Immune mediated disease Flashcards
What percent of dogs with IMHA display a non-regenerative anemia on presentation?
30%
What are non-immune mediated causes of spherocytosis?
- Oxidative damage (zinc, acetaminophen)
- Pyruvate kinase deficiency
- Hypersplenism
- Envenomation
- Disorders associated with RBC fragmentation (endocarditis, hemangiosarcoma)
- Dyserythropoiesis
- Transfusion
How many spherocytes per hpf is supportive of IMHA?
> 5 per 100x field = 63% sensitivity, 93% specificity
3-4/hpf = 74% sensitivity and 81% specificity so can be suggestive of IMHA if other causes of spherocytes are eliminated
Is a PCV or hematocrit more reliable in cases of IMHA?
PCV - agglutination can falsely decrease the automated hematocrit
How is the saline agglutination test performed?
4 drops of saline, 1 drop of blood = 100% specificity
If results are equivocal, can wash the RBCs in saline (1:4 ratio) 3 times and see if agglutination persists
What is another name for a Coombs test?
Direct antiglobulin test (DAT)
What is the sensitivity and specificity of a Coombs test for the diagnosis of IMHA?
Sensitivity around 80%, specificity 95-100%
How does lipemia affect RBCs?
Increases erythrocyte fragility, which can increase artifactual hemolysis
What are the proposed mechanisms for the development of IMHA in dogs infected with B. gibsoni?
- Babesia infects RBCs, which may lead to antibodies targeting the organism destroying the RBC too
- Oxidative injury may lead to damage of uninfected erythrocytes, exposing antigens that are normally hidden
- Antibodies form against RBC membranes after silica acid residues are removed
Name two protozoan parasites other than Babesia that can trigger IMHA
Rangelia
Theileria
A high level of evidence exists for what organism causing IMHA in cats?
Mycoplasma haemofelis
What drug has the highest degree of evidence for inducing IMHA in dogs?
Cefazedone
What drug has the highest degree of evidence for inducing IMHA in cats?
Propylthiouracil
What are we supposed to call primary IMHA now?
Non-associative IMHA
Packed RBC transfusions given to dogs with IMHA should be no older than what? Why?
- 7-10 days
- Increased age of pRBC was associated with increased risk of mortality in dogs with hemolysis
Why are pRBCs preferred over bovine hemoglobin solutions for dogs with IMHA?
- BHS scavenge nitric oxide, potentially causing vasoconstriction and hypertension
- BHS exert a greater oncotic pressure, this increasing intravascular volume and hypertension
If a dog with IMHA is started on >2mg/kg/day of prednisone, when should the dose be decreased?
Within the first 1-2 weeks, as long as HCT is stable or increasing
What two clinicopathologic abnormalities were identified as predictors of mortality in IMHA patients?
Increased bilirubin
Increased BUN/urea
Does the consensus statement recommend IVIG?
Only as a salvage measure if a dog is not responding to 1-2 weeks of treatment with 2 immunosuppressive drugs
For IMHA patients, when should the dose of prednisone be tapered and by how much?
When the PCV is stable and >30% for 2 weeks after starting treatment, decrease prednisone by 25% (can decrease by up to 50% if on a secondary agent)
What monitoring should be performed while a patient is on azathioprine?
CBC and chem every 2 weeks for the first 2 months, then every 1-2 months
When are prophylactic antibiotics recommended for neutropenia?
<1000 cells/uL
In patients with severe neutropenia persisting for more than 1 week, what drug can be considered?
Recombinant granulocyte colony stimulating factor
What is the relapse rate for IMHA?
11-15% based on retrospective studies
Thromboprophylaxis should be provided to all dogs with IMHA except…
Dogs with severe thrombocytopenia (<30K)
What antithrombotic drug is recommended first for IMHA? If that isn’t available, what is recommended next?
- Unfractionated heparin with individual dose adjustment
- LWM heparin OR oral Xa inhibitor recommended second
How long should antithrombotics be continued in IMHA patients?
Until the patient is in remission and off prednisone OR until they have been in remission for 6 months with no other risk factors for thrombosis
In a retrospective study, what dog breeds were predisposed to developing PIMA?
Whippets, Miniature Dachshunds, Lurchers
What percent of dogs with PIMA ultimately responded to treatment? What was associated with improved survival?
- Erythroid regeneration in 88%, remission in 62%
- Corrected reticulocyte percentage >0.2 associated with improved survival
Cell free DNA was increased in dogs with IMHA compared to controls. What might cause this increase and why is it concerning?
