammation of lymphatic vessels e.g. bug bites going up arm
Adeno
Gland
Lymphadenitis
Inflammation of draining lymph nodes
Reactive/inflammatory lymphadenitis
Increase in size of lymph nodes due to hyperplasia of lymphoid follicles
Margination
When blood flow slows and stasis occurs, due to inflammation, the leucocytes start to make contact with the endothelial surface
Selectins
Proteins which mediate rolling (three types), bind to ligands in response to cytokines
Cytokines
Secreted by cells as part of the inflammatory response, enhance the expression of adhesion molecules
L-selectin
Expressed on leucocytes, complementary to E-selectins
E-selectin
Expressed on endothelial cells
P-selectin
Expressed on platelets and endothelial cells (clotting)
Integrins
Mediate the further rolling and slowing down of leucocytes to allow stronger adhesions to form; two types, beta-1 and beta-2
ICAM-1
Leukocyte-associated transmembrane protein on endothelial cells, binds to beta-2 integrins on neutrophils, monocytes and lymphocytes
VCAM-1
Leukocyte-associated transmembrane protein on endothelial cells, binds to beta-1 integrins on eosinophils, monocytes and lymphocytes
Diapedesis/transmigration
Movement of leucocytes through endothelium, down a chemokine concentration gradient
PECAM-1
Platelet endothelial cell adhesion molecule - mediates migration of leucocytes across vessel wall
Leucocyte adhesion deficiencies
Characterised by recurrent bacterial infections due to inability of leucocytes to adhere and reach site of inflammation
Chemotaxis
Migration of cells along a chemical gradient
Exogenous chemotactic agents
Bacterial products e.g. lipids, peptides
Endogenous chemotactic agents
Released by cells e.g. cytokines, complement system, arachidonic acid metabolites
G protein-coupled receptors
Found mostly on leucocytes, recognise short bacterial peptides containing N-formylmethionyl residues
Toll-like receptors (TLRs)
Recognise components of different types of microbes e.g. bacterial lipopolysaccharide
Cytokine receptors
Leucocytes express receptors for cytokines that are produced in response to microbes
Opsonin receptors
Proteins used to coat organisms of particles for phagocytosis e.g. antibodies, complement proteins and lectins (binds to CHOs)
Histamine
In mast cell granules, cell-derived mediator of inflammation, binds to H1 receptor on microvascular endothelial cells to cause dilation of arterioles and increased permeability of venules
Serotonin
In platelets, certain endocrine cells + mast cells in some species, cell-derived mediator of inflammation, platelet released a reaction - causes dilation of arterioles and increases permeability of venules
Heterophagy
Cell eating another cell
Thrombosis
Abnormal clotting of blood
Arachidonic acid
Oxidised to form pro-inflammatory (+ anti-inflammatory) material / degraded by cyclooygenase to form prostaglandins or 5-lipoxygenase to form leukotrienes and lipoxins
Leukotrienes
Increased vascular permeability, vasoconstriction and bronchospasm (effects of asthma)
Lipoxins
Inhibit neutrophil adhesion and chemotaxis
NSAIDs
Non-steroidal anti-inflammatory drugs, inhibits COX-1 and COX-2
COX-1/COX-2
Cyclooxygenase-1/2
Platelet-activating factor
Phospholipid-derived mediator - from platelets, basophils, mast cells, neutrophils, macrophages and endothelial cells
Neuropeptides
Secreted by sensory nerves and leucocytes, includes substance P and neurokinin A
Plasma protein derived mediators
Group of plasma proteins triggered by antibody fixation or microbial antigens, cause inflammation, phagocytosis and cell lysis
Catar
Mucous + serous inflammation (inc fluid + neutrophils), in gut
Abscess
Junction between acute and chronic inflammation, when pus not cleared up, exudate is firm, doesn’t have enzyme in neutrophils to continue pus production
Gamma-delta-T cell
Functions like cells of immune system (+ NK T-cell)
B-cell specific receptor
Detects antigen in naive, natural state
T-cell specific receptor
Antigen is processed and presented by MHC I/II
Immunoglobulin-alpha/beta (innate immunity)
Complex formed by B-cell with other transmembrane proteins (B-cell has very short cytoplasmic tail means itself cannot transmit signals upon engagement with antigen), have signalling motifs in their cytoplasmic chains
ITAM
Immunoreceptor tyrosine kinase activatory motif, signalling motif in which its phosphorylation triggers signalling cascades leading to transcription of B-cells + their activation
V(D)J recombination
The 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.
