Immune Mediated Disease

Question 1

Pathogenesis and Pathophys of erosive and non-erosive IMPA in dogs

Answer 1

Non-erosive - type 3 hypersensitivity -> complement activation, increased inflammatory mediators in synovium

Erosive - anti-collagen II Ab and type 4 hypersensitivity reaction on synovium (CMI). Th17 recruitment to synovium and development of pannus (fibrovascular tissue that p[roduces proteases)
May also have Ab targeted at other components of synovium

Question 2

Investigation for IMPA and justifcations/reasoning

Answer 2

CBC, Biochem
UA, UPCR, C+S (type 2 triggered by UTI)
Chest rads (type II triggered by respirato5ry infections)
+/- abdo u/s (type 4 triggered by neoplasia)
Joint fluid - >10% neuts, >5000 cell count
CRP - can be used for monitoring and differentiating IMPA from OA in dogs
Cervical spine imaging and CSF if concurrent neck pain - IMPA/SRMA combined dz
Check for sulfonamides (Dobermans especially)
Infectious dz testing (Rickettsial, Borrelia, Bartonella, Mycoplasma, Endocarditis)
ANA - if another immune mediated disease process present, to investigate for SLE whcih carries poorer prognosis.

Question 3

Recent Publications on canine IMPA

Answer 3

JSAP 2018 39 dog retrospective evaluation for correlation of IMPA with vaccination. No significant correlation but study may not have been large enough (OR 1.44 but wide 95% confidence interval)

JAAHA 2019 - 5 case description of IMPA with devedlopment of ligament laxity, theorised due to destruction of periarticular soft tissues.
Multiple disease relapses, poorly controlled by available immunosuppressives

JSAP 2022 - 73 case type I IMPA descriptive study.
95% ORR, 53% relapse, 63% complete cure. Half of dogs treated with pred alone needed 2nd immunosuppressive
19% death related to IMPA disease

Question 4

Evidence for Tx of canine non-erosive IMPA

Answer 4

Pred as first line Tx standard, but small studies have shown similar efficacy of cyclosporine, mycophenolate and leflunomide as sole treatments. Different side effect profiles and choice may be dictated by individual patient.

Half of dogs needed 2nd line treatment in recent JSAP study

As this is a type 3 hypersensitivity disease treatments that target CMI adn complement seem more likely to be efficacious

Question 5

Investigation/tests for erosive polyarthritis in dogs

Answer 5

Same as for IMPA but also:
Joint rads - takes a few months to see destruction but then see symmetrical subchondral bone lysis and alterations to joint space.
RF - rate of positivity reported is 30-70% depending on study.
ANA - recommended to screen for SLE
Synovial Bx - confirm diagnosis and r/o cancer.

Question 6

Pathogenesis of Feline nonerosive polyarthritis

Answer 6

MOST are infectious aetiology with direct infection of the synovium and secondary inflammation (though there is likely some type 3 hypersensitivity reaction in some diseases)
Known infectious causes include: Mycoplasma (felis, galeae); GIP, L-form bacteria (from cat bites, cause concurrrent cellulitis); Calicivirus (natural or vaccine); Streptococcal, Rickettsial.

For M. galeae disease may only be seen in immunocompromised cats that are infected.
For FCV vaccine induced disease it may be due to gain of virulence in vaccine or recent incubation of natural infection.

Question 7

Recommended investigation for feline non-erosive polyarthritis

Answer 7

CBC, Bio, UA, C+S, test for haematological infections and rickettsial dz depending on geographical location

Joint fluid should always be cultured and mycoplasma PCR performed. Sample >/=5 joints
Consider synovial bx for histo and culture (consider additional infectious dz testing on this though it has not been previously reported)
Oropharyngeal swab for FCV - may not be causative if positive and not always positive if the cause.

Question 8

Causes of feline erosive polyarthritis

Answer 8

Mycoplasma can cause erosive disease in some cats, as can some of the other infectious causes.
Also 2 distinct disease processes:
Feline periosteal proliferative polyarthritis - seen in young cats, progressive periosteal proliferation eventually causing ankylosis of the joints
May be improved with pred/2nd line drugs. Quite rare

Feline rheumatoid-like polyarthritis. Middle aged cats, Siamese may be overrepresented
Radiographs show severe subchondral central bone erosions. RF reported to be increased but cannot be measured commercially. Small treatment study reported response to combined methotrexate and leflunomide Tx.

