Small Animal Medicine - Immune Mediated

Self-recognising T cells deleted during thymic development

Only armed T cells mount an immune response

T reg cells and immune tolerance

What prevents autoimmunity?

During thymic development - T cells selected for recognition of MHC I and MHC II

+ve selection - Th and Tc cells

-ve selection - delete self-recognising t cell receptor bearing cells. This process is not perfect, most dogs/cats retain self-recognising t cells

Thymic development

Only mounted if innate immune system presents antigen to T cell (MHC II): Professional antigen presenting cells (APCs)

When is the T cell response mounted?

Through Toll-like and NOD receptors

How does antigen presenting cells recognise PAMPS

Type 1 - IgE antibodies, mast cell degranulation - histamine, serotonin and heparin release. Anaphylaxis

Type 2 - (cytotoxic) antibodies directed towards a self antigen - inhibition of antigen & inflammation - IMHA, myasthenia gravis

Type 3 - (immune complexes) antigen/antibody complexes accumulate in tissues & activate inflammation - SLE, IMPA

Type 4 (delayed type) - armed Tc cells cause tissue destruction & accumulation of macrophages & lymphocytes Thyroiditis

Outline the immune mediated disease mechanisms

Immune mediated haemolytic anaemia

Immune mediated thrombocytopenia

Immune mediated polyarthritis

Meningitis in dogs

What are the common immune mediated diseases?

Glucocorticoids - mainstay of therapy

Binds to genomic and non-genomic receptors

Increase glucose production, fat synthesis, muscle breakdown

Increase urine production/water intake

Immunosuppression therapy

Wide number of effects, main effect is to reduce expression or increase expression of many proteins

What is the main effect of Immunosuppression therapy

PU/PD, polyphagia, muscle wastage, panting, pot belly, hair loss, GI side effects (GI ulcers)

What are the side effects of Immunosuppression therapy

Start high and taper

2mg/kg - 7-10 days, slow taper

Tapering to prevent iatrogenic hypoadrenocorticism

Not necessary if it's a short course (

Outline the dosage regime for immunosuppression therapy

Short acting: Hydrocortisone, cortisone acetate

Immediate acting: Prednisone, prednisolone, methylprednisolone

Long acting: Dexmethasone

What are some types of glucocorticoids for immunosuppression therapy

Purine analogue: Competes with purines for synthesis of nucleic acid

Thiopurine methyl transferase (TPMT) is an important enzyme preventing toxicity - deficient in some dogs & often in cats

Used as second line immunosuppressive for many years, evidence is weak.

Outline the use of Azathioprine for immunosuppression therapy

Binds to cyclophilin A and inhibits calcineurin

This step is needed for Il2 Th activation

Very targeted inhibition of the immune system

Used as second line immunosuppressive

Outline the use of Cyclosporine for immunosuppression therapy

Common GI side effects, Liver injury in rare cases

What are the side effects of Cyclosporine

Inhibits purine synthesis

Has become a common second line immunosuppressive

Little evidence to support efficacy

Outline the use of Mycophenolate mofetil for immunosuppression therapy

GI and cytopenias

What are the side effects of Mycophenolate mofetil

Chlorambucil

Cyclophosphamide

What are some chemotherapeutic agents for immunosuppression therapy

Immune mediated haemolytic anaemia (IMHA)

What is the most common cause of anaemia in non-endemic babesia areas

Antibodies directed against RBC receptors

Agglutination/ opsonisation erythrophagocytosis

Activation of complement - rupture of RBCs

Severe haemolysis

Release of thromboplastins (activation of clotting cascade)

Massive release of inflammatory mediators

Outline the pathogenesis of Immune mediated haemolytic anaemia (IMHA)

Idiopathic

Abs against RBCs

No underlying cause detected

What can cause primary IMHA?

Infection (babesia, erlichia)

Drugs (cephalosporins, penicillins, TMS)

Neoplasia

What can cause secondary IMHA?

Anaemia

Haemolytic serum

Icterus

Haematuria

Exercise intolerance

Tachycardia

Acute onset dyspnoea

DIC

What are the clinical signs of IMHA?

Blood smear -> neutrophilia, spherocytosis?

CBC/ PCV BLSM/TSP

ISA

Faecal (hookworm)

Urine (haemoglobinuria)

What is the minimum data base for diagnosing IMHA?

Regenerative Anaemia (PCV

How can you diagnose IMHA?