DN
Double negative thymocytes - don’t express CD4 or CD8, undergo beta selection, involving combination of T-cell receptor gene segments, those that survive express both CD4 and CD8 = double-positive
DP
Double positive thymocytes - undergo positive and negative selection to become a single positive (SP), only express CD4 or CD8
Negative selection screen removes autoreactive cells
Antigen presenting cell
DC, macrophage and B-cells - increase expression of MHC II CD80 and CD86
Fc receptors (adaptive immunity)
Fragment crystallisable region (Fc region) is the tail region of an antibody that interacts with cell surface receptors called Fc receptors and some proteins of the complement system. This property allows antibodies to activate the immune system.
Hypertrophy
Cells too big
Hyperplasia
Too many cells
Dysplasia
Disorganised arrangement of cells and abnormal pattern of tissue growth
Poorly differentiated cells
Metaplasia
Abnormal differentiation - change from one cell type to another
Cyst
Distended space +/- content
Atrophy
Cells too small
Pyogranulomatous inflammation
Neutrophilic + granulomatous inflammation
Coagulative necrosis
Tissue structure preserved, neutrophils
Caseous necrosis
Loss of architecture, usually associated with granulomas, macrophages
Liquefactive necrosis
Loss of structure, usually hard to capture on histology, neutrophils
Haemorrhage
Erythrocytes outside blood vessels
Thrombosis
Abnormal fibrin clotting inside vessels
Congestion/hyperaemia
Too many erythrocytes inside blood vessels (alveolar septa)
Thromboembolus
Abnormal material in blood vessel e.g. cartilage, bone, contrast medium, brain etc
Hypersensitivity
Excessive reaction to antigens
Autoimmunity
Immune system reacts to self-antigens
Immunodeficiency
Immune system fails to respond when it should
Amyloidosis
Creation of abnormal proteins that impair tissue function
Atopy
Localised reactions, often progress from acute perivascular inflammation to chronic inflammation/type IV hypersensitivity
Anergy
Inactivation of lymphocytes that antigen - no co-stimulatory signal, negative signal received
Suppression (peripheral tolerance)
Mediated by T regulatory cells - produce IL-4, IL-10, TGF-beta to inhibit lymphocyte activation
SLE
Systemic lupus erythematosus - prototypical autoimmune disorder, autoantibodies to range of cell components
Predominant antibody
Antinuclear antibody (AA) - form immune complexes (like type III hypersensitivity) and deposit in glomeruli, blood vessels, skin, joints
SCID
Severe combined immunodeficiency disorder - defects in humoral and cell-mediated immunity (T and B cells)
Often manifests as viral or fungal infections
Sever lymphoid hypoplasia
Amyloid
Pathologic protein formed of beta-pleated sheets of non-branching fibrils
Primary amyloidosis
Immune cell dysfunction, usually AL type, most common immune cell dysfunction that produces this is plasma cell tumour
Secondary amyloidosis
(Also known as reactive systemic amyloidosis)
Chronic inflammation or tissue destruction, most common, in cheetahs with helicobacter gastritis, secondary to chronic inflammation (prolonged elevation of SAA), can be idiopathic or due to non-immunologic neoplasia (paraneoplasia = not plasma cells)
Amyloid light chain (AL)
Derived from immunoglobulin light chain, associated with immunoglobulin secreting cells (B cells, plasma cells), usually primary amyloidosis
Amyloid-associated (AA)
Derived from serum amyloid A (SAA) synthesised in the liver and released during systemic inflammation (acute), usually secondary amyloidosis
A-β
Derived from amyloid precursor protein (APP), associated with amyloid angiopathy in Alzheimer’s and other forms of canine neurodegeneration
Familial amyloidosis
AA form - primarily deposits in kidneys - glomerular in cats, medullary in dogs, also in liver
Amyloid of ageing
A-β form - cerebrovascular amyloidosis in old dogs, may also deposit in heat, GIT and lungs
