Immune mediated disease

• Types of immune-mediated disease

  Hypersensitivity disease:

  • Dermatological disorders; dietary intolerances; asthma (snake bites, bee stings).
  • Hypersensitivity reactions (usually T1, sometimes T4)

  Autoimmune disease:

  • Failure of self-tolerance (quite rare).
  • Influenced by; age, hormones, genetics, environment

  Immunodeficiency diseases/disorders:

  • Congenital - primary immunodeficiency
  • Acquired - failure of passive transfer, chronic infections e.g. FIV, inflammatory or neoplastic disease (drugs, malnutrition, toxins, stress which stop a normal immune response.
• Why does immune-immediate disease happen?

  Primary (idiopathic)

  • Caused by underlying dysfunction or imbalance in the immune system
  • Inappropriate response to self antigen.
  • Might need to exclude causes of secondary disease before having the confidence to treat.

  Secondary:

  • Triggers include:
  • Infection
  • Inflammatory disease
  • Drugs - e.g. TMPS
  • Neoplasia
• What is immunodeficiency?

  A functional problem with the immune system..

  Primary immunodeficiency - genetic; rare:

  • May affect e.g. neutrophils, lymphocytes, immunoglobulins.
  • Repeated infections in a young animal post-weaning or after loss of maternal antibody.
  • Pure bred puppy or several puppies from a litter experiencing problems.

  Secondary immunodeficiency - many causes; more common:

  • Immunosenescence
  • Medical immunosprresion (immunosuppresive drugs).
  • Specific infections e.g. FIV, parvovirus
  • Chronic disease.
• Haemolymphatic causes of immune mediated disease in dogs and cats

  IMHA

  IMTP

  Immune mediated neutropaenia (rare).
• Endocrine causes of immune mediated disease in dogs and cats

  Hypothyroidism

  Hypoadrenocorticism
• Cutaneous causes of immune mediated disease in dogs and cats

  Canine dermatomyositis

  Discoid lupus erythematosus (DLE)

  Pemphigus-pemphigoid complex.
• Musculoskeletal causes of immune mediated disease in dogs and cats

  Polyathritis (erolive and non-erosive)

  Myasthenia gravis (neuromuscular)

  • Focal vs generalised.

  Polymyositis/polyneuritis.
• CNS causes of immune mediated disease in dogs and cats

  MUO

  Granulomatous meningioencephalitis (GME)
• GI causes of immune mediated disease in dogs and cats


  Inflammatory bowel disease/ chronic enteropathy (IBD/CE).

  Pancreatitis in cocker spaniels

  • +/- other breeds.
• Renal causes of immune mediated disease in dogs and cats

  Glomerulonephropathies (many different types)
• Multi-systemic causes of immune mediated disease in dogs and cats

  Systemic lupus erythematosus (SLE).

  Many are poorly categorised but may see collections of clinical signs

  • Polyarthritis and meningitis
  • Pancreatitis and dry eye in cocker spaniels.
• Causes of IMHA and IMTP

  Some of the most common immune-mediated disease seen in small animal practices.

  RBC’s or platelets are destroyed due to a T2 (antibody-dependant cytotoxicity) mechanism: antibody binds to specific cell surface molecules.

  • Normal self antigen:
  • Primary immune system dysfunction and loss of tolerance.
  • Antigen exposed due to cell damage
  • Similiarity between self AG and foreign AG (e.g. infectious agent or drug).
  • Infectious agents bound to cell surface.
  • Non-biologic Ag bound to cell surface (e.g. drug toxin).
• Primary IMHA

  No known cause active trigger.

  Associaterd with an inherited predisposition in dogs;

  • Most commonly cocker spaniels, Springer spaniels and poodles.

  Aprroximate ly 65-70% of cases in dogs have primary (idiopathic) IMHA.

  
• Secondary IMHA

  The trigger or cause is an underlying condition, either recently or historically.

  Infection - e.g. Mycoplasm haemofelis, Babesia canis, FIP, FeLV, chronic bacterial.

  Neoplasia - e.g. splenic haemangiosarcoma.

  Drugs, toxins, vaccination - e.g. TMPS, methimazole

  Envenomation - snake bite, bee sting.
• IMHA in cats

  Is often secondary and can be triggered by:

  • FIP
  • Mycoplasma haemofelis
  • FeLV
  • Chronic bacterial infections

  
• What happens in IMHA - intravascular haemolysis

  Direct lysis of RBCs due to antibody binding and complement activation;

  • Implies a high concentration of antibody - more severe diseases?

  Less common than extra-vascular haemolysis but more acute.

  Release of free haemoglobin in to plasma;

  • Red/pink plasma +/- red/pink urine.
• What happens in IMHA - Extra vascular haemolysis

  Antibody binding to RBCs stimulates phagocytosis by mononuclear cells in the liver and spleen.

  Sperocytes are formed if partial phagocytosis occurs;

  • Useful marker for IMHA in a peripheral blood smear.

  Cats; phagocytosis can occur with;

  • Intracellular RBC parasites
  • Heinz bodies (oxidative damage).

  Haemoglobin metabolised by liver

  • Too much leads to jaundice.
• What do we see clinically in IMHA?

  Hepatomegaly

  Palle gums, pallor

  Jaundice

  
• Diagnosing IMHA - confirm the presence of anaemia

  PCV low, total solids usually normal - consistent with haemolysis

  • What colour is the plasma?

  Anaemia is usually moderate to marked (PCV/HCT <20%).
• Diagnosing IMHA - is the anaemia regenerative or non-regenerative?

  Degree of regeneration response depends on the magnitude of the anaemia

  • What are the features of regenerative anaemia - reticulocytes

  Could the anaemia be pre-regenerative if per-acute presentation

  • If it is acute (just happened) then reticulocytes may not yer be present in the blood.
• Diagnosing IMHA - what are the other cells lines doing?

