Introduction• Under normal circumstances immune system will notdestroy self antigens.Autoimmunity can be defined as breakdownof mechanisms responsible for selftolerance and induction of specificadaptive immune response againstcomponents of the self.Inability to eliminate antigen leads to chronicinflammatory process• Ehrlich termed this horror autotoxicus
Autoimmune Response• Antibody directed against “self”, termedauto-antibody• Considered abnormal but usually does notresult in disease.• May occur in healthy individuals.
Autoimmune Disease• Disorder in which tissue injury is causedby an immunologic reaction of the hostto its own tissues.• Precise mechanisms unknown.• Classified as systemic or organspecific, frequently have overlap.About 2% of the population areaffected by such diseases
Autoimmunity involves T cells Ability of a T cell to respond is determined byMHC genotype It has been hypothesized that susceptibility to anautoimmune disease is determined by differencesin the ability of allelic variants of MHC moleculesto present autoantigenic peptides Alternatively, self peptides may drive the positiveselection of developing thymocytes that arespecific for particular autoantigens.
Levels of autoantigens maydrive T cell selectionIf antigens are expressed at too low alevel, they may not drive negativeintrathymic selection, but sufficient todrive positive selectionInsulin genes transcribed at high level inthymus protect against diabetes
Layers of Self Tolerance• Self tolerance depends on the concerted and synergistic actionof a variety of mechanisms• Succession of checkpointsPeripheralTolerance
Proposed Mechanisms• Forbidden clone• Altered antigen• Sequestered Antigen• Immunologic deficiency theory• Genetic influenceThere is a breakdown of self tolerance inthese individuals by:
Forbidden clone• Clone of changed or alteredlymphocytes arise through mutation.• Lack foreign surface antigens, notdestroyed.• Because of alteration may recognizehost as foreign.
Altered Antigen• Surface antigens on host altered bychemical, biological or physical means.• This new antigenic determinant may berecognized as foreign by the host.
Sequestered Antigen• Some antigens in the body are hiddenfrom cells of the immune system.• If there is damage to these organscausing exposure of thesesequestered antigens an immunereaction to these antigens may occur.
Antigens in ImmunologicallyPrivileged Sites Can become TargetNormally• Immunologically privileged sites are notunder constant immune surveillance• Extracellular fluid does not passthrough lymphatic system• No naïve lymphocytes around thosetissues• Presence of inhibitory cytokines likeTGF• Expression of fas ligand in thesetissuesPost trauma and infection• Tissue barrier disrupted• Access of self reactive lymphocytes tothe sites• Infection/inflammation provide co-stimulatory signal• Immune response against self
Immunologic DeficiencyTheory• Relates the increased frequency ofauto-antibodies and increasedimmune system deficiency to age.• Mutation or loss of immuneregulatory powers results in thecondition in which self antigensbehave as foreign antigens.
Genetic Influence• It is well recognized that certainimmune disorders predominate infemales and in families.• Determined by family studies.• Genetic links have occurred betweendiseases and HLA antigens
Population studies show association ofsusceptibility to insulin-dependent diabetesmellitus (IDDM) with HLA genotype
Association of HLA Serotype and Sex withSusceptibility to Autoimmune DiseasesHip jointsEyesKidneysCNSThyroidMusclesSystemicPancreasSmall jointsSkinThyroid
Gene Defects Associated withAutoimmune Diseases• Predisposition to most autoimmunediseases due to combined effects ofmultiple genes including– Cytokines– CTLA-4, an inhibitory T Cell surfacemolecule– Complement factors
Small number of autoimmune diseases witha single gene mutationFasBlock in apoptosisFailure of apoptotic death of self reactive Band T lymphocytesAutoimmune lymphoproliferative syndromeAIRE (autoimmune regulator gene)Transcription factorRegulates expression of tissue specific antigensby CD in thymus.If absent decreased expression of self antigensin thynmusDefective negative selection of self reactivethymocytesAutoimmune polyendocrinopathy- candidiasis-ectodermal dystrophy
Contributing Factors• Defects in the immune system.• Influence of hormones• Environmental conditions
• Defects in natural killer cells, in the secretion ofILs, in phagocytosis and complements may alsocontribute• Hormones especially estrogen have been found toenhance B-cell activation and suppress regulatoractivities of T cell• Environmental conditions such as infectiousagents like viruses, bacteria and drugs contributeto autoimmunity
