autoimmunity and autoimmune disorders

AUTOIMMUNITYAND AUTOIMMUNE DISORDERSDEPARTMENT OF BIOCHEMISTRY

DR JYOTI SHARMA

Introduction• Under normal circumstances immune system will not

destroy self antigens.

Autoimmunity can be defined as breakdown of mechanisms responsible for self tolerance and induction of specific adaptive immune response against components of the self.

Inability to eliminate antigen leads to chronic inflammatory process

• Ehrlich termed this horror autotoxicus

Immunity

Autoimmune Response

• Antibody directed against “self”, termed auto-antibody

• Considered abnormal but usually does not result in disease.

• May occur in healthy individuals.

Autoimmune Disease

• Disorder in which tissue injury is caused by an immunologic reaction of the host to its own tissues.

• Precise mechanisms unknown.• Classified as systemic or organ

specific, frequently have overlap.

About 2% of the population are affected by such diseases

Autoimmunity involves T cells

Ability of a T cell to respond is determined by MHC genotype It has been hypothesized that susceptibility to

an autoimmune disease is determined by differences in the ability of allelic variants of MHC molecules to present autoantigenic peptides

Alternatively, self peptides may drive the positive selection of developing thymocytes that are specific for particular autoantigens.

Levels of autoantigens may drive T cell selection

If antigens are expressed at too low a level, they may not drive negative intrathymic selection, but sufficient to drive positive selection

Insulin genes transcribed at high level in thymus protect against diabetes

Elimination of autoreactive B

cells in germinal centers

Layers of Self Tolerance• Self tolerance depends on the concerted and synergistic

action of a variety of mechanisms • Succession of checkpoints

PeripheralTolerance

Proposed Mechanisms

• Forbidden clone• Altered antigen• Sequestered Antigen• Immunologic deficiency theory• Genetic influence

There is a breakdown of self tolerance in these individuals by:

Forbidden clone

• Clone of changed or altered lymphocytes arise through mutation.

• Lack foreign surface antigens, not destroyed.

• Because of alteration may recognize host as foreign.

Altered Antigen

• Surface antigens on host altered by chemical, biological or physical means.

• This new antigenic determinant may be recognized as foreign by the host.

Sequestered Antigen

• Some antigens in the body are hidden from cells of the immune system.

• If there is damage to these organs causing exposure of these sequestered antigens an immune reaction to these antigens may occur.

Antigens in Immunologically Privileged Sites Can become

TargetNormally• Immunologically privileged sites are

not under constant immune surveillance

• Extracellular fluid does not pass through lymphatic system

• No naïve lymphocytes around those tissues

• Presence of inhibitory cytokines like TGFb

• Expression of fas ligand in these tissues

Post trauma and infection• Tissue barrier disrupted• Access of self reactive lymphocytes

to the sites• Infection/inflammation provide co-

stimulatory signal• Immune response against self

Sympathetic Ophthalmia

Immunologic Deficiency Theory

• Relates the increased frequency of auto-antibodies and increased immune system deficiency to age.

• Mutation or loss of immune regulatory powers results in the condition in which self antigens behave as foreign antigens.

Genetic Influence

• It is well recognized that certain immune disorders predominate in females and in families.

• Determined by family studies.• Genetic links have occurred

between diseases and HLA antigens

Population studies show association of susceptibility to insulin-dependent diabetes

mellitus (IDDM) with HLA genotype

Association of HLA Serotype and Sex with Susceptibility to Autoimmune Diseases

Hip jointsEyes

KidneysCNS

ThyroidMuscles

SystemicPancreas

Small joints

SkinThyroid

Gene Defects Associated with Autoimmune Diseases

• Predisposition to most autoimmune diseases due to combined effects of multiple genes including–Cytokines–CTLA-4, an inhibitory T Cell surface

molecule–Complement factors

Small number of autoimmune diseases with a single gene mutation

Fas Block in apoptosisFailure of apoptotic death of self reactive B and T lymphocytesAutoimmune lymphoproliferative syndrome

AIRE (autoimmune regulator gene)Transcription factorRegulates expression of tissue specific antigens by CD in thymus.If absent decreased expression of self antigens in thynmusDefective negative selection of self reactive thymocytesAutoimmune polyendocrinopathy- candidiasis-ectodermal dystrophy

