Lymphoreticular system Flashcards
Glucocorticoids
Associate with binding proteins - transcortin and albumin
Following dissociation from binding proteins, passively diffuse into cell
Bind to a cytoplasmic receptor (under 3)
Conformational change of receptor unmasks DNA binding domain; associates with GREs following nuclear translocation
Cellular targets:
-Inflammatory cells: eosinophil, T cell, Mast cell, Macrophages, dendritic cell
- Structural cells: epithelium, endothelium, airway smooth muscle, mucus glands
Glucocorticoid - potential adverse effects
Central nervous systen - decreased mentation Musculoskeletal system - muscle wasting GIT Fluid, electrolyte balance Metabolic, endocrine immune systems - secondary infections Cats are more resistance that dogs
Chlorambucil
Rapidly metabolised to phenylacetic acid mustard
Slowest acting, least toxic of all alkylating agents
Myelosuppression generally not observed until administered for > 1 month
Urinary and faecal excretion
Administered without food
Azathioprine
Greater decrease of cellular than humoral immunity
Hepatic metabolism to active 6-mercaptopurine then to 6-thioinosinic, 6-thioguanylic, thiouric acids
Compete with endogenous adenine and guanine -> non-functional nucleic acid strands
Slow immunosuppressive effect
Haematological, gastrointestinal, hepatic +/- neuromuscular toxicity
Vincristine, vinblastine
Bind to tubulin, blocking polymerisation
Also break down pre-formed microtubules - increased release of PLTs from megakaryocytes
Both used in rxl of ITP (usually vincristine)
Can be given as bolus IV or to preload PLTs
Severe extravascular vesicants
Haematological, GI, neurological toxicity
Ciclosporin
Isolated from Cylindrocarpon lucidium and Trichoderma polysporum
Both IV and oral forms
Large volume of distribution: primary hepatic metabolism
Therapeutic drug monitoring - acute and chronic
Ketoconazole may be used to reduce costs
GI, renal, hepatic toxicity; also hirsutism, gingivial hyperplasia, papillomatosis +/- diabetogenic
Pathogenesis of immune-mediated disease
Immune system overeacts to normal body tissues or harmless exogenous proteins - loss of tolerance
Both humoral and cellular mechanisms of tissue damage recognied
Loss of self-tolerance is necessary to perpetuate+/- start disease
Trigger factors:
- release of sequestered antigens
- abnormal immunoregulation
- molecular mimicry
- polyclonal activation of T and B cells
- exposure of cryptic epitopes or haptenisation of foreign molecules to self antigens
Role of infection in immune-mediated disease
- Breakdown of vascular or cellular barriers allowing exposure of self antigens
- Promotion of cell death by necrosis, causing inflammation -> bystander activation
- Polyclonal activation of T cells - bacterial superantigens
- Molecular mimicry -> cross reactivity
Aetiology of immune-mediated disease
Often unclear, likely to be multifactorial
- Genetic, infectious and hormonal influences
Canine examples:
- SLE: genetics (DLA-A7; C4-4), C-type viruses
- IMHA: vaccinal antigens?
- Immune-mediated polyarthritis: vaccinal antigens?
Signalment of immune-mediated disease
Idiopathic immune-mediated disease over-represented in juvenile to middle-aged patients, through dogs and cats of any age may be affected
Vet examples:
- SLE
- Dogs from 2 months - 13y (GSDs, shelties, collies, beagles, poodles)
- Cats from 1-11y (Siamese, Persian, Persian-related breeds)
History/physical exam of immune-mediated disease
Generally characterised by remission and exacerbation
Lameness, mucocutaneous lesions, lethargy, dyspnoea, weight loss, PU/PD, +/- seizures or behavioural changes
Effusive, painful joints, cutaneous erythema, macules, papules, pustules, erosion etc., pallor +/- petechiae, cardiac arrhythmias
Lymphadenomegaly +/- splenomegaly
Diagnostic tests - CBC/coags
Immune-mediated disease
Anaemia - regenerative (IMHA) or non-regenerative (infection, uraemia, chronic bleeding, attack of precursors)
Thrombocytopaenia - Immune-mediated (I-M) thrombocytopaenia
Leucopaenia? anti-leucocytes antibodies e.g. SLE, I-M neutropaenia
Coagulation abnormalities: increase in APTT, PT,’anti-coagulant antibody’ (SLE), DIC
Diagnostic tests - chemistry panel
Immune-mediated disease
Azotaemia, increased inorganic phosphate - chronic glomerular lesions
Hypoalbuminaemia, hypercholesterolaemia - protein-losing nephropathy (PLN)
Hyperbilirubinaemia - pre-hepatic/haemolysis
Hyperglobulinaemia - inflammatory disease, polyclonal B cell activation
Increased creatine kinase and lactate dehydrogenase - polymyositis and/or myocarditis
Diagnostic tests - urinalysis
Immune-mediated disease
Proteinuria:
- PLN: r/o UTI and occult infection(s) e.g. Dirofilaria immitis, Ehrlichia canis, Anaplasma phagocytophilum, Borrelia burgdorferi, Rickettsia rickettsiae, Bartonella spp.)
