Immunology/haematology Flashcards
Cyclophosphamide mechanism of action?
Alkylation (cross linking) of DNA in S phase.
T and B cell lymphopenia, suppresses T cell activity and AB production
Acrolein bladder tox.
Azathioprine mechanism of action?
Purine analogue, metabolised to ribonucleotide monophosphates (6mercaptopurine) and inhibits enzymes required for purine biosynthesis. DNA incorporation causes RNA miscoding.
Humoral > cell mediated immunity. Decreases lymphocyte activation and proliferation (lack of purine salvage pathway). Decreases macrophage function.
Active form metabolised by thiopurine methyltransferase and xanthine oxidase.
Relevant breeds and medications for azathioprine use?
Giant schnauzer/cat - low TPMT activity. Malamute - high TPMT activity. Allopurinol inhibits XO.
Methotrexate mechanism of action?
Inhibits (competitive) folic acid reductase - no purine/pyrimidine synthesis. Mostly S phase.
Glucocorticoid mechanism of action?
Cytosolic glucocorticoid receptors (vary with tissue), glucocorticoid response elements, gene transcription.
Stabilise endothelial membranes, decrease chemotactic factors/cytokines/adhesion molecules. Inhibit arachidonic acid release.
Dose dependent, cellular/humoral.
Decrease pro inflamm cytokines, complement function, T cell proliferation/AB production, macrophage Fc receptors
Increase anti inflamm cytokines
Redistribute mono/lymphocytes, mainly T, to bone marrow and lymphatics.
How much mineralocorticoid activity do the various steroids have in comparison to cortisol?
Prednisolone 0.3 - 0.8
Dex 0
Hydrocortisone 0.8 - 1
Cyclosporin mechanism of action?
Cyclosporin/cyclophilin compleex binds and inhibits calcineurin. Impedes calcium dependent signal transduction/dephosphorylation, impedes activation of nuclear factors of activated T cells. No nuclear transcription of IL2 so decreased T cell activation/proliferation.
Cytotoxic T cell activity decreased.
Stimulates TGFbeta production which inhibits IL2-stimulated T cell proliferation and generation of antigen-spec cytotoxic T cells.
NB need ultramicronised microemulsion (better absorption)
Cytochrome p450 metab, biliary excretion. Peak conc 2h
Pharmacodynamic evaluation measures IL2 and IFN gamma.
Hepato-nephrotixicity v uncommon
Side effects of ciclosporin?
Secondary inf gingival hyperplasia hirsutism
Tacrolimus mechanisms of action?
Similar to cyclosporin - FKbinding protein complex, decrease T cell activation.
Does B and T cells and ABs. More potent than cyclosporin.
Mechanisms of action of sirolimus/rapamycin?
mTOR inhibition
(T cell G1 - S, cyclosporin G0 - G1)
T and B cells
Mechanism of action mycofenolate?
Hydrolysed to mycophenolic acid by the liver (active form).
Inhibits inosine monophosphate dehydrogenase in activated lymphocytes (needed for de novo purine biosynthesis). Prevents guanosine and deoxyguanosine biosynthesis.
Inh B and T cell proliferation. Decrease AB production. Apoptosis activated T cells. Humoral and cell med immunity, decrease adhesion and lymphocyte/mono recruitment
Hepatic glucuronidation inactivates to mycophenolic acid glucuronide which is excreted in bile (intestine flora deglucuronidate so get second peak). 90 % excreted in urine as MPAG.
Leflunomide mechanism of action?
Inhibit de novo PYRAMIDINE synthesis. Dihydroorotate dehydrogenase inhibitor.
B and T lymphocyte - decrease proliferation, decrease leucocyte adhesion, decrease IgG synth.
Activates by intestinal mucosa/liver to teriflunomide.
Renal excretion of trimethylfluoroanaline - susceptible tox if renal insufficiency.
Chlorambucil mechanism of action?
