Immunology and Hematology CVT Flashcards
What is the MOA of cyclophosphamide?
o Alkylation of DNA during the S phase in cell cycle → Can be lethal to cell or produce miscoding errors (inhibit cell replication or DNA transcription)
§ Produces T- and B-cell lymphopenia
§ Suppresses both T-cell activity and antibody production
What are the indications for cyclophosphamide in dogs and cats?
· Indications in Dogs: Corticosteroid-resistant IMHA or IMTP, Rheumatoid arthritis; Polymyositis (in conjunction with corticosteroids)
· Indications in Cats: IMHA; Rheumatoid arthritis
What are the side effects of cyclophosphamide?
Myelosuppression; Gastroenteritis; Alopecia; Hemorrhagic cystitis
What is the MOA of azathioprine?
o Purine analog that is metabolized to ribonucleotide monophosphates → Poor conversion to diphosphates and triphosphates → ↑intracellular monophosphates → feedback inhibition of the enzymes required for biosynthesis of purine nucleotides
§ Triphosphate analogs formed → incorporated into DNA → ribonucleic acid miscoding and faulty transcription
§ Greater effect on humoral immunity
What are the indications of azathioprine in dogs?
Indications in Dogs: IMHA (administered in conjunction with steroids and/or cyclophosphamide); IMTP; Autoimmune skin disease; Chronic Hepatitis; Myasthenia Gravis; IM Glomerulopathy; Chronic Atrophic Gastritis; SLE; Inflammatory Bowel Disease
What are the indications of azathioprine in cats?
**VERY Myelotoxic in cats**
What are side effects of azathioprine?
Bone Marrow Suppression: Leukopenia, anemia, thrombocytopenia; Acute pancreatitis; Hepatotoxicity
What is the MOA of methotrexate?
o Competitively inhibits folic acid reductase (necessary for reduction of dihydrofolate →tetrahydrofolate) → affects production of purines and pyrimidines
§ Manifest during S phase (cell cycle)
What are the indications or methotrexate in dogs and cats?
Antineoplastic in lymphoma, carcinomas, sarcomas
What is the major side effect of methotrexate?
Gastrointestinal toxicity
How do glucocorticoids work?
o Glucocorticoids stabilize cell membrane of endothelial cells
o Inhibits:
§ Production of local chemotactic factors (¯ infiltration neutrophils, monocytes, and lymphocytes)
§ Secretion of destructive proteolytic enzymes (collagenase, elastase, and plasminogen activator; in allogeneic tissue)
§ Release of arachidonic acid from membrane phospholipids → prevents synthesis of prostaglandins, thromboxanes, and leukotrienes (major mediators of inflammation)
o Redistribute monocytes and lymphocytes from peripheral circulation to lymphatics/bone marrow (affects primarily T cells)
o Decrease T-cell activation and cytotoxicity
o Decrease Cytokine activity
o Alter macrophage function
What is the MOA of cyclosporine?
· Bound in cytosol (lymphocytes) by cyclophilins (cyclosporine-binding proteins)
o Cyclosporine-cyclophilin complexes → calcium-dependent calcineurin-calmodulin complexes → impede calcium-dependent signal transduction
§ Transcription factors → promote cytokine gene activation are direct or indirect substrates of the serine-threonine phosphatase activity of calcineurin
§ Enzymatic activity ¯ by association of cyclosporine-cyclophilin bimolecular complex with calcineurin
§ Inhibits early T-cell activation (G0 phase of the cell cycle)
§ Prevents synthesis of several cytokines (IL-2)
§ Without IL-2 → further T-cell proliferation is inhibited (T-cell cytotoxic activity ¯)
§ Stimulates cells to secrete transforming growth factor–β (TGF-β) protein → potent inhibitor of IL-2–stimulated T-cell proliferation and generation of antigen-specific cytotoxic lymphocyte
o NOT cytotoxic or myelotoxic
Which immunosupressant is specific for lymphocytes?
Cyclopsorine (specificity spares other rapidly dividing cells; allows nonspecific host defense to continue to function)
What is a potential reverse effect of cyclosporine in cats?
Can be nephrotoxic
What is the MOA of tacrolimus?
Binds in cytosol (lymphocytes) with an immunophilin, FK-binding protein (FKBP) → tacrolimus-FKBP complex binds to calcineurin and inhibits its phosphatase activity→ directly and indirectly inhibits de novo expression of nuclear regulatory proteins and T-cell activation genes o Transcription of cytokines (IL-2, IL-3, IL-4, IL-5, interferon-γ, TNF-α, and granulocyte-macrophage colony-stimulating factor) responsible for lymphocyte activation is suppressed
o ¯ IL-2 and IL-7 receptors
o Inhibits B-cell proliferation/production of antibody (unknown mechanism)
What are the indications of tacrolimus in vet med?
o Topically: 0.1% solution, controlled discoid lupus erythematosus and pemphigus foliaceus in dogs (Rosenkrantz et al., 2004)
o Topical 0.02% aqueous suspension for the effective treatment of dogs with KCS (Berdoulay, English, and Nadelstein, 2005)
What is the MOA of sirolimus?