Contributing Factors• Defects in the immune system.• Influence of hormones• Environmental conditions

• Defects in natural killer cells, in the secretion of ILs, in phagocytosis and complements may also contribute

• Hormones especially estrogen have been found to enhance B-cell activation and suppress regulator activities of T cell

• Environmental conditions such as infectious agents like viruses, bacteria and drugs contribute to autoimmunity

Hormones and Autoimmune Diseases

• The biggest difference in gender is observed between menarche and menopause

• Relatively more females affected during the years of cycling

• Intensified during pregnancy in affected women

Autoimmune Diabetes Mouse Model

Several ways in which infectious agents could break

self tolerance

Control of Autoimmune Responses by Regulatory T Cells

• Regulatory T cells can suppress self reactive lymphocytes that react to an antigen different from those recognized by themselves.

• Regulatory tolerance = dominant immune suppression.

• Defects in regulatory T cell activity are associated with certain autoimmune diseases– Multiple sclerosis

Secondary Effects of Autoimmune Reactions

• Deposit of immune complexes

• Complement activation triggering inflammation

• Removal of complement -covered antigen by erythrocytes

• Sequestration in spleen, liver

30

Classification of Autoimmune Diseases by Localization

Mysthenia gravis, aiha,good pasturesGraves diseasesjogren

Myasthenia Gravis• 80 to 90% of patients have Autoantibodies against

acetylcholine receptor• Combination of the Abs to the receptors blocks the

binding of acetylcholine which destroy the receptors• Muscle weakness• Repetitive movements very difficult!• In particular eye bulb muscles affected• Life threatening when muscles for respiration are

affected• Can be transferred to fetus .• Abs can be detected with RIA methods Anticholinesterase agents are employed in therapy

Organ sp and type 2

Grave’s Disease• Autoantibodies against receptor for

thyroid stimulating hormone (TSH)• Activate receptor leading to excessive

thyroid hormone production• Women are more susceptible than men

by a margin of 7:1 and usually present between the ages of 30 and 40.

• In whites, the disease is associated with the HLA antigen DR3 while in Asians HLA Bw35 and Bw36 occur more frequently

Organ sp and type 2

• HLA DQB1 appears to confer resistance to the disease

• Clinical Signs:• Disease is presented as thyrotoxicosis with a

diffusely enlarged goiter that is soft instead of rubbery

• Signs include nervousness, insomnia, depression, weight loss, heat intolerance, sweating, rapid heart beat

• Other signs include fatigue, cardiac dysrhythmias, restlessness, and exopthalmus

• Immunologic Findings:• The thyroid presents with Hyperplasia with a patchy

infiltration of lymphocytes• Both CD4 and CD8 cells are present and the T cells

appear to play a central role in the pathogenesis of the disease

• The most significant Ab present is thyroid stimulating hormone receptor antibody (TRab)

• Ag-Ab combination result in the stimulation of the receptor resulting in the release of the thyroid hormones

• Another group of Abs called thyroid stimulating antibodies or immunoglobulins (TSab or TSI) may

• have different specificity

• Laboratory Diagnosis:• A key finding in Graves’ disease is elevated

levels of total and free T3 and T4 • In addition, TSH levels are low due to Ab

stimulation of the thyroid• Measurement of the thyroid Abs may be

undertaken if the above assays are unclear• Treatment:• Antithyroid medication may be employed.

Radioiodine which emits beta particles may be used. Surgery is also an option.

Autoimmune Transfer

• From mother to fetus through placenta• Often during pregnancy increased disease

activity• Child is born with symptoms of mother’s

disease• Graves’ disease, myasthenia gravis

T-Cell Mediated Autoimmune Disease: Diabetes Mellitus Type I

• Insulin Dependent Diabetes Mellitus (IDDM)• Early, sudden onset (adolescence)• Initially mediated by autoantibodies against b-cell

antigen• Later phases include cytotoxic T-cell response• About 95% of white diabetics carry the HLA-DR3 or

DR4 genes• It appears that true susceptibility genes for IDDM

may occur in the HLA-DQ region

Organ sp and type 4

Immunohistochemistry Insulin = brown

Glucagon = black

Insulin-Dependent Diabetes

• Viral infections have been linked with diabetes• Mumps virus, rubella virus, CMV, and Coxsakie B4

virus have all been inconclusively linked to diabetes • Congenital rubella infection is the only one for which

a link has been definitively identified• There appears to be similarity between coxsakie

viral protein P2-C and the enzyme glutamic acid decarboxylase.

