Collateral damage: “autoimmunity in

the battle against infection”

Dr Richard K. Burchell (B.Sc. (hons), B.V.Sc., MMedVet (SAM))

Senior Lecturer, Small Animal Medicine

Department of Companion Animal Clinical Studies

Faculty of Veterinary Science

University of Pretoria

The immune response

• Innate immune system

– Non specific (kills wide variety)

– Coded by genes

– Recognise PAMPs, DAMPs – Recognise PAMPs, DAMPs

• LPS, viral capsid, double stranded RNA

– Humoral

• Complement, acute phase proteins, ROS

– Cellular

• NKs, neuts, macrophages

• Specific immune response

– Specific – CDV, parvo, CAD, E.Coli

– T and B cells

– Not coded by genes – Shuffling of genes in every individual

The immune response

– Shuffling of genes in every individual

» Positive and negative selection

– Recognises antigens through a TCR

– Humoral

• Antibodies

– Cellular

• Cytotoxic T-Cells

Immune recognition

• Antigens are foreign molecules

• They are presented to the immune system

• Recognised by T cells (lymphocytes)

• T cells drive the immune response• T cells drive the immune response

– Antibodies

– Cell mediated attack

T cell’s – military intelligence

• T – cells develop in thymus (T)

• They have a unique TCR

• Created by gene shuffling

• Therefore TCR is not heritable (like shuffling cards) • Therefore TCR is not heritable (like shuffling cards)

• TCR’s can recognise virtually ANY antigen

» Self and non-self

• There are 2 major forms

– Helper T cells (Th)

– Killer T – cells (Tc)

T – Cells

• Helper cells drive the immune response

• Antibodies

• Cytotoxic response

• Response is driven against the pathogen • Response is driven against the pathogen

through unique TCR’s

• There are 2 major forms of Th cells

• Th 1 – cytotoxic reponse

• Th 2 – humoral (antibody) response

Innate

immune

response

Th Cell antigen recognitionTh Cell antigen recognition

Specific

immune

response

Immune recognition

• How does the T cell get to “see” the antigen? • Presented on cell surface many cells by 2 main

molecules (encoded by HLA gene)

– MHC I

• All nucleated cells• All nucleated cells

• Presents self and non-cell antigens

• Recognised by unique TCR

• The T cell has to carry CD8 (a killer T cell)

– MHC II

• Only professional APCs

• Only presented to T helper cells

• This sets up the immune response

T – cell recognition

• For Th to recognise antigen:

• The presenting cell must display the antigen to the

unique TCR

• The cell must display the antigen on MHC II

» This prevents T cells from driving an IR to antigens on the

surface of non-immunological cells

• For Tc to recognise an antigen

• It must be “armed” by a Th response first

• It recognises antigen on MHC I

The TCR – “a loaded gun”

• TCR’s to self antigens are a loaded gun

• How is autoimmunity prevented

– Through deletion of T cells during development

• Positive and negative • Positive and negative

– T Reg cells (later)

– Protected by lack of innate response

• Self antigens not recognised by innate IR

Inflammation and autoimmunity

• Collateral damage possible when targeting

antigens

• Immune response must attack pathogens but

avoid self antigens avoid self antigens

Excuse me Sir, but won’t we hit our own troops?

Yes… but we’ll hit theirs as well

Guiding the arrows – prevention of

autoimmunity

• T cell selection and deletion

– Deletes many T cell clones

• T regulatory cells

– Decrease the severity of T cell response – Decrease the severity of T cell response

• Immuno-privileged sites

– Brain, joints, eye

• Lack of innate response

– T cells respond to AG on APC’s

T cell differentiation

Driving autoimmunity

• Some antigens on pathogens resemble self

antigens – molecular mimicry

• PAMPs and DAMPs activating IR in presence of

self antigens self antigens

• Th17 bias?

Types of Autoimmunity

• Type I hypersensitivity

• Type II hypersensitivity

Types of Autoimmunity

• Type III hypersensitivity

Types of Autoimmunity

• Type IV hypersensitivity

Types of Autoimmunity

Autoimmune diseases

• Haematological• IMTP, IMHA (2)

• Neuromuscular/musculoskeletal• MG (2)

• GME • GME

• Polyarthritis (2 and 3)

• Rheumatoid arthritis

• Respiratory • Asthma (1)

• EB

• Urinary• Glomerulonephritis (3)

Immune Mediated Haemolytic

Anaemia

• Most common cause of anaemia in non-endemic babesia areas

• Immune mediated destruction of RBCs

• Severe anaemia• Severe anaemia

• Primary vs. Secondary

• Rx underlying cause (secondary)