  Neutrophilia is common with a shift towards immature cell lines

  • Bands, metamyelocytes.

  Are there enough platelets or could there be a combined IMHA and IMTP?

  • Mild thrombocytopenia is not uncommon and not significant.
• Diagnosing IMHA - look at a blood smear

  Are there any spherocytes? (hard to see in cats).

  Is there evidence of an inflammatory leucogram?

  Can you confirm an automated platelet count?

  Are there any abnormal cells suggesting myeloproliferative disease?

  
• Spherocytes in IMHA

  Small densely staining spherical RBCs, lack central pallor.\Small portions of the cell membrane may have been phagocytosed by mononuclear phagocytes; residual cellular tissue resumes the smallest shape possible - a sphere.

  Rarely recognised in cats since even normal RBCs have less central pallor than in dogs.

  • Presence implies that erythrocytes have surface bound antibodies or complement.
  • Indicator of IMHA in dogs.
  • Will be present in animals that have received transfusions - cells are damaged and foreign.

  
• What is the saline slide agglutination test?

  Testing for auto-agglutination.

  • Add 4 drops of saline to 1 drop of EDTA blood and mix by rocking the slide.
  • Look for evidence of macroscopic and microscopic agglutination

  
• What is Rouleaux?

  Clustering, sticky, piling of RBCs.

  • Normal finding in horses.
  • Indicates inflammation in small animals.
  • Related to increased stickiness of plasma with increased globulin content.

  
• Coombe’s testing

  What is the role of a direct Coombs test?

  • Identifies antibody on the surface of patient RBCs (therefore you must submit an EDTA sample).
  • More sensitive than an indirect Coombs reagent is used containing anti IgG, anti IgM and anti complement antibodies.
  • False +ve and false -ve tests occur.
  • Generally only worthwhile if the cases is challenging to diagnose:
  • No autoagglutination
  • No spherocytes
  • Non-regenerative anaemia.
• Biochemistry for IMHA

  What colour is the serum/plasma?

  • Orange/yellow - bilirubinaemia
  • Red = haemogloninaemia

  What might you expect to see?

  • Raised liver enzymes indicating hepatocellular damage (ALT) and resulting cholestasis (ALP) are common.
  • Associated with anaemia and hypoxic liver damage.
  • High bilirubin which with a low PCV/anaemia is consistent with pre-hepatic jaundice.

  Is there any evidence of an underlying disease that could be a trigger for IMHA?
• Urinalysis for IMHA

  Usually consistent with bilirubinuria or haemoglobinuria.

  Consider sediment analysis and culture in case UTI is a trigger IMHA.
• Ruling out possible trigger factors for IMHA

  Diagnostic imaging: is there an inflammatory focus or evidence of neoplasia?

  • Thoracic radiography
  • Abdominal radiography +/- ultrasound.
  • Ready to collect FNA from any suspicion lesions for cytology.

  Infectious diseases screen?

  • Mycoplasma haemofelis in cats?
  • Submit an EDTA sample for PCR
  • Is there a travel history?
  • Babesia in dogs?
• Treatment of IMHA

  Treatment of IMHA centres on two major focus points:

  1. Treat the underlying trigger/disease where possible
  2. Antibiotics
  3. Immunosuppresion
  4. Glucocorticoids;
  5. Azathioprine
  6. Mycophenolate Mofetil
  7. Cyclosporin
  8. Leflunomide
  9. Unfractioned heparin
  10. Oral anti platelet agents such as clopidogrel
• Primary IMTP

  An autoimmune disorder with production of antibodies directed against normal platelet antigens. This is usually IgG directed against surface glycoproteins.

  • Middle-aged female dogs, cocker spaniels, Old English sheepdogs, GSDs, and poodles.
• Secondary IMTP

  Antibodies target no self antigens absorbed onto the surface of platelets or when immune complexes become bound to platelet surfaces. Associated with;

  • Infection
  • Drug therapy
  • Neoplasia
  • Poly-immune syndromes
  • Vaccination as a cause of secondary IMT is possible.
• Clinical IMTP

  Often subclinical.

  Will present either of signs of concurrent anaemia or with bleeding once things are more severe.

  Bleeding with thrombocytopaenia is rare but can occur spontaneously when PLT <50,000L

  • Petechiae, ecchymoses, haematomas.
  • Epistaxis
  • Gingival bleeding.
  • Melaena/ haematochezia from bleeding into the GIT.
  • Haematuria from bleeding into the urinary tract.
  • Retinal haemorrhage, hyphaema, anterior uveitis.

  
• Laboratory findings of IMTP

  Low platelet count - automated or manual count. NB - check for clumping.

  In primary IMTP - biochemsitry profiles and coagulation tests are often normal.

  Haemotology - check for concurrent anaemia and/or concurrent cell line reductions which would indicate bone marrow disease.

  Infectious disease testing:

  • Ehrlichiosis, Rocky Mountain spotted fever, Anaplasmoasis, histoplasmosis, leishmaniasis, and distemper have been associated with secondary IMTP.
• Acute treatment of IMTP

  1. Transfusion

  2. Platelet transfusions

  3. Vincristine
• Transfusion

  Often not needed through bleeding risk increases <20,000/uL
• Platelet transfusions

  Available in USA, but variable response. Blood or platelet transfusions do not significantly raise the platelet count
• Vincristine

  Immunosuppressant activity, may induce thrombocytosis in 7 days
• Long-term treatment options for IMTP

  1. Immunosuppression

  2. Prednisolone

  3. Azathioprine

  4. Cyclosporine

  5. Mycophenolate Motefil

  6. Leflunomide
• Azathioprine

  Can take more than 4 weeks to become effective