Hormones and AutoimmuneDiseases• The biggestdifference in genderis observed betweenmenarche andmenopause• Relatively morefemales affectedduring the years ofcycling• Intensified duringpregnancy in affectedwomenAutoimmune Diabetes Mouse Model
Several ways in which infectiousagents could break self tolerance
Control of Autoimmune Responsesby Regulatory T Cells• Regulatory T cells can suppress self reactivelymphocytes that react to an antigen differentfrom those recognized by themselves.• Regulatory tolerance = dominant immunesuppression.• Defects in regulatory T cell activity areassociated with certain autoimmune diseases– Multiple sclerosis
Secondary Effects ofAutoimmune Reactions• Deposit of immunecomplexes• Complement activationtriggering inflammation• Removal of complement-covered antigen byerythrocytes• Sequestration in spleen,liver
Myasthenia Gravis• 80 to 90% of patients have Autoantibodies againstacetylcholine receptor• Combination of the Abs to the receptors blocks the bindingof 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 methodsAnticholinesterase agents are employedin therapyOrgan sp and type 2
Grave’s Disease• Autoantibodies against receptor for thyroidstimulating hormone (TSH)• Activate receptor leading to excessivethyroid hormone production• Women are more susceptible than men by amargin of 7:1 and usually present betweenthe ages of 30 and 40.• In whites, the disease is associated with theHLA antigen DR3 while in Asians HLA Bw35and Bw36 occur more frequentlyOrgan sp and type 2
• HLA DQB1 appears to confer resistance to thedisease• Clinical Signs:• Disease is presented as thyrotoxicosis with adiffusely enlarged goiter that is soft instead ofrubbery• Signs includenervousness, insomnia, depression, weightloss, heat intolerance, sweating, rapid heart beat• Other signs include fatigue, cardiacdysrhythmias, restlessness, and exopthalmus
• Immunologic Findings:• The thyroid presents with Hyperplasia with a patchyinfiltration of lymphocytes• Both CD4 and CD8 cells are present and the T cellsappear to play a central role in the pathogenesis of thedisease• The most significant Ab present is thyroid stimulatinghormone receptor antibody (TRab)• Ag-Ab combination result in the stimulation of thereceptor resulting in the release of the thyroidhormones• Another group of Abs called thyroid stimulatingantibodies or immunoglobulins (TSab or TSI) may• have different specificity
• Laboratory Diagnosis:• A key finding in Graves’ disease is elevated levelsof total and free T3 and T4• In addition, TSH levels are low due to Abstimulation of the thyroid• Measurement of the thyroid Abs may beundertaken if the above assays are unclear• Treatment:• Antithyroid medication may be employed.Radioiodine which emits beta particles may beused. Surgery is also an option.
Autoimmune Transfer• From mother to fetus through placenta• Often during pregnancy increased diseaseactivity• Child is born with symptoms of mother’s disease• Graves’ disease, myasthenia gravis
T-Cell Mediated AutoimmuneDisease: Diabetes Mellitus Type I• Insulin Dependent Diabetes Mellitus (IDDM)• Early, sudden onset (adolescence)• Initially mediated by autoantibodies against -cellantigen• Later phases include cytotoxic T-cell response• About 95% of white diabetics carry the HLA-DR3 orDR4 genes• It appears that true susceptibility genes for IDDMmay occur in the HLA-DQ regionOrgan sp and type 4
ImmunohistochemistryInsulin = brownGlucagon = black
Insulin-Dependent Diabetes• Viral infections have been linked with diabetes• Mumps virus, rubella virus, CMV, and Coxsakie B4 virushave all been inconclusively linked to diabetes• Congenital rubella infection is the only one for which alink has been definitively identified• There appears to be similarity between coxsakie viralprotein P2-C and the enzyme glutamic aciddecarboxylase.• Antibodies are formed against glutamic aciddecarboxylase in IDDM• Molecular mimicry could initiate Abproduction against self Ag
• Immunopathology:• Inflammation of the islets of Langerhans in thepancreas leads to fibrosis and destruction of mostof the beta cells• CD4 and CD8 B cells and macrophages are allinvolved in the destructive process of the islet cells• Laboratory Testing:• IDDM is usually diagnosed by the presence ofhyperglycemia• Abs to islet cells may be screened for by indirect IFAwith human or rat islet cells• Islet cell may be detected in the sera of newly diagnoseddiabetic 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 ofimmunosuppressive agents• Agents that have been tried includeazathioprine, cyclosporine A and prednisone• All these agents have potentially toxic effects