Non cell cycle specific alkylating agent. Cross links DNA. Inhibits resting/dividing cells, esp lymphocytes - cell and humeral immunity inhibition.
Inactivated by the liver
How are RBCs destroyed in extravascular/intravascular haemolysis?
Extra - macrophages in spleen
Intra - complement mediated - IgM ABs activate
Antierythrocyte ABs from B cells, but T cell (CD4 driven disease)
What genetic factors are there for development of IMHA?
Breed - cocker spaniel, familial association
Autoreactive T cells in siblings
DLA haplotype?
Most common antigen in IMHA?
Anion exchange molecule/erythrocyte membrane glycoproteins
What seasons is IMHA most common in?
Spring and early summer
Percentage of idiopathic IMHA?
70 - 80 %
What antibodies are most common canine IMHA?
IgG or IgG plus IgM (rare to have only IgM)
Increased pro-inflamm cytokines IMHA?
Monocyte chemoattractant protein 1, GMCSF (assoc with mortality also IL15 and 18)
Why might thromboembolism occur in IMHA?
DIC - evidence present 50 %
What do platelets express more of in IMHA?
P-selectin - activation (driven by cytokines)
Negative prognostic indicators canine IMHA?
Hyperbilirubinemia, thrombocytopenia, leucotyosis with left shift, azotaemia, hypoalbuminaemia, intravascular haemolysis, prolonged hyperlactataemia hepatic insufficiency, macrophage activating cytokines, autoagglutination, increased aPT.
What is NOT associated with IMHA outcome?
Degree of anaemia, magnitude reticulocyte response (1/3 present non-reg), degree of spherocytosis
Why would you use LMW and not unfractionated heparin?
Latter more likely to cause iatrogenic coagulopathy (thrombin and Xa). LMW less protein bound and more stable pharmacokinetic.
Mechanism of heparin action?
Binds AT, enhances its activity, inhibit factor II and X. CRI required for efficacy?
LMW only does Xa not thrombin. Need to monitor this factor to assess efficacy, can’t use aPTT.
Variable between individuals, goal appt 1.5 - 2.5 x RI
Does ultralow dose aspirin have an anticoagulant effect?
Not in healthy dogs. Single 5 - 10 mg/kg dose inhibits platelet function in healthy dogs.
BUT ultralowdose aspirin was associated with improved outcome in dogs with IMHA.
Clopidogrel target?
Platelet P2Y12 (ADP receptor) - block aggregation
Survival benefit of aspirin versus clopidogrel IMHA?
No difference, even if clopidogrel loaded. No difference if drugs added together.
Benefits of glucocorticoids in IMHA?
Suppress macrophage function
Decrease T cell activity (therefore decrease B cell stim and AB production) and induce lymphocyte apoptosis
Evidence for secondary immunosuppressive drugs in IMHA?
One study found superior survival with azathioprine, otherwise no evidence to add secondary
Platelet count in greyhounds?
Can be lower than other breeds
In what infectious diseases have anti platelet antibodies been detected?
Ehrlichia canis, Rickettsia. rickettsii (RMSF), A phagocytophilum, Babesia, Lepto, Leishmania
Most likely causes of moderate to severe thrombocytopenia?
ITP, overwhelming sepsis, E canis
RBC life span in cats and dogs?
70/120 days
Indirect/direct platelet autoantibody?
Indirect - AB in serum, direct - AB on platelet/megakaryocyte surface
Direct more specific
When is splenectomy contraindicated in ITP?
Haemoparasite infections - can exacerbate and associated with resistance antiprotozoal therapies.
ITP negative prognostic indicators?
Severe bleeding with anaemia, intracranial haemorrhage, melaena/increased urea
NOT platelet count
Most common antigen in ITP?
Fibrinogen receptor (GPIIb/IIIa)
Decrease in Treg cells implicated
ITP associated with recent vaccination?