Question 9

Treatment and recent publications for feline non-erosive polyarthritis

Answer 9

Start with doxycycline to cover rickettsial, L-form and Mycoplasma infections even if tests negative. Due to poor test specificity.
Should see quick response if infectious aetiology.

INI then consider immunosuppression (or trial fluoroquinolone treatment instead)

JFMS 2020 study reported 70% RR to immunosuppression in idiopathic disease, earlier studies reported only 50% response. but 8/11 cats needed 2nd line treatment (other cats had concurrent disease distant to the joint causing reactive polyarthritis).

Question 10

Pathogenesis and Pathophysiology of SLE

Answer 10

A combination of genetic mutations, environmental triggers and defects in B cell apoptosis result in T cell abnormalities including: reduced TCR signalling, decreased IL2 and T reg activation and increased IL 17 and IL6. The net result of which is increased B cell activity and autoreactive T cells.
There are multiple susceptibility and protective genes that have been identified including those involved with complement, APC; T cell signalling and B cell apoptosis

Once there is B cell hyperactivity there is generation of a large number of autoantibodies which result sin uncontrolled cytokine production and complement activation progressing to deficiency.
Antinuclear Ab (may be DnA or histones, combined with organ or tissue specific Ab. Causes IM damage via opszonisation or CD8 T cell apoptosis
B cell antibodies may cause type III immune reactions (polyarthritis, MPGN, vasculitis) or may be organ/tissue specific causing type II mediated disease (IMHA, IMT, dermatopathy, thyroiditis, myositis)

A single predisposing factor is not identified (though drugs and infections can cause SLE like syndromes). Though often affected patients are worsened by exposure to UV, as the damaged skin cells cannot undergo apoptosis and normal clearance (by macrophages or complement) so they become a source of antigenic stimulation for the disease.

Question 11

Diagnostic criteria for SLE

Answer 11

Positive ANA and 2 syndromes
Negative ANA and 3 syndromes

Syndromes include:
Polyarthritis
Oral ulcerations
Skin lesions consistent with immune mediated dermatopathy
Anaemia or thrombocytopaenia due to destruction
MPGN
Polymyositis
Neurological signs (seizures, CN deficits)
Serositis (effusion with no septic cause)

Question 12

Breeds overrepresented with SLE

Answer 12

GSD, Setters, Poodles, Collies

Question 13

Diagnosis for immun mediated neutropenia

Answer 13

Diagnosis of exclusion of other causes of neutropenia and demonstration of lack of improvement with time, then improves with steroids.

Think about infection, BM dz; inherited deficiency, low B12
DDx to exclude: rickettsial disease, BM injury (reversible); sequestration/septic focus, Grey collie cyclic haematopoiesis; border collie trapped neutrophil syndrome, B12 deficiency

Perform full baseline bloods, UA and rickettsial disease testing. imaging to look for infectious focus.
BM< will show myeloid hyperplasia, orderly maturation, incrreased M:E, peripheral cytopaenia and no bands.

Question 14

Pathogenesis and causes of immune mediated vasculidities

Answer 14

Pathogenesis poorly understood but likely a combination of type II and III immune mediated reactions
May be direct IM damage of vascular cells vs immune complex deposition in capillaries.

Possible causes are many but main exclusions are looking for systemic disease as this is a reaction not a primary disease process (though in some cases a trigger is not found).
DDx: ionfection, sepsis, DIC, rickettsial diseases, cold agglutinin (fibrinogen or globulin mediated); drug/food reaction; SLE

Question 15

Treatment options for cutaneous vasculidities

Answer 15

First of all treat/remove the trigger - in many cases this may result in resolution without any direct treatment of cutaneous lesions.

