Path2220 INTRODUCTION TO HUMAN DISEASE

AUTOIMMUNITY

Dr. Erika BosioResearch Fellow – Centre for Clinical Research in

Emergency Medicine,

Harry Perkins Institute of Medical Research

University of Western Australia

erika.bosio@uwa.edu.auPATH2220

2017

OBJECTIVES

Aims of this lecture:

– To illustrate the spectrum of autoimmune diseases

– To define pathogenic aspects of autoimmunediseases

– To use SLE as model a model of systemic autoimmunity

– To use thyroid disease as a model of organ-specific autoimmunity

What is Autoimmunity?

Autoimmunity – presence of auto-antibodies and/or

self-reactive T cell responses. Only when these

responses cause clinical abnormality is an

autoimmune disease present.

Hashimoto’s ThyroiditisSystemic Lupus Erythematosus

(SLE)

ACTIVATION OF T AND B CELL RESPONSES

T- AND B-CELL

INTERACTION

How does the body control self-reactivity?

IMMUNOLOGICAL

TOLERANCE

Lack of response of T- or B-cells to antigen

exposure:

•Central and peripheral tolerance

•Principal mechanisms

Clonal deletion of self reactive lymphocytes

Tolerance due to clonal anergy

Tolerance caused by lack of communication

Suppression of self-responses

IMMUNOLOGICAL

TOLERANCECentral (Intrathymic) Mechanisms of Tolerance :

Immature T-cells migrate from bone marrow to thymus

Interact with self peptide-MHC complexes on thymic epithelium

Double positive (CD4+/CD8+) thymocytes develop T-cell receptors (TCRs) – Only those with low affinity for self-antigens persist (Positive Selection)

Cells with dysfunctional TCRs or with very high or no affinity for MHC-self peptide complex undergo apoptosis (Negative Selection)

Positively selected cells then lose either CD4 or CD8 and leavethymus to function in periphery as mature CD4+ or CD8+ T-cells

Adapted from Walker, LSK, Abbas, AK [2002] Nat. Rev. Immunol. 2:11

IMMUNOLOGICAL

TOLERANCE

Peripheral (Non-thymic) Mechanisms of

Tolerance : • Peripheral T cell tolerance can be regulated by antigen

presenting cells and the positive and negative

regulatory receptors expressed on T cells.

• CD28 ligation co-stimulatory

effects

• CTLA-4 inhibitory effects (Tregs)

• The balance of CD28 and CTLA-4 derived

signals is critical to T cell activation and

tolerance.

• Regulatory T cells can effect the functional inactivation

of otherwise competent T cells

IMMUNOLOGICAL

TOLERANCE

Tolerance by Immune Suppression – Treg

cells

AUTOIMMUNE DISEASE

• When the mechanisms

controlling and maintaining

tolerance function poorly or

breakdown, autoimmunity

and autoimmune disease can develop

• Mechanism: Unclear

Probably multifactorial

Drugs

Viral illness

• Most associated with autoantibodyproduction

• Some due to cell mediated immune (CMI) responses

THE AETIOLOGY OF AUTOIMMUNITY

Induction of Autoimmunity -

1. Cooperation between autoreactive B-cells

and non- autoreactive T-cells

• Autoreactive B-cells - Efficient antigen presenting cells (APCs). May present antigen to non-autoreactive T-cells

• Part of the cross-reactive antigen has an epitope that normal (non-autoreactive) T cells recognise. This processed antigen is now capable of stimulating T-cells and provides “help” for autoreactive B cells

THE AETIOLOGY OF AUTOIMMUNITY

Induction of Autoimmunity

-

2. Molecular Mimicry

T-cells may be induced toprovide help aftercoming into contact witha microbial epitopewhich cross-reacts withself-antigens

3. Modification of autoantigen

The administration of drugs or defects in synthesis could result in the modification of a previously tolerised epitope, rendering it antigenic

Not commonly reported

• Autoimmune hemolytic anaemia following treatment with -methyldopa

• Isoniazid may produce arthritis, associated with production of anti-nuclear antibodies

• Procainamide induces anti-nuclear antibodies in a high proportion of patients, with 40% showing clinical signs of SLE

Th

T/B

Antigen

on APC

surface

Th

THE AETIOLOGY OF AUTOIMMUNITY

Autoimmunity

• Autoimmune disease usually arises spontaneously and persists, leading to long term damage.