NO!
one case report distemper
What Ig is on platelet in ITP?
IgG (present in 77 % ITP, 100 % B gibsoni…)
Increases with age of sample
Evidence for secondary therapies in ITP?
IVIg and vinc equally shorten time to platelet recovery and hospitalisation
One case series mycophenolate mono therapy
No evidence for other secondary agents
Platelet decrease significance in IMHA?
< 50, 76 % mortality 30 d
< 15, 25 % mortality (not different IMHA alone)
Cats and IMT?
Only around half respond to pred alone - need secondary. Frequent relapse. Long term immunosuppressive.
What influences BMBT other than platelet number and function?
Haematocrit, blood viscosity
What PFA time is best for vWD?
Collagen/ADP, > 120 s
Also impacted by BMBT factors
What % of vWF is normal?
70 - 180 %, < 50 abnormal
What might falsely increase and decrease vWF?
Decrease - haemolysis
Increase - pregnancy/parturition/inflammation/sepsis
Type 1 vWD?
Partial quantitative deficiency - Doberman, Irish setter. GSD, BMD - all same mutation, autosomal recessive
Type 2 (A) vWD?
GSH/WHP, collie, Chinese crested Auto recessive
Loss HMW protein, need to demonstrate decrease collagen binding activity (ratio with Ag:binding >1)
Type 3 vWD
Complete lack of factor. Dutch koiker, scottie, sheltie.
Auto recessive, various mutations
Inheritance pattern of congenital coagulation factor deficiencies?
Haemophilia A and B (8 and 9) X linked recessive
I, II autosomal
VII, X, XI, XII autosomal recessive
Changes in clotting times with coagulation factor deficiency?
PTT and PT: I, II, X
PT: VII
PTT: VIII, IX, XI, XII
Do dogs have vWF in their platelets?
No, only endothelium
Does factor activity influence clinical severity in canine type 1 vWD?
Controversial - one source says yes one says no
What haemophilia is most common? What haemophilias affect breed/species?
Dogs and cats. A most common. Many breeds.
What percentage of factor activity correlates with most bleeding in haemophilia?
Severe < 2 %, mild to moderate 2 - 20 %
Normal = 50 - 150
Breeds for congenital factor I deficiency?
Fibrinogen - dogs (borzoi, collie, bichon) and cats
Breeds for congenital factor VII deficiency?
Initiates coagulation by interacting with tissue factor.
Beagles, deerhounds (same mutation) - mild.
More severe malamutes and cats.
Breeds for congenital factor XI deficiency?
Kerry blue, springer, cats
Mild haemorrhage
Breeds for congenital factor XII deficiency?
Haegman. Cat. Activates intrinsic pathway in vitro not required for fibrin formation in vivo. No clinical consequence.
What are the labile clotting factors?
V and VIII
What is in cryoprecipitate?
vWF, VIII, I, fibronectin, XIII
What is in cryosupernatant?
Everything but vWF, VIII and I
How does tranexamic acid work?
Antifibrinolytic. Lysine analogue, inhibit plasmin activation.
What is the main stimulus for thrombin formation in DIC?
Tissue factor:VIIa complex. Activates factor IX (intrinsic) and X (common pathway)
How might DIC occur in systemic inflammation?
Monocytes express tissuee factor, anticoagulant system impaired, PAI-1 (plasminogen activator inhibitor) mediated fibrinolysis inhibition,
What does antithrombin inactivate?
II, TF:VII, IX, X, XI
Also binds cellular receptors on neutrophils/monos, stim antiinflamm/antiplatelet prostacyclin production
AT depletion (consumption in AT thrombin complex, degradation by neutrophil elastase, decreased hepatic synthesis, loss due to capillary permeability) factor in DIC
When should DIC be anticipated
Hypotension, impaired organ blood flow, SIRS, vasoactive agent release
What is a sensitive test for DIC?