Systemic Lupus Erythematosus• It is a chronic systemic inflammatory diseasemarked by alternating exacerbation andremissions• Approximately 1 in every 2000 individuals areaffected• Age of onset is usually b/w 20 and 40 yrs of age• Women are much more likely than men to bestricken by a margin of 13 to 1• Etiology is unknown but may be due to genetic andenvironmental factors• In whites, it is strongly associated to with HLA-DR3 or DR2 and DQB1nonOrgan sp and type3
• Auto-antibodies against nuclearcomponents (DNA, histones,ribosomes, snRNP, etc)• Immune complexes activatecomplement• Complexes transported via Fc-rec.on phagocytes or via complementrec. on erythrocytes tospleen/liver for sequestration• Excess complexes are deposited insmall blood vessels• Local inflammation in skin, jointsand kidneys, multi-organ damage• May lead to activation of selfreactive T lymphocytes
• Clinical Signs:• The first signs to appear are usually nonspecificsuch as fatigue, weight loss, malaise, fever, andanorexia• Joint involvement of small joints of thehands, wrist and knees is reported in over 90% ofcases• A skin manifestation of an erythematous rashmay appear in the area of body exposed to UVlight• A classic butterfly rash across the nose andcheeks which is responsible for the name lupusmay appear• Some patients may also exhibit renal involvement
• Renal involvement is usually in the form of lesionsthe most dangerous of which is glomerulonephritis• Immune complexes may deposit in thesubendothelial tissue and thickening of thebasement membrane results• All of these can result in renal failure and death• There might also be cardiac involvement withpericarditis, tachycardia, or ventricularenlargement.• 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 andHargraves in 1948.• The LE cell is a neutrophil that has engulfed theantibody-coated nucleus of another neutrophil• SLE is associated with more than 28 autoantibodies• Lupus patients appear to have overactive B cellsespecially the subset with the CD5 marker whichincrease in number
• Complement is activated which results in decreasein the serum level of complement components• At the same time there is an increase in the levelof breakdown products of complements such asC3d and C3a• IgG is most pathogenic and it forms complexesthat are deposited in the glomerular basementmembrane• Accumulation of immune complex withcomplement activation is responsible for thedamage to the kidney
• Drug induced lupus differs from the chronicform of the disease: when the drug is withdrawnsymptoms disappear• It is a milder form of the disease and manifest asarthritis or rashes• Drugs that have been implicated includeprocainamide hydrochloride, hydralazinehydrochloride, 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 lowbecause many of the Abs are associated withother diseases• About 5% of healthy individuals and b/w 10 and30% of elderly individuals test positive• If FANA is positive, then a profile testing shouldbe 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 areseen 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 stainingpattern in IFA• A sensitive assay for ds-DNA utilizes Crithidialuciliae, a hemoflagellate as the substrate• A positive test is indicated by a brightly stainedkinetoplast with a dilution of 1:10 or greater ofpatient 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 druginduced lupus• If no other Abs are present, this may support adiagnosis of drug induced lupus• The Abs may be detected by IFA, RIA or EIA• 4.Antibodies are also produced against DNA complexedto histone known as deoxyribonucleoprotein (DNP)• The antibody is thought to be identical to the LEfactor or phenomenon• It appears in 70 to 90% of patients with SLE
• A slide method using latex particle coated with DNP havebeen used in a simple slide agglutination test for SLE4.Anti-Sm antibody:• Antibody to extractable nuclear antigen was firstdescribed in a patient named Smith hence it is calledanti-Sm• Extractable nuclear Ags are small nuclear riboproteinsthat are associated with uridine-rich ribonucleic acid(RNA)• The Ab is specific for SLE and not found in otherautoimmune diseases• Anti-Sm can be measured by double diffusion, passivehemagglutination, and EIA
• SS-A/Ro and SS-B/La are also members of the family ofextractable nuclear antigens.• Antibody to SS-A/Ro appears in 25 to 40% of patients withSLE• It is found in patients with cutaneous manifestations of SLE• SS-B/La is found in 10 to 15% of patients with SLE and allof them have anti-SS-A/Ro• Antibodies are detected by the IFA test with the use ofhuman 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 withseven to eight nonhistone proteins