Drop of blood with drop of saline

Look for agglutination -> won't wash apart if IMHA because stuck together with antibodies

How can you do a agglutination test for IMHA?

Blood loss: Epistaxis, haemoabdomen/haemothorax/haemarthrosis, GI blood loss, blood loss in UT

Haemolysis/erythrophagocytosis: IMHA, toxic causes of haemolysis, hypersplenism, PFK & PK deficiencies (rare, puppies)

What are some differentials for IMHA?

Restore HCT, immunosuppression, prevent complications (Thromboembolism, DIC, SIRS)

What are your goals in treating IMHA?

Cornerstones: Blood transfusion, immunosuppression, thrombo-prophylaxis

TX underlying DZ

Fluids - crystalloids (electrolytes, perfusion) blood

Omeprazole/ranitidineandulsanic

Cerenia/metoclopramide

How can you treat IMHA?

Life saving, given according to CS -> HR, HCT below 15 in dogs and 12 in cats

Packed cells most ideal

Outline the use of a blood transfusion when treating IMHA

Glucocorticoids

Azothiaprine

Cyclosporine

Cyclophosphamide, no evidence supporting benefit

What can you give for immunosuppression when treating IMHA?

Prednisolone, dexamethasone

Decrease PG synthesis -> very potent anti inflammatories

Decrease T cell response

Treat 7-10d (hopefully HCT increase by then) then taper

Outline the use of Glucocorticoids when treating IMHA

PU/PD, weight gain, muscle wastage, Cushing's syndrome

What are the side effects of Glucocorticoids when treating IMHA

Disrupts DNA synthesis, studies showing no benefit over GC

2mg/kg OID 30 days, then EOD

Outline the use of Azothiaprine when treating IMHA

Well tolerated

Low SE profile

BM suppression

Hepatotoxicity

What are the side effects of Azothiaprine when treating IMHA

Second line (5-10mg/kg/d)

Calcineurin antagonist

Targeted Th therapy

Prevents activation of T cells

5 to 10mg/kg/day

Outline the use of Cyclosporine when treating IMHA

Options: ULDA, Clopidogrel, LMW heparin, adjusted HMW heparin, Dabigatran, Warfarin

Thrombosis: Clopidogrel, adjusted heparin

What are the options of thromboprophylaxis when treating IMHA?

Look at HCT daily -> safe to discharge once above 30

Then every 3d for 10d

Then every week, then bi-weekly (stop after 3 months)

What monitoring should be done when treating IMHA?

Antibodies are directed against platelet surface receptors: GpIIb/IIa

Platelets are removed from circulation -> disrupts primary clotting - clot initiation

Causes bleeding, petechiae: Epistaxis, melena, bleeding into body cavity

Outline the pathogenesis for immune mediated thrombocytopenia (IMT)

No underlying cause

Primary is rare in cats

What are the causes of primary IMT?

Infection, erlichia, babesia, anaplasma, lepto

Neoplasia

Drug exposure - penicillins, sulphonamides

Vaccines

Dirofilarial/ parasites

What are the causes of secondary IMT in dogs?

FeLV, FIV, FIP, lymphoma

What are the causes of secondary IMT in cats?

Subclinical -> non specific CS

Signs of haemorrhage -> petechiae, ecchymoses, hyphaema, melena, haematuria, pallour

Tachycardia -> if severe

Collapse and weakness in severe cases

What are the clinical signs of IMT?

PCV, TP, Blood smear

CBC

Serum biochem

Infectious DX screening -> erlichia, lepto, babesia, bartonella

Body cavity imaging: Rads, U/S, CT chest abdomen

Rule out bone marrow DZ -> Biopsy

How can you diagnose IMT?

PCV, TP, Blood smear -> You'll see thrombocytopenia 1-2 /HPF (8-10 per HPF is normal), anaemia

CBC: Low platelet count

What is the minimum database for diagnosing IMT?

Consumption sequestration from cancer -> but shouldn't be this low

Blood loss, consumption

DIC

Macrothrombocytopenia

What are some differentials for IMT?

Restore platelet count

TX underlying cause

TX anaemia

Symptomatic & supportive as needed

What are the goals when treating IMT?

Anaemia, tachycardia, severe thrombocytopenia

Collapse, weakness, PCV

When is hospitalisation needed in cases of IMT?