D - dimer - 95 % sensitive
How does the endothelium protect against thrombosis?
Thrombomodulin binds thrombin and allows it to activate protein C, C associates with S.
CS: inactivates V and XIII
Endothelium produces prostacyclin under thrombin influence - inhibits platelet aggregation.
Tissue plasminogen activator causes fibrinolysis.
How might fibrinogen change haemostasis?
Increased in inflammation. Increases blood viscosity and RBC aggregation - decreased blood flow. Increases velocity of platelet aggregation and increases platelet reactivity. Denser clots, more resistant to fibrinolysis.
Why might aspirin be ineffective in dogs?
Aspirin acts through decreasing thromboxane A2 formation and therefore increasing platelet activation for its lifetime. Thromboxane is G protein mediated and 70 % normal dogs have a defect in the G protein signalling.
High dose or low dose aspirin for ATE in cats?
Low dose is fine as no diff in recurrence, fewer GI effects
What factors might affect TEG/ROTEM?
Hypocoag - increased PCV/decreased platelet
Hypercoag - decreased PCV/increased fibrinogen, storage
How sensitive are PT/aPTT?
Need factor activity to be decreased by 30 - 50 % to be abnormal
What affects PT?
Tissue factor (extrinsic) and common pathways.
VII, X, V, II, I
What affects aPTT?
Contact (intrinsic) and common pathway.
VIII, IX, X, V, II, I.
What would you measure with the Clauss method?
Fibrinogen.
Could also measure with thrombin time.
What is the difference between FDP and D dimers?
D dimers are only present if there has been fibrin crosslinking.
D dimers have short half life approx 5h.
Why is thrombin antithrombin ELISA measurement useful?
Thrombin has a short half life, TAT stable. Increased HAC/neoplasia/blastomycosis.
Why are animals with IMHA hypercoagulable?
RBC membrane phosphatidylserine exposed.
Monocytes express tissue factor.
Systemic inflammatory state increased platelet reactivity.
What are most IMHA deaths causes by?
Thrombosis, pulmonary most common
Does albumin correlate with risk of thrombosis in PLN?
PLN - other factors for hypercoag other than AT - platelet reactivity/fibrinogen increase/fibrinolysis decrease.
Albumin might be a marker of thromboembolic risk but doesn’t always correlate with hyper coagulability and AT. Can be hypercoag with normal albumin.
14 - 27 % PLN get thrombosis
PLE and thrombosis?
Decreased AT and evidence of hypercoagulability. Clinical thrombosis low but unpredictable - can happen when improving.
What is the most common cause of PTE?
Neoplasia
What enzyme do anticoagulant rodenticides inhibit?
Vitamin K epoxide reductase (reduces vitamin K epoxide so it can act with gamma glutamyl carboxylase to carboxylate clotting factor precursors)
Vitamin K dependent clotting factors? One with shortest half life?
2, 7, 9, 10, protein C and S
7 shortest half life
When does PT change after rodenticide intox?
36 - 72h
PIVKA at 12h
What are acquired anticoagulants?
Antibodies directed against clotting factors, usually IgG.
Example - lupus anticoagulant - antiphospholipid protein AB - inhibits coag factor/cell membrane interaction - increased PTT
Scott syndrome?
GSD, lack of externalisation of phosphatidylserine - get coagulopathy as membrane surface cannot support plasma coagulation factor activity
Autosomal recessive.
Get epistaxis not petechia/ecchymoses. Prothrombinase activity required for nasal arterial microcirculation?
Flow cytometry can measure PS externalisation
How would the corrected reticulocyte count be calculated?
Divide retic count x hct by normal hct
How long does it take for a rbc precursor to develop through to RBC?
5-7d
How long do reticulocytes stay in the bone marrow for?
2-3d
What effect does EPO have on the cell red composition?
More retics and latestage polychromatophilic erythroblasts (normoblast)
What result would you expect from Coomb’s/osmotic fragility test in haemophagocytic syndrome?