• Can be Organ-Specific such as Hashimoto’s thyroiditis with organ-specific autoantibodies

• Or: the lesions are localised to a single organ but the autoantibodies are not organ-specific eg Primary Biliary Cirrhosis

• Or Non-Organ Specific diseases, where lesions and auto-antibodies are not confined to any one organ e. g. rheumatological disorders such as Systemic Lupus Erythematosus (SLE)

Organ-specific

Non organ-specific

Hashimoto’s thyroiditisprimary myxoedemathyrotoxicosispernicious anaemiaAddison’s diseaseT1DGoodpasture’s syndromemyasthenia gravispemphigoidmultiple sclerosis (?)autoimmune haemolytic anaemiaidiopathic thrombocytopenic purpuraidiopathic leucopeniaprimary biliary cirrhosisactive chronic hepatitis (HBsAgnegative)ulcerative colitisSjögren’s syndromerheumatoid arthritisdermatomyositissclerodermamixed connective tissue diseasesystemic lupus erythematosus

Either Antibody or T-Cells Can Cause Tissue Damage in Autoimmune

Disease

T-Cells Specific for Self Antigens Can Cause Direct Tissue Injury and Playa

Role in Sustained AutoantibodyResponses

AUTOIMMUNE DISEASE

Systemic - A response against auto-antigens not restricted to single organ

DISEASE AUTOANTIGEN

Systemic lupus

erythematosue (SLE)

Nuclear antigens

Cellular cytoplasmic antigens

PhospholipidsRed blood cell and platelet antigens

Rheumatoid Arthiritis Immunoglobulin

Sicca syndrome

(Sjögren’s syndrome)

Components of exocrine glands

Nuclear antigens – especially anti-Ro

(SSA) and anti-La (SSB)

SYSTEMIC LUPUS ERYTHEMATOSUS (SLE)

• Chronic multi-system inflammatory disorder

• Unknown aetiology

• Occurs predominantly in females (10:1)

• Spectrum of clinical course:

Mild Severe

May be fatal

• It is associated with:

- Uncontrolled interaction between T and B cells - Polyclonal B-cell activation

- Anti-nuclear antibodies (ANA)

- Probable defects in regulationof B-cells +/- T-cells

IMMUNOPATHOGENESIS OF SLE

Predisposition to develop SLE appears to be multi-factorial

There is a strong genetic basis

The development of SLE is a multi-step process

Hallmark -

The production of anti-nuclear antibodies - ANA’s

ANA’s are IgG autoantibodies directed against nuclear antigens

The presence of numerous auto-antibodies, particularly ANA’s

due to

and

- breakdown in immune surveillance

- loss of self tolerance

Hep-2 Cells

Add Patient’s Serum

Anti-nuclear IgG (ANA) in Patient’s Serum Binds to Nucleus

DETECTION OF ANA IN PATIENT’S SERUM

Fluorescein LabelledAnti-IgG Detects ANA

Add Fluorescein-Labelled

Anti-IgG

PATTERNS OF ANA BY IIF

Homogeneous Anti-DNA-histonecomplex (SLE,

drug- induced

lupus)

Anti-proteins of

nuclear envelope (Predominantly in

SLE)

Rim/Peripheral

Anti-antigens in thenucleus (the ENAs)(SLE, DL, MCTD, SS,

Scleroderma)

Speckled Anti-RNA Polymerase(predom. in

Scleroderma)

Nucleolar

ANA IN HEALTH AND NEWLY DIAGNOSEDSLE

A positive ANA test is NOT specific for SLE or any other connective tissue disease

Negative ANA or ANA at low dilution – 1:40 –Excludes SLE

< 2.5 2.5 105 15

HEALTH (196)

SLE (45)

Cu

mu

lati

ve f

req

ue

ncy

(%)

7.5

1:40

> 30

1:2560

20 30

1:12801:320

100

9080

70605040

3020100

ANA IU/ml

TITRE

ANA TITRE 1:40 1:320

Frequency in Heathy 32% 2%

Sensitivity for Diagnosis of SLE 97% 87%

Specificity for Diagnosis of SLE 68% 95%

KEY CONCEPTS OF SLE

Autoantibodies Mediate Pathology of SLE

By binding to cell surface antigens

Red blood cells - Haemolytic anaemia Platelets - Autoimmune thrombocytopenia Neutrophils and lymphocytes - Leukopenia Neuronal cells - Diffuse CNS disease