If there is no trigger or ddz is progressing rapidly anti-inflammatory to immunosuppressive doses of pred can be used (NB these may delay healing of any erosions).
Additional treatments include pentoxifylline, cyclosporine, tetracyclines or niacinamide

Question 16

Recent publications about sterile lymphadenitis

Answer 16

Both JSAP 2019
1 - English Springer Spaniels only (64 case descriptive study) - many had other cutaneous lesions and systemic signs of illness. Treatment response reported for 38 cases, 34 were pred alone and had good to excellent response. 8 required a seocond immunosuppressive medication
5 died/euth due to poor response

2 - Series of 49 cases of steroid responsive lymphadenitis, 16 were ESSp which were an overrepresented breed. 97% responded to treatment with pred, 18 relapsed (13 were ESSp.
4 dogs had other immune mediated disease at same time.

ESSp breed is overrepresented but not only breed affected, all dogs had some degree of lymph neutrophilic/macrophagic inflammation in nodes with or without necrosis.

Question 17

What is the mechanism of ITP

Answer 17

IgG autoantibodies binding to the GIIbIIIa receptor (fibrinogen) on platelets -> unable to aggregate with fibrin. Also affects megakaryocytes
The Ab designate the platelet for removal by macrophages (RES) in the liver and/or may enhance desialyation in the liver (causing early platelet dysfunction)

Question 18

JVIM 2020 study of anti-platelet Ab detection and dynamics found??

Answer 18

Used flow cytometry:
20% of secondary/non-ITP dogs had APA
All primary ITP dogs were positive.
Contrasts previous studies where some dogs with primary ITP were negative. So use as a rule out test may be useful.

Also reported that persistence of APA was not associated with response to treatment but that recurrence of APA after resolution was correlated with relapse. So Flow Cytom may be useful monitoring tool
HOWEVER relapse only occurred in 2 of 22 monitored dogs.
Unclear how long it takes for dogs to become negative for APA

Question 19

What did the JSAP ITP long term outcome study find

Answer 19

45 dogs monitored for >12months
90% survived to discharge; 31% relapse.
50% relapsed more than once
Relapsing group had longer time to platelet recovery.
As majority came off medication and did not relapse there is not indication for long term therapy - though those that do relapse have a high chance of doing so again
1 year mortality caused by ITP was 11.9% so not much more than hospitalisation

Question 20

How does the DOGiBAT score work

Answer 20

Validation study in JVIM 2018 - scoring of 9 anatomic sites as 0-2 for presence of bleeding.
Thus total score out of 18

Higher scores were correlated with need for transfusion and hospital stay duration
Further study to determine use in monitoring

Question 21

What is the evidence for current ITP treatment recommendations

Answer 21

• majority respond to pred without any adjunctive treatment.
• Small studies have demonstrated efficacy of MM as a single agent in ITP but it is slower onset
• no comparative prospective studies to determine superiority of one treatment over another.

A study of plt number and function after Vinc showed more rapid increase compared to pred alone and platelet function measured by P-selectin expression was not affected
Though another study reported development of neutropaenia after Vinc correlated with longer hosp stay - though was sstrongly correlated with concurrent cyclosporine administration

Minimal use for platelet transfusion because of their short half life and thus only short effect on haemostasis but could be used in life threatening scenario. RBC transfusion or whole blood best if haemorrhage induced anaemia/hypovolaemia
- recent study of lyophilised platelets compared to cryopreserved platelets found them to be non- inferior using DOGiBAT bleeding score (and is logistically superior for storage)

Small study of TPE in 4 ITP dogs unresponsive to conventional Tx - there was improved plt count in treated dogs though 1 was euthanised because of persistent bleeding after 3 treatments.

Question 22

DDx for thrombocytopenia

Answer 22

ITP - if severe
Secondary:
Infectious: Babesia, Ehrlichia, Anaplasma, Leishmania, FeLV
Neoplasia - lymphoma, HSA, Histiocytic sarcoma - others have lower levels of evidence.
Causes of inflammation - low LoE
Drugs - sulfonamides and cephalosporins

Question 23

Causes of IMHA and classes

Answer 23

Epitope unmasking - damage to tissue or cells resulting in exposure of previously cryptic antigen.
Molecular mimicry - drug or infectious epitope similar to self
Haptenization - reaction of an antigen with a carrier protein generating a new epitope and immune response
Superantigens - a class of immunostimulatory molecules produced by bacteria and viruses. Have potent immune effects due to their ability to bind to the MHC outside the antigen-binding cleft and to stimulate T cells in a T-cell receptor (TCR)-specific manner.