Negative both
Why does hypophosphataemia cause haemolysis?
Decreased membrane stability (interference with energy metabolism), so more osmotic fragility and susceptibility to oxidative stress.
When would a Coomb’s test be positive in Babesia?
Gibsoni/vogeli
Most sensitive test for Babesia?
PCR
Retroviruses and mycoplasma?
Increased risk for mycoplasma
When do anti-erythrocyte antibodies develop in mycoplasma infection?
After the onset of anaemia
Pyruvate kinase deficiency?
Autosomal recessive, progressive iron overload might cause haemosiderosis/hepatic fibrosis.
Can occur in cats and dogs. Cats dx old dogs young.
DOGS - progressive myelofibrosis due to iron overload./prolonged haematopoiesis.
Phosphofructokinase deficiency?
Springer spaniels. Autosomal recessive. Not cats.
Exacerbated by exercise (alkalaemia - haemolytic crisis)
What markers are usual for histocytic sarcoma?
CD 11 and CD 18
Macrophage derived
Where is EPO made?
Peritubular interstitial cells under the influence of hypoxia inducible factor
Also liver - may be increased with hepatic injury
What might increase hepcidin?
Positive acute phase protein so IL6, also decreased renal clearance can increase
Transferrin?
Negative APP, TIBC
Iron deficiency saturation percentage?
Iron/TIBC < 20 %
What is important about EPO analogues?
Aim low end RI to minimise hypertension, have to give iron concurrently.
Darbo give less often, and less likely to form antiEPO ABs, but more expensive.
What hormones stimulate erythropoiesis?
T4, glucocorticoid, growth hormone
How should a polycythaemic dog with a concurrent PDA be managed?
PCV maintained higher due to hypoxaemia
GPIIIb/IIa?
Fibrinogen receptor
GPIb?
vWF receptor
GPVI?
Collegan receptor on platelet
Where is thromboxane A2 from?
Phospholipase A2 in platelet > arachidonic acid on activation > COX 1 makes into thromboxane A2
Alpha granules platelet?
Some vWF in cats, fibrinogen, factor V/XII, P selectin
Dense granules platelet?
ADP, calcium, serotonin
Does DDAVP increase HMW vWF?
Increases vWF a little in type 1 but not more HMW in dogs
Acquired vWD?
CKCS with mitral valve disease (decrease factor and loss HMW multimer),
Also SAS
vWD in cats?
Both type 3 in case reports
Greater Swiss mountain dog platelet disorder?
P2Y12 receptor - impairment of ADP binding.
Autosomal dominant. No spontaneous bleeding.
Glanzmann thrombasthenia?
Otterhound and Great Pyrenees, two different mutations, autosomal recessive.
Absence of the fibrinogen receptor (GPIIb/IIIa) - get spontaneous bleeding.
Also described in a male cat with integrin subunit alpha IIb gene mutation.
CaIDAGGEFI thrombopathia?
Prevents GPIIIb/IIa conformational change for fibrinogen binding. Spontaneous mucosal bleeding.
Basset, spitz, landseer. Recessive.
Cyclic haematopoiesis?
Grey collie. Autosomal recessive.
Cyclic neutropenia/stem cell deficit. Defect trafficking lysosomal membrane proteins. Neutrophils deficient in neutrophil elastase and myeloperoxidase.
Platelet storage pool disorder - serotonin/ATP/ADP deficiency (dense granules).
Cannot phosphorylate intracellular proteins so lack of platelet activation by collagen, thrombin etc.
LAD I/II?
GSD, impaired integrin activation on platelets.
Chediak Higashi syndrome?
Lack of dense granules in platelets.
Recurrent neutropenia with neutrophil function defects.
Leucocyte/melanocyte abnormalities. Persian (blue smoke). See abnormally fused granules in neut/eos/other cells.
C-GSF might partially correct neutrophil function.