Direct Coomb’s Test

Used to detect the

presence of IgG or C3

bound to RBC’s

KEY CONCEPTS OF SLE

Autoantibodies Mediate Pathology of SLE By forming immune complexes that are then deposited in

tissues and interfere with function or cause tissue

damage by complement activation

DNA-anti-DNA Lupus nephritis Vasculitis? – arthritis

? – pneumonitis

By poorly understood mechanisms of disease association

Anti-phospholipid – Thrombosis(? inhibition of anticoagulant pathways)Anti-SS-A/Ro – Photosensitivity / rash / neonatal lupus

AUTOIMMUNE DISEASE

Organ Specific - A response against auto-antigens presentin single organ or system

DISEASE AUTOANTIGEN

Grave’s Disease TSH receptor of thyroid

Myasthenia GravisAcetyl choline receptor of skeletal

muscle

Diabetes Mellitus Components of pancreatic islet cells

PemphigusIntercellular substance of epidermis

and mucosal stratified epithelium

ORGAN-SPECIFIC AUTOIMMUNITY:THYROID AUTO-IMMUNE DISEASE

THYROID AUTO-IMMUNE DISEASE

Relatively common

1-2% of UK and USA populations

Subclinical disease in ~ 15%

Two categories:

a) Hyperthyroidism -

b) Hypothyroidism -

Grave’s disease

Hashimoto’s thyroiditis

Primary hypothyroidism

GRAVE’S DISEASE

Commonest cause ofhyperthyroidism

Peak incidence- 3rd and 4th decades

0.1 - 0.5% of population

Predisposing factors:

Living in areas of high iodine intake

Being female (F : M = 7 : 1)

PATHOGENESIS OF GRAVE’S DISEASE

1. Thyroid Stimulating Hormone (TSH) Receptor Antibodies (Thyroid Stimulating Immunoglobulins(TSI))

IgG

Compete with TSH for receptor binding

Stimulate glandular function ---> Hyperthyroidism

Titre correlates well with severity

Can cross placenta - Neonatal hyperthyroidism

2. Dense lymphocytic infiltrate -

Autoreactive CD4+ T-cells

?? Help B-cells to produce

autoantibodies

Normal Thyroid

PATHOGENESIS OF GRAVE’S DISEASE

HASHIMOTO’S THYROIDITIS

• Chronic inflammatory disease of

thyroid -autoimmune factors play

a prominent role

• Incidence - ~ 0.5% in general

population

• Peaks - Middle age

F >> M (20:1)

HASHIMOTO’S THYROIDITIS

• Evidence of participation of autoimmune factors:

• Lymphocytic infiltration of the gland

• Increased concentrations of immunoglobulins and antibodies against several components of thyroid tissue

• High titre of anti-Thyroid Peroxidase antibody

• Almost always present

• Also occur in other thyroid disorders, such as Graves' disease, but with lesser frequency

• In pregnant women, may be associated with higher risk for miscarriage, independent of the thyroid status

PATHOGENESIS OF HASHIMOTO’S THYROIDITIS

1. Dense lymphocytic infiltrate -

CD4+ and CD8+ T-cells

Macrophages, plasma cells

20 lymphoid follicles

and germinal centres

Possibility of strong T-cell mediated

cytotoxic reactions

CD4+ T-cells may help B-cells toproduce anti-thyroid autoantibodies

PATHOGENESIS OF HASHIMOTO’S THYROIDITIS

2. Autoantibodies

Antigens may be exposed on surface of thyroid follicular cells

3. Complement fixation - IgG autoantibodies

4. Antibody-dependent cytotoxicity

HASHIMOTO’S THYROIDITIS AUTOANTIBODIES

Two main autoantibodies

1. Anti-thyroid peroxidase (TPO)

2. Anti-thyroglobulin (TG)

Not 100% specific for Hashimoto’s thyroiditis

Valuable exclusionary test in patients with thyroid disease

• > 98% with thyroiditis have one or both of theseantibodies

• A negative result excludes diagnosis of thyroiditis

MECHANISM OF AUTOIMMUNITY IN HASHIMOTO’S THYROIDITIS

Current Genomics, 2011, 12, 576-

588

1. Anti-thyroid peroxidase(Anti-microsomal)

High titre in circulation and

apical border of thyroid cell

Two possible roles:

a) Kill thyroid cells in

presence of complement

b) Bind to and interfere with

function of peroxidase

HASHIMOTO’S THYROIDITISAUTOANTIBODIES

2. Anti-thyroglobulin Unlikely to have pathogenic roleUsually in low titre Do not appear to fix complement

Autoantibodies to Receptors Alter Receptor Function,

Causing Disease:

Stimulating (Hyperthyroidism) or Blocking (Hypothyroidism)