Haematuria, pyuria, erythrocyte casts:
- r/o UTI and occult infections
- compatible with membranoproliferative GN
Diagnostic tests - radiography and arthrocentesis
Joint lesions are common in polysystemic IM disease, usually non-erosive pauciarthropathy
Erosive lesions suggest an overlap syndrome
Arthritis is not always clinically obvious
Synovial fluid: increased WBC, increased proportion of neutrophils +/- protein content with decreased viscosity and poor mucin clot formation
Coomb’s test
Immune-mediated disease
If acute IMHA suspected, in-saline agglutination and osmotic fragility tests may be performed
Antibodies associated with the surface of RBCs may also be detected with the Coomb’s test
Primary reagent: polyvalent anti-dog or anti-cat IgG, IgM and C3 antiserum (direct antiglobulin test)
False positive and negative reactions may occur
AChR autoantibodies
Immune-mediated disease
Acquired MG (myasthenia gravis): most common of immune-mediated neuromuscular disorders Various forms described: focal, generalised, acute fulminating, paraneoplastic 'Gold standard' for diagnosis of acquired MG is documentation of nicotinic AChR autoAb by immunoprecipitation RIA False positives v rare; 2% of dogs with generalised MG may be seronegative
ANA - antinuclear antibodies
Immune-mediated disease
Serum ANA - hallmark of human, canine and feline SLE
Indirect immunofluorescence or immunoperoxidase test
Substrate tissues have inc. rat liver, vero and Hep-2 cells; various pattern of staining
False positives and negatives may occur
Von Willebrand’s Factors (vWF)
Produced by endothelium and stored in Weibel Palade bodies
Also produced by platelets
Released early in the haemostatic process
Responsible for platelet adhesion to collagen
Platelets
Small discoid anuclear cells for in circulation
3-5 nanometres and are pale basophilic with small red granules
Derived from the cytoplasm of megakaryocytes in the bone marrow (thrombopoiesis)
Mediated by thrombopoietin
Circulate for 5-9 days in most species
Structure:
- Outer membrane contains receptors important for adhesion and aggregation
- Contain a cytoskeleton with actin and myosin that allows for shape change
- Contain membrane bound granules
Surface receptors:
- Glycoproteins associated with platelet membrane
- GP Ib - binds von Willebrand’s factor
- GP IIbIIa -binds fibrinogen on adjacent platelets and allows platelets to aggregate
- Defects in receptor lead to abnormal platelet function and clot formation
Primary haemostasis
Damage to the endothelium and exposure of subendothelial collagen
Von Willebrand’s factor is released from damaged endothelium
Platelet adhesion occurs
Platelet bind to collagen via receptor GPIb and vWF from the endothelium
Once platelets have adhered to collagen, they undergo shape change and become spherical with filopodia
Additional receptors for vWF (GPIb) and fibrinogen (GPIIbIIa) are exposed
Secondary haemostasis
Involves activation of the coagulation cascade
Happens simultaneously with formation of the platelet plus because damage to the endothelium releases tissue factor and activates the extrinsic coagulation pathway
Coagulation cascade
Extrinsic system - intiation
Most important in vivo Tissue factor (TF) released from damaged tissue binds and activates FVII in presence of calcium TF_FVII complex activates FX of the common pathway and FIX of the intrinsic pathway
Coagulation cascade
Intrinsic pathway - amplification
FXII is activated by contact with a negatively charged surface (cofactor HMWK)
Activated FXII cleaves and activates FXI which in turn activates FIX (calcium required)
Activated FIX i turn activates FX of the common pathway
Coagulation cascade
Common pathway
Starts with activation of Factor X
Activated FX binds activated Factor V and calcium on the platelet surface
This complex converts prothrombin (FII) to thrombin (FIIa)
Thrombin converts fibrinogen (FI) to fibrin (FIa)
Fibrin crosslinked by activated FXIII
Inhibitors of coagulation
Anti-thrombin III - inhibits thrombin and activated FX
Activity of ATIII increased by heparin from the endothelium
Protein C - inactivates Factors V and VIII
Fibrinolysis (enzymatic breakdown of fibrin by plasmin)
Immune-mediated thrombocytopaenia
Most common cause of thrombocytopaenia
Platelet numbers extremely low (often s syndome - concurrent immune mediated thrombocytopaenia and anaemia
Primary - antibodies produced against platelets antigens
Secondary - many causes (other immune diseases (SLE), drugs or vaccine, neoplasia, infectious)
Diagnosis of exclusion/response to treatment
Disorders of platelet function
Glanzmann’s thrombasthenia - defect in GPIIbIIIa
- Ottermans and Great Pyrenees, Quarter horse
- Defective platelet aggregation and abnormal clot retraction
Canine thrombopathia - abnormal GPIIbIIIa exposure and impaired degranulation - Basset hounds
Bovine thrombopathia - defect not know (Simmentals), mild to severe bleeding
Thrombocytosis
Physiological - transient - epinephrine induced splenic contraction
Reactive (secondary)
- Increased thrombopoietin and possibly IL6
- Inflammation, haemorrhage, iron deficiency
Essential thrombocytemia
- Myeloproliferative disorder
- Marked peristent incerase in platelets
- Bone marrow megakaryocytes increased and may have abnormal morphology
- Function variable - may see petechiae and ecchymoses or thrombosis
Von Willebrand’s disease
Clinical signs: mucosal bleeding (GI, epistaxis, haematuria etc.)
Bleeding may be absent
No petechiae - use to differentiate from other platelet disorders
See prolonged buccal mucosal bleeding time without thrombocytopaenia
Clotting time usually normal but PTT msy be prolonged due to decrease in factor VIII]
Common in dogs (rare in cats and horses)
Von Willebrand’s disease
Type I
All multimers are present but as decreased concentrations
Variable severity of bleeding but not until concentration of vWF are <20%
Most common - 90% cases
Dobermans
Autosomal inheritance so males and females equally affected
Von Willebrand’s disease
Type II
Qualitative abnormalities in vWF structure and function
Often disproportionate decrease in large multimers
Severe and uncommon
Seen in German short haired and wire haired pointers
Autosomal recessive