Immunosuppression

Vincristine in severe thrombocytopenia's -> when seeing bleeding

Supportive care

Human IV immunoglobulins (Been shown to increase platelet counts)

How can you treat IMT?

Prednisolone (2mg/kg) until platelet count normalises - begin taper

Second line not recommended unless refractory or relapsing: Mycophenalate,cyclosporine

Outline what can be used for immunosuppression when treating IMT

Be careful with crystalloids -> If dehydrated, V+

Fresh whole blood if anaemic

Plasma rich platelets

Antiemetics

Abs if infection present

What supportive care should be done when treating IMT?

Generally good (80-90% dogs achieve remission)

What is the prognosis for IMT?

Concurrent ITP and IMHA

Dogs with IMHA and platelet counts

What is "evans" syndrome?

Similar to IMHA/ITP

Vincristine could be considered in life-threatening thrombocytopenia

How can you treat "evans" syndrome?

Most common type is Type 3 hypersensitivity - ag/ab complexes causing inflammation in joints

Divided into erosive and non erosive

Primary (idiopathic) or secondary (infection, inflammation, cancer)

Outline the pathogenesis for immune mediated polyarthritis

Fever, shifting lameness, joint swelling, joint heat/pain, "fever of unknown origin"

What are the clinical signs of immune mediated polyarthritis

Arthrocentesis

Cytology of the joint

Rule out infectious DZ

How can you diagnose immune mediated polyarthritis

Sterile prep of joints

Collect from small joints: Collect from carpi & tarsi, collect from more than one joint

Outline the use of Arthrocentesis when diagnosing immune mediated polyarthritis

Usually contained non-degenerative neutrophils

Avoid blood contamination

Consider sample for culture if suspect septic

Outline the use of cytology of joint when diagnosing immune mediated polyarthritis

Corticosteroids (2mg/kg) until signs resolve, then start to taper, use CRP to help with decision making

Additional immunosuppressives: Mycophenalate, cyclosporine, leflunomide

How can you treat immune mediated polyarthritis

Most dogs achieve remission (+/-70-80%), some require life-long medication

What is the prognosis for immune mediated polyarthritis

Mycoplasma gatae

What is a differential diagnosis for immune mediated polyarthritis in cats?

Systemic type 3HS

Skin, joints, kidneys

Fever, anaemia

Anti-nuclear and anti-cytoplasmic antibodies

Most non-erosive arthritis

Systemic lupus erythematosus

Vitamin P -> Corticosteroids

Combine immunosuppressives -> esp in cats

Might need to mange proteinuria

How can you treat Systemic lupus erythematosus?

Antibody destruction of neutrophils

Severe deficiency of neutrophils

What is immune mediated neutropenia?

Non specific signs -> lethargy, anorexia, fever

Blood smear -> severe neutropenia

Fever might be present

What is the presentation of immune mediated neutropenia?

Consumptive -> pyometra, pyothorax

Infectious dx -> parvo, erlichiosis

Drug associated -> chemo, TMS, azothiaprine

Bone marrow suppression -> aplastic anaemia, erlichia, myelodysplasia

Immune mediated -> abs destroy neutrophil precursors

What are the possible causes of immune mediated neutropenia?

CBC, biochem, UA

Infectious DX screening

Body cavity imaging

Bone marrow aspirate

How can you diagnose immune mediated neutropenia?

Corticosteroids: TX until neutrophil count has recovered, then taper

90% response rate

How can you treat immune mediated neutropenia?

Suspected immune mediated pancytopenia

TX: Prednisolone, cyclosporine

6 mo F Cocker Spaniel presented for non-regen anaemia

HX of lethargy inappetence

UTD all preventatives

PCV 25%

Blsm, no reticulocytes, severe leukopenia, severe thrombocytopenia

E.canis - negative

Thoracic rads, abdo US negative

No known exposure to drugs, toxins

What is your diagnosis and how can you treat?

Non specific -> lethargy, anorexia, weakness

Anaemia

Bleeding/ bruising

Infection

What are the signs of immune mediated pancytopenia?

Infection -> erlichia, distemper, FeLV

Drugs/toxins -> chemo

Bone marrow cancer -> lymphoma, MM

What are the causes of immune mediated pancytopenia?

Rule out infectious causes: Testing as per geographical region

CBC, biochem, U/S, body cavity image

Bone marrow biopsy/aspirate

How can you diagnose immune mediated pancytopenia?