· Macrocyclic antibiotic with a structure similar to tacrolimus → binds in cell cytosol to FKBP
o Affect different and distinct sites in the signal transduction pathway
o Immunosuppressive → sirolimus-FKBP complex blocking activation of target of rapamycin, (mTOR)
§ mTOR is serine/threonine protein kinase →regulation of cell proliferation through the initiation of gene translation in response to AA, growth factors, cytokines, and mitogens
§ Kinase activity of cyclin-dependent kinase-2 and cyclin-dependent kinase-4 (cell cycle regulators) also inhibited
§ Blocks IL-2 and other growth factor–mediated signal transduction (signal 3 of the allograft rejection response) and the calcium-independent CD28/B7 (CD80/CD86) costimulatory pathway
□ Cyclosporine and tacrolimus block T-cell cell cycle progression at the GO to G1 stage
□ Sirolimus prevents cells from progressing from G1 to the S phase
® Blocks T-cell activation by IL-2, IL-4, and IL-6 and stimulation of B-cell proliferation by lipopolysaccharide
® Directly inhibits B-cell immunoglobulin synthesis caused by interleukins
What are potential side effects of sirolimus?
hyperlipidemia, thrombocytopenia, delayed wound healing, delayed graft function, mouth ulcers, pneumonitis, and interstitial lung disease
What is the MOA of mycophenolate?
o Prodrug hydrolyzed by liver esterases → mycophenolic acid
o MOA:
§ Cytostatic for lymphocytes → inhibition of inosine monophosphate dehydrogenase → enzyme necessary for de novo purine biosynthesis
o Relatively selective inhibitor of T- and B-cell proliferation during the S phase of the cell cycle via its ability to prevent guanosine and deoxyguanosine biosynthesis
What is the MOA of leflunomide?
· Synthetic organic isoxazole → intestinal mucosa metabolizes to active form = A77 1726
· Part of its antiproliferative activity during the S phase (cell cycle) → inhibiting de novo pathway of pyrimidine biosynthesis
o Target: enzyme dihydroorotate dehydrogenase
What is a potential side effect of leflunomide in dogs?
o GI toxicity (dogs) → accumulation of metabolite trimethylfluoroanaline (TMFA)
§ Cats: TMFA does not present the toxicity problem encountered
What is FTY 720?
from myriocin (fungus-derived sphingosine analog) o After phosphorylation, FTY 720 engages lymphocyte sphingosine-1-phosphate receptors and profoundly alters lymphocyte trafficking → acting as a functional sphingosine-1-phosphate antagonist o Sequesters naïve and activated CD4+ and CD8+ T and B cells from the blood into lymph nodes and Peyer's patches (without affecting function) o Does not impair cellular or humoral immunity to systemic viral infection nor does it affect T-cell activation, expansion/proliferation, or immunologic memory o Synergizes effectively with inhibitors of T-cell activation and proliferation to prevent allograft rejection
Is there alloantibody production in dogs?
NO! · No clinically important alloantibodies (isoantibodies) present before sensitization with a transfusion
· Pregnancy does not cause sensitization because of a complete placenta in dogs → NO alloantibody production
What is the most antigenic blood type in dogs?
DEA 1.1
Anti-DEA 1.1 antibodies will develop after 4 days
What is the universal blood donor in dogs?
DEA 1.1 Negative
Does pregnancy sensitize dogs to develop alloantibodies?
No!!
What is the most common DEA in dogs?
DEA 4 - Positive in >98% of dogs
What is the universal blood donor in cats?
There is NO universal blood donor in cats
What are the 3 major blood types of cats?
o Type A (a/a or a/b)
o Type B (b/b)
§ 40% British shorthaired, Devon rex (A-B incompatibility → heterozygous kittens)
§ None in Siamese
o Type AB (rare): 3rd allele (AB), recessive to “a” and codominant to “b” – both expressed
§ Purebred and DSH known to have type B blood (DNA tests available) → < 1%
Do cats have alloantibodes to blood types?
Yes! o Cats lacking certain antigen in RBC may have naturally occurring/induced alloantibodies (isoantibodies) against the missing type → acute hemolytic transfusion rxn and anti-A mediated hemolysis of newborn (neonatal isoerythrolysis)
What is another RBC antigen in cats?
o Mik antigen: Most but not all DSH
o Mik-positive blood to cats lacking Mik antigen → acute hemolytic transfusion reactions
o Naturally occurring anti-Mik alloantibodies documented in several Mik-negative cats
When blood typing a cat that is severely anemia, but there is no agglutination on the card what could be happening?
Severely anemic cats may not agglutinate → excess antibody present compared to the number of red cells → prozone effect
What is the big difference between dogs and cats in blood typing?
Cats possess naturally occurring alloantibodies against the blood type antigen they lack o All type B cats: strong anti-A antibodies with high hemolysin and agglutinin titers (>1:32) after a few weeks of age
o Type A cats: weak anti-B alloantibodies with low anti-B titers of 1:2
Which species can have neonatal isoerythrolysis?