- May be caused by cell death and release of neutrophil extracellular traps
- Cell free DNA has prothrombotic properties
What is a hallmark feature of bone marrow histopathology in dogs with PIMA?
Rubriphagocytosis
Dogs with PIMA develop a regenerative response after a median of how many days of immunosuppression? When is remission achieved?
Regeneration: 30 days
Remission: 60 days
What drug is capable of inhibiting canine complement-mediated hemolysis in vitro?
C1-esterase inhibitor
What cardiac biomarker is increased in dogs with IMHA on presentation and decreases with treatment?
Troponin I
Primary IMHA is most commonly diagnosed in what age cat?
2-6 years of age
What were negative prognostic indicators in cats with IMHA?
Higher bilirubin, older cats
What is IgG4 related disease?
Diffuse IgG4 positive lymphoplasmacytic infiltrates lead to increased serum concentrations of IgG4, peripheral eosinophilia, tumorous swellings, obliterative phlebitis, and fibrosis
What arm of the immune system mediates most autoimmune diseases?
Th2 cells - results in the production of autoantibodies
What antibody class is involved in most cases of IMHA? What is its half life?
IgG - half life is one week
How do glucocorticoids affect gene transcription?
- Enter the cell by passive diffusion
- Interact with glucocorticoids receptors in the cytosol
- Leads to a conformational change in the receptor and release of an activated complex => nucleus
- Activated complex binds to short DNA sequences called glucocorticoid response elements => modification of gene transcription
Name 5 ways that glucocorticoids suppress the immune system
- Inhibit production and release of cytokines, chemokines
- Impair macrophage activity by influencing the expression and function of Fc receptors
- Decrease macrophage antigen processing/presentation
- Reduce the numbers of lymphocytes
- Decrease migration of inflammatory cells from the blood into tissues
Describe the mechanism of action of cyclosporine
- Enters the cytosol and complexes with cyclophilin
- This complex then binds and inhibits calcineurin, thus inhibiting calcineurin’s calcium-stimulated phosphatase
- Without this dephosphorylation, NFAT is not activated
- NFAT is needed for nuclear transcription of cytokines, like IL-2
- IL-2 is needed for the activation and proliferation of T cells => inhibits T cell function
What enzyme metabolizes cyclosporine in the liver?
Cytochrome P450
When measuring blood cyclosporine levels, when should samples be obtained?
Peak - 2 hours after dosing
Trough - right before the next dose
What is the active metabolite of azathioprine?
6-mercaptopurine
What is the mechanism of action of azathioprine?
Purine analogue
- 6 mercaptopurine resembles adenine and guanine, so it is alternately inserted during the S phase of cell division
- Leads to ribonucleic acid miscoding => disruption of RNA and DNA synthesis and mitosis
Why are lymphocytes more sensitive to inhibition of purine and pyrimidine synthesis?
Lymphocytes lack a salvage pathway for the synthesis of purines and pyrimidine and are reliant on de novo synthesis of these nucleotides (unlike other cell lines)
What breed has lower thiopurine methytransferase activity and is therefore at higher risk of azathioprine toxicity?
Giant Schnauzers
What breed has higher thiopurine methytransferase activity and therefore may need higher doses of azathioprine to be effective?
Alaskan Malamute
What is the active metabolite of mycophenolate mofetil?
Mycophenolic acid
What is the mechanism of action of mycophenolate?
Inhibits inosine monophosphate dehydrogenase - enzyme necessary for de novo purine synthesis
- Inhibits both B and T cell proliferation/clonal expansion in the S phase of the cell cycle
- Suppresses B cell antibody formation
- Induces apoptosis of activated T cells
What isoform of inosine monophosphate dehydrogenase is primarily affected by mycophenolate?
Type 2 isoform (5 fold greater affinity) - found in activated lymphocytes
What nucleotide is primarily depleted by inhibition of inosine monophosphate dehydrogenase?
Guanosine
What is the mechanism of action of leflunomide?
Reversibly inhibits dihydro-orotate dehydrogenase - enzyme needed for de novo pyrimidine synthesis
What is the mechanism of action of alkylating agents?
- Cross-link DNA, thus interfering with DNA replication and RNA transcription
- Toxic to both resting and dividing cells (cell cycle nonspecific)
Name 2 alkylating agents that are commonly used for immune suppression in veterinary medicine
- Chlorambucil
- Cyclophosphamide
What metabolite of cyclophosphamide results in sterile hemorrhagic cystitis?
Acrolein
What drug has a primary immunosuppressive effect against macrophages?
Liposomal clodronate
What glucocorticoid has negligible mineralocorticoid activity and may be preferred in situations where water retention is detrimental?