Class I = IgG and IgM agglutinate RBCs and opsonise
Class II = IgM activates complement -> intra/extravascular haemolysis
Class III - IgG mediated opsonisation but NOT complement or agglutination.

Class IV - IgM binding at low temps, causing tissue necrosis +/- anaemia
Class V - IgM binding at <4C

Question 24

What does carboxyhaemoglobin measure/what are its uses/recent publications

Answer 24

Carboxyhemoglobin (COHb) is a stable complex of carbon monoxide (CO) and haemoglobin and serves as a useful biomarker of blood CO concentration. Endogenous CO production also occurs under physiological and pathological conditions because of metabolism of heme-containing proteins, most notably of Hgb

Metabolism of Hgb and increased inflammatory cytokines in IMHA should both cause increase in CO-Hgb

JVIM 2022 study found significant difference between dogs with haemolytic and non-haemolytic anaemia
Be4st Sens/Spec combo was 96 and 96% can get 100% of either without misclassification with slight adjustment to reference. ALL WERE TRANSFUSION NAIVE!!
Not assessed in PIMA or with other inflammatory diseases
Differential diagnoses for elevated COHb other than hemolysis and CO intoxication are myriad, and include internal bleeding, exposure to drugs, sepsis,hepatic and respiratory diseases, and various additional inflammatory diseases

Question 25

Pathophys of Shar Pei Fever

Answer 25

Excessive production of hyaluronic acid due to genetic mutation –> excessive breakdown products which are proinflammatory –> IL1 and 6 release which cause systemic inflammation

Amyloidosis occurs due to abnormal breakdown products of SAA accumulating in tissues. SP are affected at a younger age compared to other breeds but less often have nephrotic syndrome. In Shar-Pei this tends to occur in renal medulla (not cortex) hence less severe proteinuria, amyloid also accumulates in liver

Question 26

What causes amyloidosis

Answer 26

A breakdown product of SAA (an acute phase protein)
Chronic inflammation results in large amounts of this protein being generated and deposited in the kidney, spleen and liver. Though pathogenesis of this occurring is extremely variable. increased SAA is not sufficient for the deposition of amyloid leading to amyloidosis. The SAA deposition in AA-amyloidosis would be due to defect in the degrading monocyte-derived enzymes or genetically determined structural abnormality in SAA molecule

Renal deposits are primarily in the glomerulus for most breeds (causing a PLN and nephrotic syndrome) but in the Shar Pei and cats it occurs in the medulla so less severe proteinuria is seen.

A familial amyloidosis is also reported in Abyssinians

Question 27

Outline pathogenesis and pathophysiology of SIRS/sepsis: vascular, immune, organ and coag effects

Answer 27

Strong proinflammatory stimulus from PAMPs (LPS, peptidoglycan) and/or DAMPs (HMBGP1, DNA, Histones) bind to TLRs, NODs, Lectins of innate immune cells (dendritic, neuts, macros, NK cells)
-> upregulation of intracellular signalling pathways culminating in NFkB signal transduction to upregulate proinflammatory gene transcription.
In particular: IL1, IL6, TNFa, IL17
This triggers the hyperinflammatory phase of sepsis/SIRS:
- Vascular effects: enhanced adhesion for leukocytes, increased chemotaxis signals, enhanced platelet adhesion and secondary coagulation cascade through vWF and TF expression and release; production of vasodilatory substances (NO) and reduced responsiveness to vasoconstrictive signals; increased permeability to allow leukocyte migration. Clinical manifestation of hypotension and oedema
- Immune effects: Enhanced APC activation of adaptive response in particular Th17, NK cells and Th1 through IL17 and IL2. Ongoing recruitment/activation of innate inflammatory cells. Altered thermoregulation due to cytokine storm. After excessive activation there is a shift to IL 10 production and Treg promotion (hypoinflammatory phase) with lymphocyte apoptosis predominating and an immune paralysis increasing susceptibility to new/pre-existing infections.
- Organ effects: circulatory dysfunction and microcirculatory changes -> tissue hypoxia and subsequent ischaemia induced apoptosis. There is also ROS induced mitochondrial damage that causes dysfunction and cytopathic hypoxia (mismatch of O2 delivery to utilisation). Precipitating dysfunction of several organs potentially ((MODS)
- Coagulation effects: increased TF and vWf expression due to inflammatory cytokines, increased platelet activation, thrombin overactivation and pro-inflammatory feedback. Intravascular TF-F7a microparticles in circulation -> microthrombosis.
Depletion/reduced production of antithrombin, Protein C and TFPI, also reduced responsiveness to these factors.