Cats! o Kittens (Type A, AB) receiving anti-A alloantibodies through colostrum from type B queens (including primiparous queens), during the first 16 hours of life → neonatal isoerythrolysis
§ Dark pigmenturia, anemia, icterus, anorexia, and sudden death (first week of life)
§ Survivors may develop tail tip necrosis
Why is crossmatching important?
§ Reveal blood group antigens on RBC surface → serologic compatibility/incompatibility btwn donor and recipient
o Check for presence/absence of naturally occurring/induced alloantibodies in serum (or plasma)
o Abs may be hemolysins and/or hemagglutins (directed against known blood groups or other RBC surface antigens)
Describe a major crossmatch.
Alloantibodies in recipient’s plasma against donor RBCs o Incompatibility→ greatest importance: predicts that transfused donor cells will be attacked by antibodies in patient’s plasma → acute hemolytic transfusion rxn (can be life threatening, with as little as 1 ml)
Describe a minor crossmatch.
Alloantibodies in donor’s plasma against the recipient’s RBCs o Incompatibility → lesser concern: donor’s plasma volume is small (esp pRBCs) and plasma markedly diluted in the patient
What can be added to a crossmatch to enhance the reaction?
Coomb’s reagent (anti-IgG, anti-IgM, anti-C3)
What can occur in a dog that is receiving its first transfusion?
should be compatible (No clinically important naturally occurring alloantibodies) → May omit a crossmatch if 1st transfusion (as long as the donor has also not be transfused)
What should occur in a dog that has received a previous blood transfusion?
§ Compatible crossmatch does NOT prevent sensitization of patient against donor cells (in 1-2 wks)
□ Thus previously transfused dogs should ALWAYS be crossmatched (even if receiving blood from same donor)
® This transfused dog should NEVER be used as a donor
What is the time span from initial transfusion to incompatibility?
4 days (risk may last for years due to alloantibodies)
What should occur in a cat that is receiving its first transfusion?
§ First crossmatch may be incompatible (naturally occurring alloantibodies) → Due to anti-A alloantibodies, anti-B alloantibodies, Mik alloantibodies, or rxn to other RBC antigens
= Needs crossmatch
What should be considering when thinking about giving a plasma transfusion in a cat?
§ Naturally occurring alloantibodies → impacts plasma transfusions, thus only AB plasma can be safely transfused in cats
□ Additional naturally occurring alloantibodies may exist in plasma unit → consider crossmatching plasma
What precluded blood-typing, crossmatching, and Coomb’s testing?
o True (persistent) autoagglutination precludes blood-typing, crossmatching, and Coombs’ testing
What are the top breeds of cats that are Type B?
Devon Rex and exotics
What type of hypersensitvity reaction occurs with IMHA?
RBCs destroyed (type II hypersensitivity rxn) → extravascular or intravascular hemolysis
How does extravascular hemolysis occur in IMHA?
o Extravascular hemolysis: Ig or complement-coated RBCs removed by phagocytic cells (reticouloendothelial system/mononuclear phagocyte system)
How does intravascular hemolysis occur in IMHA?
RBCs coated with enough IgG or IgM to fix complement (10-20% of dogs)
What is the difference between primary and secondary IMHA, what is most common?
§ Primary IMHA: True autoimmune rxn against RBCs → 60% to 75% dogs (since no underlying etiology identified)
§ Secondary IMHA: RBCs destroyed as “innocent bystanders” of immune rxn against some foreign protein that may be adherent to RBC surface (most common form in cats)
o Trigger protein: Viral or bacterial infection, drug administration, or neoplastic processes
Name 4 causes of inherited causes of hemolytic anemia.
- Pyruvate kinase deficiency
- Phosphofructokinase deficiency
- Chrondrodysplasia/anemia
- Nonspeherocytic hemolytic anemia
Name 4 causes of IM (primary) hemolytic anemia.
- Primary (idiopathic) IMHA
- IMHA assoicated with SLE
- Neonatal isoerythrolysis
- Incompatible transfusion
Name 1 metabolic cause of hmeolytic anemia.
Hypophosphatemia
What 2 cancers are the most likely to result in hemolytic anemia?
Microangiopathic anemia associated with hemangiosarcoma and lymphoma
Name 8 causes of infectious hemolytic anemia?
- Babesia (canis and gibsoni)
- Mycoplasma (haemominutum, haemofelis, haemocanis)
- Dirofilaria immitis
- Bacterial endocarditis
- FeLV
- Leptospirosis
- Cytauxzoon felis
- Ehrlichia canis
Name 9 toxin or drug related causes of hemolytic anemias.
- Onion toxicity
- Zine toxicity
- Methylene Blue
- Copper toxicity
- Propylthiouracil
- Methimazole
- Sulfa drugs
- Penicillins and cephalosporins
- Quinidine
What is the signalment of IMHA in dogs?
Middle age (median 6-7 yrs) Females Any breed (overrepresented breeds: cocker spaniels, English springer spaniels, collies, poodles, Old English sheepdogs, and Irish setters)
Which breeds are over-represented in IMHA in dogs?
Overrepresented breeds: cocker spaniels, English springer spaniels, collies, poodles, Old English sheepdogs, and Irish setters