Dexamethasone
In the bone marrow, how long does it take for erythroid precursors to differentiate into mature RBCs?
5-7 days
What is the half life of a RBC in dogs and cats?
Dogs: 100-120 days
Cats: 75 days
What causes excessive Heinz body formation?
Oxidative damage that denatures hemoglobin
Why are excessive Heinz bodies detrimental?
Increase RBC rigidity, thus increasing susceptibility to hemolysis
What is this abnormality?
Heinz body
Name two toxins that may result in Heinz body anemia in dogs?
Zinc, onions, acetaminophen
Name 3 conditions in cats that can increase the number of Heinz bodies present
- Diabetes mellitus
- Hyperthyroidism
- Lymphoma
How does hypophosphatemia result in hemolysis?
Decreased RBC ATP stores, leading to decreased membrane stability, increased osmotic fragility and increasing susceptibility to hemolysis
Name 2 genetic erythrocyte enzyme deficiencies that cause impaired erythrocyte energy metabolism => hemolytic anemia
Pyruvate kinase deficiency
Phosphofructokinase deficiency
In dogs with pyruvate kinase deficiency, progression iron overload from continuous hemolysis may lead to what?
Hemosiderosis and liver fibrosis
What causes sporadic hemolysis crises in dogs with phosphofructokinase deficiency?
Exercise-induced hyperventilation alkalemia
What cell line gives rise to hemophagocytic histiocytic sarcoma? What are the cells positive for on immunophenotyping?
Macrophages
CD11/CD18
What feline blood type develops high-titer antibodies against the other blood type in the first 3 months of life?
Type B cats develop anti-A antibodies that are hemolyzing and hemagglutinating
What is the effect of anesthesia on feline hematocrit?
Causes up to a 25% drop in hematocrit - don’t measure during anesthesia
What cells produce erythropoietin in the kidney?
Peritubular interstitial cells of the inner renal cortex and outer medulla
What inflammatory cytokine increases the production of hepcidin?
IL-6, primarily
How does hypocobalaminemia lead to anemia?
Deficiency of B12 inhibits purine and thymidylate synthesis => impaired DNA synthesis within erythroblasts => erythroblast apoptosis
What is ferritin?
The soluble storage form of iron in tissues
- Positive acute phase protein
- Representative measure of total body iron stores in health
What is transferrin? How is it measured?
- Main protein in the blood that binds and transports iron
- Measured indirectly and reported as total iron binding capacity
- Negative acute phase protein
Describe how an iron panel would look in a case of iron-deficiency anemia
- Serum iron level: low
- Ferritin level: low
- Transferrin (TIBC): normal to increased
- Iron saturation (serum iron/TIBC): less than 20%
- Bone marrow iron: low
Describe how an iron panel would look in a case of anemia of inflammation or chronic disease?
- Serum iron: low
- Ferritin: increased
- Transferrin (TIBC): normal to low
- Iron saturation: normal to low
- Bone marrow iron: normal to high
What is the lifespan of a platelet in circulation?
6-10 days
What cat breed develops Chediak-Higashi syndrome? What coat color occurs along with the disease?
Persians - blue smoke coat color due to partial albinism
What is Chediak-Higashi syndrome?
Primary immunodeficiency
- Recurrent neutropenia, neutrophil function defects, and platelet function defects
- Neutrophils and eosinophils contain abnormally fused granules
What causes Pelger-Huet anomaly?
- Autosomal dominant disorder
- Defective terminal granulocyte maturation leading to abnormal appearance but normal function
What dog breed is over-represented for Pelger-Huet anomaly?
Australian Shepherds
What is the appearance of granulocytes in Pelger-Huet anomaly?
Hyposegmented nuclei with mature chromatin
What causes leukocyte adhesion deficiencies, specifically type I LAD?
- Mutations in leukocyte adhesion proteins that prevent normal adherence and migration of WBC through the endothelium
- Type I = defect in the beta-2 integrin subunit (CD18)
Type I LAD has been described in what dog breed?
Irish Setters
What clinicopathologic abnormalities are observed in type I LAD?
- Marked peripheral neutrophilia with nuclear hypersegmentation
- Absence of neutrophils in tissues on biopsy
What are the clinical signs of type I LAD?
Puppies present with omphalitis followed by lymphadenopathy, low body weight, and febrile infections
What causes trapped neutrophil syndrome and what abnormalities are seen on a CBC and bone marrow biopsy?