Question 28

SIRS criteria

Answer 28

Temp none for cat; <37.7/>39.7C for dog
HR dog >160; cat <140/>225
RR >40
WBCC <5; >19.5, >5% bands

Question 29

Proposed theories for CIRCI and how to diagnose

Answer 29

Normal or elevated cortisol (as expected with inflammatory stimulus) but reduced/blunted response of body systems. May be due to inflammatory suppression of CRH and ACTH actions, or induced dysfunction of corticosteroid receptors or tissue resistance to effects of cortisol.
Also reduced binding to transcortin in blood may affect ability to enter cells

In people main diagnostic criteria is lack of response to vasopressors. No consensus on the identification in animals, nor RR for ACTH or cortisol in critically ill.
Pressor responsiveness is independent of ACTHST result

Consider hydrocortisone CRI if no response to IVFT adn vasopressor therapy.

Question 30

Treatment of SIRS/Sepsis

Answer 30

Control of infectious/inflammatory disease
Early goal directed therapy -> maintaining tissue perfusion.
If hypotension not responsive to IVFT and no longer considered hypovolaemic then consider Dobutamine (B1 agonist, minimal vasoconstrictive effects, predominantly ionotropic)

If still no response then vasopressor therapy (adrenalin, vasopressin, dopamine) - these cause peripheral vasoconstriction so may interfere with tissue perfusion and as such cause MODS. If still no response a hydrocortisone CRI may be indicated for CIRCI - though dosage recommendations are lacking

Avoid hypo/hyperglycaemia
FFP - limited evidence as difficult to determine where on coagulation/DIC spectrum a patient is. But AT and protein C content may be beneficial.

Question 31

Pathogenesis of SRMA (acute and chronic)

Answer 31

Not well understood
Presumed IMD due to response to steorids and lack of other cause
Likely Th2 mediated autoimmunity with excessive production of IgA well documented (though not sure how this manifests as disease)
There is increased expression of leukocyte adhesion molecules increasing their migration into the CSF as well as increased MMP disrupting the BBB.

In acute disease this causes leptomeningeal inflammation and inflammation of associated arteries.
With chronicity this develops into fibrosis of the leptomeninges and arteries with LP infiltration and immune mediated vasculitis causing ischaemia, necrosis and sometimes haemorrhage.

Question 32

Evidence for Biomarkers in SRMA

Answer 32

2021 Vet J biomarker review - CRP and SAA are APPs that have good correlation with disease response to treatment and relapse and can serve as surrogate markers in monitoring but are not useful as a sole diagnostic test. However note that these are increased in SRMA but not in MUE similar to other inflammatory markers.

IgA in the serum and CSF increase with SRMA and a 2015 study comparing serum and CSF levels to other brain diseases found increase was strongly assoc with SRMA (but also other inflammatory brain disease).
Combined Serum and CSF levels were significantly higher in SRMA compared to other inflammatory brain disease though.
Combined Sensitivity of 91% and specificity of 78%

CSF HSP, CD11a expression and cytokines are still being investigated

Question 33

Evidence for treatments in SRMA

Answer 33

Early reports demonstrated good steroid response - duh, though given predilection for large breeds there was a high risk of assoc AEs.

A retrospective uncontrolled study in JAAHA 2020 reported good response and 81% complete remission at 2y in 26 dogs Tx with a 3 month protocol of tapering pred combined with aza (SID for 1 month then EOD for 2 months).
Prospective comparative trials of different meds are lacking

A JVIM 2019 paper, retrospective series of 46 dogs reported a higher relapse rate of 48%. Though treatments were variable, and difficult to draw direct comparison b/w them