• Antibodies are formed against glutamic acid decarboxylase in IDDM

• Molecular mimicry could initiate Ab production against self Ag

• Immunopathology:• Inflammation of the islets of Langerhans in the

pancreas leads to fibrosis and destruction of most of the beta cells

• CD4 and CD8 B cells and macrophages are all involved in the destructive process of the islet cells• Laboratory Testing:

• IDDM is usually diagnosed by the presence of hyperglycemia

• Abs to islet cells may be screened for by indirect IFA with human or rat islet cells

• Islet cell may be detected in the sera of newly diagnosed diabetic cases

• Abs to insulin may be detected by ELISA or • RIA methods

• Treatment:• Insulin has been the standard form of

treatment• New treatment methods center around the

use of immunosuppressive agents• Agents that have been tried include

azathioprine, cyclosporine A and prednisone • All these agents have potentially toxic effects

Systemic Lupus Erythematosus• It is a chronic systemic inflammatory disease

marked by alternating exacerbation and remissions

• Approximately 1 in every 2000 individuals are affected

• Age of onset is usually b/w 20 and 40 yrs of age

• Women are much more likely than men to be stricken by a margin of 13 to 1

• Etiology is unknown but may be due to genetic and environmental factors

• In whites, it is strongly associated to with HLA-DR3 or DR2 and DQB1

nonOrgan sp and type3

• Auto-antibodies against nuclear components (DNA, histones, ribosomes, snRNP, etc)

• Immune complexes activate complement

• Complexes transported via Fc-rec. on phagocytes or via complement rec. on erythrocytes to spleen/liver for sequestration

• Excess complexes are deposited in small blood vessels

• Local inflammation in skin, joints and kidneys, multi-organ damage

• May lead to activation of self reactive T lymphocytes

• Clinical Signs:• The first signs to appear are usually

nonspecific such as fatigue, weight loss, malaise, fever, and anorexia

• Joint involvement of small joints of the hands, wrist and knees is reported in over 90% of cases

• A skin manifestation of an erythematous rash may appear in the area of body exposed to UV light

• A classic butterfly rash across the nose and cheeks which is responsible for the name lupus may appear

• Some patients may also exhibit renal involvement

• Renal involvement is usually in the form of lesions the most dangerous of which is glomerulonephritis

• Immune complexes may deposit in the subendothelial tissue and thickening of the basement membrane results

• All of these can result in renal failure and death

• There might also be cardiac involvement with pericarditis, tachycardia, or ventricular enlargement.

• CNS manifestation such as seizures, psychoses, or depression

• Hematologic abnormalities such as anemia,

• leukopenia or lymphopenia are exhibited .

• Immunological Findings:• The LE cell was discovered by Malcolm and

Hargraves in 1948.• The LE cell is a neutrophil that has engulfed the

antibody-coated nucleus of another neutrophil• SLE is associated with more than 28

autoantibodies• Lupus patients appear to have overactive B cells

especially the subset with the CD5 marker which increase in number

• Complement is activated which results in decrease in the serum level of complement components

• At the same time there is an increase in the level of breakdown products of complements such as C3d and C3a

• IgG is most pathogenic and it forms complexes that are deposited in the glomerular basement membrane

• Accumulation of immune complex with complement activation is responsible for the damage to the kidney

• Drug induced lupus differs from the chronic form of the disease: when the drug is withdrawn symptoms disappear

• It is a milder form of the disease and manifest as arthritis or rashes

• Drugs that have been implicated include procainamide hydrochloride, hydralazine hydrochloride, methyldopa etc.