• Immunosuppression

• Thromboembolic complications

IMHA

• Pathogenesis

– Antibodies directed against RBC receptors

– Agglutination/opsonisation erythrophagocytosis

– Activation of complement – rupture of RBCs – Activation of complement – rupture of RBCs

– Severe haemolysis

– Release of thromboplastin (activation of clotting

cascade)

– Massive release of inflammatory mediators

IMHA

• Primary– Idiopathic

– Abs against RBCs

– No underlying cause detected

• Secondary • Secondary – Infection

• Babesia, erlichia

– Drugs• Cephalosporins, penecillins

– Neoplasia• LSA

Clinical signs

• Anaemia

• Haemolytic serum

• Icterus

• Haematuria (Hgburia)• Haematuria (Hgburia)

• Exercise intolerance

• Tachycardia

• Acute onset dyspnoea (?)

• DIC

Diagnosis

• No one diagnostic test

• Combination of clinical findings

– Anaemia (PCV less than 20%)

• Regenerative (most cases)

– Inflammatory leukogram– Inflammatory leukogram

• Neutrophilia

– Spherocytosis (more than 30%)

– Coombs +ve

– ISA positive

Regenerative anaemia

• Absolute reticulocyte count

• > 60, 000/ul

• Red cell distribution width (RDW)

• >16% • >16%

IMHA – MDB

• Blood smear (babesia, erlichia) neutrophilia?

Spherocytosis?

• CBC/PCV BLSM/TSP

• ISA • ISA

• Faecal (hookworm)

• Urine (hgburia?)

In saline agglutination test

• Test principle

– Drop of blood with drop of saline

– Look for agglutination

– Macro or micro – Macro or micro

ISA

• RBCs can stick together

• Saline to wash apart

Regenerative anaemia

• Most dogs have regenerative anaemia

– If longer than 5 days

• Up to 10% may have non-regen anaemia

– PRCA, maturation arrest, hyperplastic bone – PRCA, maturation arrest, hyperplastic bone

marrow

Coomb’s test

• Detects Abs against IgG and Compl

• A few methods

• DAT

• Poor sensitivity • Poor sensitivity

– From 48% to 70% depending on technique

• Newer bedside techs compare well with gold

standard

IMHA - approach

• Anaemia

• ISA +ve –ve

• Leukocytosis

• Spherocytosis• Spherocytosis

• Coombs +ve -ve

IMHA approach

• Drug hx – sulphas? Cephalosporine

• Look for infec. Disease• Multiple Blsm

• Erlichia titres?

• PCR

• Urinalysis

• Heart scan?

• Look for neoplasia• Thoracic rads

• Abd US

IMHA approach

• If underlying cause not found

– You missed it

– This is a primary IMHA

DD’s for regenerative anaemia

• Blood loss (TSP helps) • Epistaxis?

• Haemoabdomen/haemothorax/haemarthrosis

• GI blood loss

• Blood loss in UT• Blood loss in UT

• Haemolysis/erythrophagocytosis• Babesia

• IMHA

• Toxic causes of haemolysis

• Hypersplenism

Immune mediated thrombocytopaenia

• Immune mediated destruction of platelets

• Also primary and secondary

– Erlichia, babesia, theileria? Anaplasma?

• Most don’t seem to bleed • Most don’t seem to bleed

• Platelet counts extremely low

• Rx with immunosuppression

Clinical signs

• Petechia, ecchymoses

• MM

• Ventral abdomen

• Hyphaema• Hyphaema

• Epistaxis

• Weakness, collapse

• Neuro sx?

• Many don’t bleed or have obvious Cx

Diagnosis

• Very low platelet count

– < 30 x 109/L

• Absence of other indications of low platelets

– Low WCC (BM issues) – Low WCC (BM issues)

– Acute bleed (?)

• Unlikely to be below 60-80

Diagnostic approach

• CBC – CONFIRM on blsm (clumping!)

– Other cell lines affected?

– Leukocytosis (inflammatory, e. canis?)

• UA, serum biochem• UA, serum biochem

– Organs affected?

• Infectious disease screen

– PCR, titres

• Imaging

– Thoracic rads and abd US

Some “pearls”

• IMHA is very inflammatory ITP is not

• ITP’s rarely bleed

– Hyperactive platelets?

– Increased plateletocrit? – Increased plateletocrit?

• An extremely low platelet count is indicative

of IM destruction

• Even if e.canis diagnosed, immunosuppression

will be required!