- Neutrophils cannot leave the bone marrow normally
- Peripheral neutropenia with a degenerative left shift, marked monocytosis
- Myeloid hyperplasia in the bone marrow with increased mature neutrophils
Trapped neutrophil syndrome is autosomal recessive in what dog breed?
Border Collies
What phenotypic abnormality can be seen in Border Collies with trapped neutrophil syndrome?
Craniofacial deformity
Pyruvate kinase deficiency in dogs causes what changes to the bone marrow?
- Progressive myelofibrosis and osteosclerosis => bone marrow failure
- Likely due to iron overload and effects of prolonged increased erythropoiesis
What causes X-linked severe combined immunodeficiency?
Mutation in the common interleukin 2 receptor gamma chain - affects developing thymocytes
X-SCID is found in what dog breeds?
Cardigan Welsh Corgi and Basset Hound
What are the clinical signs of X-SCID?
Stunted growth, recurrent or chronic infections as maternal antibody production declines, dysplastic thymus, hypoplastic or absent lymphoid tissues
What clinicopathologic abnormalities are present with X-SCID?
Rare peripheral T lymphocytes, increased B lymphocytes
What causes autosomal recessive severe combined immunodeficiency?
Defective recombination events during T and B lymphocyte maturation - mutation in the catalytic subunit of DNA-dependent protein kinase
Autosomal recessive severe combined immunodeficiency has been described in what dog breed?
Jack Russel Terrier
What clinicopathologic abnormalities are present in autosomal recessive severe combined immunodeficiency?
Severe lymphopenia, decrease serum globulins, marked lymphoid hypoplasia (spleen, thymus, LN)
What causes cyclic hematopoiesis (or cyclic neutropenia)?
Autosomal recessive defect in trafficking of lysosomal membrane proteins
Cyclic hematopoiesis has been reported in what dog breed?
Gray Collies - grey coat color results from defect in melanocytes
What clinicopathologic abnormalities are found in cyclic hematopoiesis?
Neutropenia that occurs every 2 weeks
What abnormalities are found with common variable immunodeficiency?
Hypogammaglobulinemia, absence of B cells in lymph nodes, lymphocyte function deficits
What breeds are affected by common variable immunodeficiency and what infection do they commonly get?
Miniature Dachshunds and Cavaliers
Pneumocystis carinii pneumonia
What causes primary myelodysplastic syndrome?
Clonal disorders arising from mutations within hematopoietic stem and progenitor cells - as they are clonal, they are technically neoplastic disorders
What histopathologic changes on a bone marrow biopsy may increase the suspicion for primary MDS over secondary causes?
Increased immature precursors, higher percentages of dysplastic cells, megaloblastic erythroid precursors
Cyclosporine and prednisone suppressed expression of what inflammatory cytokines? Which drug suppressed them more?
IL-2 and IFN-gamma
Cyclosporine was more suppressive
What percent of dogs develop GI side effects from mycophenolate? What was the median time to onset?
25%, 10 days after starting the drug
What percent of dogs develop cytopenias from mycophenolate?
4%
What effect did 5-7 days of steroid administration have on cardiac changes in cats?
- Increased median left atrial and ventricular dimension
- No difference in absolute concentration of NT-proBNP but increased individual percentage change (60% of cats had a NT-proBNP that increased by 60% after treatment)
Suggests plasma volume expansion with steroids
What effect does desmopressin have on PU/PD in dogs receiving high dose glucocorticoids?
Decreased water intake, increased USG BUT caused hyponatremia
What dose of leflunomide is recommended and what dose increases the risk of side effects?
Recommended: 2mg/kg/day
Side effects: 3-4 mg/kg/day
What percent of dogs on immunosuppressive therapy develop opportunistic fungal infections? When do they occur?
- 13% overall - but 20% of dogs on cyclosporine developed them compared to 4% of dogs on other immunosuppressives
- Median of 43 days after starting treatment
Where do dogs on immunosuppressive therapy develop opportunistic fungal infections?
Majority are skin lesions, common on the distal extremities
What are the most common opportunistic fungal infections in dogs on immunosuppressives?
Soil saprophytes - phaeohyphomycoses and hyalohyphomycoses
In a retrospective study comparing mycophenolate/pred vs cyclosporine/pred, which group had better outcomes? Adverse effects?
- Similar outcomes (hospitalization time, 30 and 60 day survival)
- Cyclosporine technically had more adverse events, but it was 9 vs 11 dogs
In dogs with primary ITP, what clinical sign was associated with decreased survival to discharge?
Melena
In dogs with primary ITP, did anti-platelet antibodies correlate with response to treatment? With relapse?