• The antibody is also found in high titer in individuals withmixed connective tissue disease and other autoimmunediseases• The antibody can be measured by double diffusion,passive hemaglutination and EIA and IFATreatment:• If the primary symptom is fever or arthritis a high doseof aspirin or other anti-inflammatory drug may bringrelief• May also use antimalarials and topical steroids. Otherdrugs 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 andusually strikes between the ages of 20 and 40• Spontaneous remission may be experienced by somepatients otherwise the disease may progress and resultin deformity and disability• RA has been associated with certain of the HLA class IImolecules.• HLA-DR1 and DR4 occur in 70% of patientswith with RAnonOrgan sp and type3
Clinical Signs:• Diagnosis of RA is based on the 1987criteriaestablished by the American Collegeof Rheumatology• Symptoms include morning stiffnessaround the joints lasting at least 1hour, swelling of the soft tissuearound three or more jointsOthers include swelling of the proximalinterphalangeal, metacarpophalangeal, or wristjoints, symetric arthritis, subcutaneous nodules, a positive RFtestAlso included is a radiographic evidence oferosion of the joints of the hands, the wrist, orboth
• Usually begins with nonspecific symptoms such asfever, malaise, weight loss, and transient joint pain• Stiffness and joint pain that gradually improves duringthe day are characteristics exhibited by most patients• Joint are involved progressively to larger joints in asymmetric 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, andlarynx
• 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 otherdiseases such as SLE, scleroderma, Sjögren’s syndromeand B cell lymphoproliferative disorders• It has been suggested that RF may be anti-idiotypicantibodies involved in the regulation of immune response• In RA, polyclonal activation of B cells may occurresulting in overwhelming amount of antibody to IgG
Rheumatoid FactorIgG MoleculeFc PortionAntigen BindingGrooveIgM MoleculeAutoantibodies(IgM) directedagainst the FcFragment of IgGAn Antibody to anAntibodyTheir Role in RAis not understood
• Other autoAbs associated with RA include ANA,anticollagen Abs, Abs against cytoskeleton filamentousproteins etc.• These Abs may cause immune complex formation withthe activation of complement which contribute topathogenesis• Joint damage is due to invasion of inflammatory cellssuch as neutrophils, and macrophages• Proliferation of fibroblast, macrophages, mast cells, andstellar cells result in the formation of a pannus, anorganized mass of cells that grow into the joint space
• Laboratory Diagnosis of RheumatoidArthritis:• Diagnosis is based on a combination of clinicalmanifestations, radiographic findings and lab tests• Laboratory screening test for RF using sheep red cellsor latex particles are available and simple to perform• Quantitative test are also available which involvenephelometry and ELISA techniques• RF is found in other diseases such as syphilis, viralinfections, leprosy, chronic liver disease, neoplasm andother inflammatory processes
• The RF test is thus not a specific test for RA and about10% of patient with the disease test negative for RF• C-reactive protein and ESR are usually elevated andcomplements are normal or elevated• Treatment:• Treatment include palliatives with rest and nonsteroidalanti-inflammatory drugs like salicylates and ibuprofen• Slow-acting antirheumatic drugs (SAARDS) may also beused to treat the condition• New therapy include the use of monoclonal Abs thattarget T cells
SYSTEMIC SCLEROSISSystemic sclerosis (SSc) is achronic multisystem disorder ofunknown etiology characterizedclinically by thickening of the skincaused by accumulation of connectivetissue and by structural andfunctional abnormalities of visceralorgans, including the gastrointestinaltract, lungs, heart, and kidneys.
EpidemiologyThe estimated incidence ofsystemic sclerosis is 19 cases permillion population, and the prevalenceof systemic sclerosis has beenestimated at 240 cases per millionpopulation, although reportedprevalence has ranged from 138 to286 cases per million population. Therisk of systemic sclerosis is 3-9times higher in women than in men.The peak onset occurs in individuals
Pathology• Systemic sclerosis ischaracterized byexcessive fibrosis in theskin and other affectedorgans. The skin andlungs also showprominent T-lymphocyteinfiltration. A severefibroproliferativevasculopathy thataffects small arteriesand arterioles isuniversally present inaffected organs.Platelet microthrombiare often found in thelumen of the narrowedvessels.
Classification1. Systemic sclerosis:• Limited cutaneous disease• Diffuse cutaneous disease• Sine scleroderma• Undifferentiated connective tissuedisease• Overlap syndromes2. Localized scleroderma• Morphea• Linear scleroderma (en coup de sabre)
Clinical ManifestationsSkin Features• Tightening of theskin in the face, witha characteristicbeaklike facies andpaucity of wrinkles