Corticosteroids, second lime immunosuppressives, blood if needed, Abs to prevent secondary infections

How can you treat immune mediated pancytopenia?

Previously known as non-reg IMHA

Moderate to severe non-regenerative anaemia

Spherocytosis less common

Only 30% have leukocytosis

Still have increased risk of thromboembolism

What is precursor targeted immune mediated anaemia (PIMA)?

Non-regenerative anaemia

Consider: Imaging (abdominal U/S), rectal to check for blood, CT, endoscopy

How can you diagnose PIMA?

Chronic blood loss - iron deficiency

What is a differential diagnosis for PIMA?

Similar to IMHA: Immunosuppression, thromboprophylaxis

How can you treat PIMA?

Failure of immune system

Susceptibility to infection (normal environmental pathogens)

Failure to acquire or sustain immunity

What is an immune deficiency disorder?

Physical barrier (mucus, cilia, skin)

Antibodies (IgA)

Acid/noxious chemicals (stomach)

Barrier/mucosal immunity

Non-specific

Humoral (proteins, acute phase proteins, proteases, iron scavenging) Complement activation.

Cells - neutrophils, macrophages, eosinophils, basophils, natural killer cells

Innate Immune system

Antigen specific

Humoral - antibodies (IgG, IgM, IgA)

Cells - cytotoxic T cells (CD8 bearing)

Specific or adaptive or "programmable" Immune system

Genetic

What can cause a primary immune deficiency?

Immune mediated, Infectious, neoplastic (bone marrow DZ)

What can cause a secondary immune deficiency?

Granulocytes have nuclei that are not lobed (segmented)

Most dogs are normal -> some reduced neutrophil function

Misinterpreted as left shift

Pelger-Huett anomaly

Affects Australian Shepherds + Cocker spaniels

What breeds are affected from Pelger-Huett anomaly

Integrin - Mac 1 def. Protein responsible for neutrophil docking for extravasation

Have very high leukocyte counts (neuts mainly)

Fever, decreased healing, susceptibility to infection

Canine Leukocyte Adhesion Deficiency

Irish setters

What breeds are affected from canine leukocyte adhesion deficiency?

Cycles of neutropenia every 11-12 days, followed by recovery

Susceptible to infection during this time

Mutation APb31 gene - neutrophil elastase deficiency (release from BM)

Can also affect platelets - bleeding

Canine cyclic neutropenia

Gray collies (colour dilution of border collies)

What breeds are affected from canine cyclic neutropenia?

X-linked version Welsh Corgi's

B and T cell deficiency

Stunted growth

Don't survive to adulthood

Severe combined immunodeficiency (SCID)

Immune mediated neutropenia

Immune mediated or primary pancytopenia

What are the acquired immune deficiency diseases?

Organism infects white cells/ platelets

Can cause fever, LN enlargement, thrombocytopenia

BM suppression in chronic cases

What can Erlichia canis cause?

Brown dog tick is vector (Rhipicephalus sanginus)

What is the vector for Erlichia canis

Feline panleukopenia

Canine parvovirus

Canine distemper

Feline leukemia virus

What viral diseases can suppress bone marrow?

Congenital -> too few nicotinic receptors (acetylcholine receptor)

Acquired -> antibodies directed to acetylcholine receptors

What can cause Myasthenia gravis

Weakness/ fatigue (gait becomes stiff, collapse) -> after exercise

Dysphagia/ regurgitation (oesophageal involvement): Megaesophagus, aspiration pneumonia

What are the clinical signs of myasthenia gravis

CS

Edrophonium response test (not very reliable)

Acetylcholine receptor antibody (expensive)

How can you diagnose myasthenia gravis

Pyridostigmine (acetylcholine esterase inhibitor) - longer acting - put them on this to improve their strength

Corticosteriods -> more controversial, not a lot of evidence that they work

How can you treat myasthenia gravis

Stiff gait -> similar to MG (myasthenia gravis) - tend to be stiff from rest (whereas MG is stiff after exercise)

Short stilted gait

Muscle atrophy

Might have oesophageal involvement

Breed specific variations: Boxer poor, Viszla good

What is the presentation for immune mediated polymyositis?

CBC, biochem, UA

CK might be elevated (not always)

Consider toxoplasma/neospora testing

Consider MG testing

Muscle biopsies

How can you diagnose immune mediated polymyositis?