- Persistence or percentage of APA was NOT associated with treatment response/survival
- But recurrence of APA WAS associated with relapse
What percent of dogs with primary ITP survive to discharge? What percent relapse and in what time frame?
89% survive to discharge
31% relapse, median of 79 days
In dogs with primary ITP that experienced a relapse, what percent experienced a second relapse?
50% - dogs that have relapsed once should be more closely monitored
Administration of what immunosuppressive drug increases the risk of neutropenia after vincristine in dogs with ITP?
Cyclosporine (OR 13)
In dogs with ITP, when does neutropenia develop after giving vincristine?
2-14 days, median 5 days
Do the immature platelets released after vincristine administration function as mature platelets?
Yes based on expression of P-selectin (CD62P) - marker of alpha granule release
What type of hypersensitivity reaction is thought to be involved in the development of non-erosive IMPA?
Type III hypersensitivity - immune complex deposition in the joint space, leading to neutrophil activation. Antigens may come from systemic circulation OR within the joint space itself
Describe type I hypersensitivity
IgE is bound to mast cells via the Fc portion. An allergen binds to and cross links the IgE molecules => mast cell degranulation
Describe type II hypersensitivity
IgG mediated cytotoxic hypersensitivity
- Cells are destroyed by bound antibodies, either through activation of complement or by a cytotoxic T cell with an Fc receptor for the antibody (ADCC)
Describe type IV hypersensitivity
Cell mediated - Th1 cells secrete cytokines that activate macrophages and cytotoxic T cells
In rheumatoid arthritis (erosive IMPA), what antibody has been found along the joint surface?
Antibodies against type II collagen
In rheumatoid arthritis (erosive IMPA), what characterizes the chronic persistent synovitis that occurs?
- Perivascular accumulation of mononuclear cells - possible type IV hypersensitivity
- T lymphocytes, macrophages, and fibroblasts release matrix-degrading enzymes (MMPs, etc) => cartilage damage
How long can it take for the erosive lesions in rheumatoid arthritis to appear on x-rays?
Up to 6 months - dogs with apparently non-erosive form should be re-evaluated
What are rheumatoid factors?
Antibodies directed against immunoglobulins (IgM, IgM, IgA)
What percent of dogs diagnosed with rheumatoid arthritis are positive for rheumatoid factors?
75%
Idiopathic IMPA can be subcategorized into 4 types. Name them
- Type 1 = no underlying disease
- Type 2 = reactive (infectious/inflammatory disease distant from the joints)
- Type 3 = enteropathic
- Type 4 = neoplasia-related
Why might GI disease lead to the development of IMPA?
Increased intestinal permeability may increase the amount of potential antigens accessing the blood stream => stimulates immune complex formation
What virus has been implicated in the development of IMPA, either after infection or vaccination?
Canine distemper virus
What dog breed may be predisposed to vaccine induced polyarthritis?
Akitas - 10% of puppies developed joint pain and cyclic fevers after vaccination
What dog breed may be predisposed to polyarthritis after receiving sulfonamides?
Dobermans
In cases of drug induced polyarthritis, clinical signs typically resolve within how many days of discontinuing the drug?
2-7 days
What is the typical signalment and presenting complaint of a dog with steroid responsive meningitis-arteritis?
- Medium to large breed, <2 years of age
- Acute onset neck pain, fever, lethargy
What does CSF analysis show in dogs with SRMA?
Inflammation, specifically increased IgA, and increased protein
Describe the pathogenesis of Shar Pei fever
- Shar Peis have an increased production of hyaluronic acid (HA) by dermal fibroblasts (leads to appearance)
- Degradation of HA by trauma/oxidative damage => smaller fragments that mimic microbial surface proteins
- Leads to the release of IL-1beta, IL-6, and inflammation
What is the mechanism of action of colchicine?
Thought to impair the release of serum amyloid A from the liver by binding to hepatocyte microtubules and preventing amyloid secretion
What cell type is more common in the synovial fluid of dogs with erosive IMPA compared to non-erosive IMPA?
Lymphocytes
What joints are most commonly affected by erosive IMPA?
One paper says carpal joints
What marker of oxidative stress is found in anemic dogs (all causes of anemia)?
Decreased glutathione peroxidase activity
In dogs with IMHA undergoing necropsy, what percent displayed evidence of thrombus formation?
50-80%, depending on the study
What are the mechanisms driving hypercoagulability in IMHA patients? What is not responsible?
- Increased tissue factor expression
- Platelet activation
- Procoagulant microparticles
- Neutrophil NETs
NOT: antiphospholipid antibodies