• Laboratory Diagnosis of SLE:• A screening test for antinuclear antibody

(ANA) is usually the first test done• 1.Fluorescent antinuclear antibody

(FANA) testing is most widely used• The test is sensitive but the specificity is low

because many of the Abs are associated with other diseases

• About 5% of healthy individuals and b/w 10 and 30% of elderly individuals test positive

• If FANA is positive, then a profile testing should be done for individual Abs

• More than 99% of patients with SLE will have• a positive result for one or more tests

• 2.Double-stranded DNA (ds-DNA):• These Abs are the most specific for SLE and

are seen only in patients with SLE• Found in only 50 to 80% of cases but when

seen, they are diagnostic of the disease• Abs to ds-DNA produce a peripheral staining

pattern in IFA• A sensitive assay for ds-DNA utilizes Crithidia

luciliae, a hemoflagellate as the substrate• A positive test is indicated by a brightly

stained kinetoplast with a dilution of 1:10 or greater of patient serum

• 3.Antihistone antibody:• Histone is a major component of chromatin• This antibody is found in lupus patients • It binds to DNA and may be found in all cases of

drug induced lupus• If no other Abs are present, this may support a

diagnosis of drug induced lupus• The Abs may be detected by IFA, RIA or EIA

• 4.Antibodies are also produced against DNA complexed to histone known as deoxyribonucleoprotein (DNP)

• The antibody is thought to be identical to the LE factor or phenomenon

• It appears in 70 to 90% of patients with SLE

• A slide method using latex particle coated with DNP have been used in a simple slide agglutination test for SLE

4.Anti-Sm antibody:• Antibody to extractable nuclear antigen was first

described in a patient named Smith hence it is called anti-Sm

• Extractable nuclear Ags are small nuclear riboproteins that are associated with uridine-rich ribonucleic acid (RNA)

• The Ab is specific for SLE and not found in other autoimmune diseases

• Anti-Sm can be measured by double diffusion, passive hemagglutination, and EIA

• SS-A/Ro and SS-B/La are also members of the family of extractable nuclear antigens.

• Antibody to SS-A/Ro appears in 25 to 40% of patients with SLE

• It is found in patients with cutaneous manifestations of SLE

• SS-B/La is found in 10 to 15% of patients with SLE and all of them have anti-SS-A/Ro

• Antibodies are detected by the IFA test with the use of human tissue culture cells e.g. (Hep-2) human epidermal

• 6.Anti-nRNP:• Anti-nRNP produces a finely speckled IFA pattern • RNP is a nuclear RNA which is found in association with

seven to eight nonhistone proteins

• The antibody is also found in high titer in individuals with mixed connective tissue disease and other autoimmune diseases

• The antibody can be measured by double diffusion, passive hemaglutination and EIA and IFA

Treatment:• If the primary symptom is fever or arthritis a high

dose of aspirin or other anti-inflammatory drug may bring relief

• May also use antimalarials and topical steroids. Other drugs include cyclophosphamide, methotrexate etc.

Rheumatoid Arthritis• Rheumatoid arthritis is a systemic autoimmune

disorder• It involves the synovial membrane of multiple joints• Women are more likely to be affected than men and

usually strikes between the ages of 20 and 40• Spontaneous remission may be experienced by

some patients otherwise the disease may progress and result in deformity and disability

• RA has been associated with certain of the HLA class II molecules.

• HLA-DR1 and DR4 occur in 70% of patients with with RA

nonOrgan sp and type3

Clinical Signs:• Diagnosis of RA is based on the

1987 criteria established by the American

College of Rheumatology • Symptoms include morning

stiffness around the joints lasting at least 1 hour, swelling of the soft tissue around three or more joints

Others include swelling of the proximal interphalangeal, metacarpophalangeal, or wrist joints, symetric arthritis, subcutaneous nodules, a positive RF test Also included is a radiographic evidence of erosion of the joints of the hands, the wrist, or

both

• Usually begins with nonspecific symptoms such as fever, malaise, weight loss, and transient joint pain

• Stiffness and joint pain that gradually improves during the day are characteristics exhibited by most patients

• Joint are involved progressively to larger joints in a symmetric manner from the knees, hips, elbows, shoulders and cervical spine

• About 25% of patients have nodules over the bones

• Nodules may also be found in the myocardium, pericardium, heart valve, pleural, lungs, spleen, and larynx

• Immunologic Findings:

• The main immunologic finding is the presence of RF• RF is a 19S Ab directed against the Fc portion of IgG• The Ab is not specific for RA as it is found in other

diseases such as SLE, scleroderma, Sjögren’s syndrome and B cell lymphoproliferative disorders

• It has been suggested that RF may be anti-idiotypic antibodies involved in the regulation of immune response

• In RA, polyclonal activation of B cells may occur resulting in overwhelming amount of antibody to IgG

Rheumatoid FactorIgG Molecule

Fc Portion

Antigen Binding Groove

IgM Molecule

Autoantibodies (IgM) directed against the Fc Fragment of IgG

An Antibody to an Antibody

Their Role in RA is not understood

• Other autoAbs associated with RA include ANA, anticollagen Abs, Abs against cytoskeleton filamentous proteins etc.

• These Abs may cause immune complex formation with the activation of complement which contribute to pathogenesis

• Joint damage is due to invasion of inflammatory cells such as neutrophils, and macrophages

• Proliferation of fibroblast, macrophages, mast cells, and stellar cells result in the formation of a pannus, an organized mass of cells that grow into the joint space

• Laboratory Diagnosis of Rheumatoid Arthritis:

• Diagnosis is based on a combination of clinical manifestations, radiographic findings and lab tests

• Laboratory screening test for RF using sheep red cells or latex particles are available and simple to perform

• Quantitative test are also available which involve nephelometry and ELISA techniques

• RF is found in other diseases such as syphilis, viral infections, leprosy, chronic liver disease, neoplasm and other inflammatory processes

• The RF test is thus not a specific test for RA and about 10% of patient with the disease test negative for RF

• C-reactive protein and ESR are usually elevated and complements are normal or elevated

• Treatment:• Treatment include palliatives with rest and

nonsteroidal anti-inflammatory drugs like salicylates and ibuprofen

• Slow-acting antirheumatic drugs (SAARDS) may also be used to treat the condition

• New therapy include the use of monoclonal Abs that target T cells

SYSTEMIC SCLEROSIS Systemic sclerosis (SSc) is a

chronic multisystem disorder of unknown etiology characterized clinically by thickening of the skin caused by accumulation of connective tissue and by structural and functional abnormalities of visceral organs, including the gastrointestinal tract, lungs, heart, and kidneys.

Epidemiology The estimated incidence of

systemic sclerosis is 19 cases per million population, and the prevalence of systemic sclerosis has been estimated at 240 cases per million population, although reported prevalence has ranged from 138 to 286 cases per million population. The risk of systemic sclerosis is 3-9 times higher in women than in men. The peak onset occurs in individuals aged 30-50 years.

Etiology • 1. Genetic abnormalities. • 2. Infectious agents.• 3. Environmental factors.• 4. Drugs.

Pathogenesis

Pathology • Systemic sclerosis is

characterized by excessive fibrosis in the skin and other affected organs. The skin and lungs also show prominent T-lymphocyte infiltration. A severe fibroproliferative vasculopathy that affects small arteries and arterioles is universally present in affected organs. Platelet microthrombi are often found in the lumen of the narrowed vessels.

Classification1. Systemic sclerosis:• Limited cutaneous disease• Diffuse cutaneous disease• Sine scleroderma• Undifferentiated connective tissue

disease• Overlap syndromes2. Localized scleroderma• Morphea• Linear scleroderma (en coup de sabre)

Clinical Manifestations Skin Features

• Tightening of the skin in the face, with a characteristic beaklike facies and paucity of wrinkles

Clinical Manifestations Skin Features

• Sclerodactyly with digital ulceration, loss of skin creases, joint contractures, and sparse hair

Clinical Manifestations Skin Features

• Anterior chest demonstrating salt-and-pepper hypopigmentation and diffuse hyperpigmentation in a white woman

Clinical Manifestations • Raynaud’s Phenomenon • Musculoskeletal Features • Gastrointestinal Features • Pulmonary Features • Cardiac Features • Renal Features

Workup

Workup• CT scan • Radiography • Echocardiography • Right-heart catheterization • Esophagraphy • Pulmonary function testing • Serum N-terminal pro-brain natriuretic

peptide • Cardiac rhythm monitoring • Esophagogastroduodenoscopy • Biopsy of skin and lungs