Pathology: Autoimmunity
SLE (kidney, class III)
- normal glom (thin arrow) - necrosis (thick arrows) - global damage to glom (double arrow) - if you see normal glomeruli, then you're seeing this class
Sjögren syndrome (histo pic)
- over time, atrophy of salivary glands, replaced with fat - fibrosis + some infiltrate
Sjogren syndrome (enlarged salivary gland)
- parotid/submandibular glands swelling
Central tolerance breakdown
- *All autoimmune diseases* involve a *break in T cell tolerance* - healthy individuals also have autoreactive T cells that slip through but peripheral mechs prevent harm! - *Autoreactive T cells gain access to immune privileged sites* or tissues that T cells have not been selected against - Autoreactive B cells more common, not exposed to same rigorous self antigen array that T cells see - also, B cells change drastically in periphery - class switch, affinity maturation, somatic hypermutation
Systemic Sclerosis (Scleroderma)
- *Chronic inflammation (type IV)* thought to be result of autoimmunity - Widespread damage to *small blood vessels* - Progressive *interstital and perivascular fibrosis in skin, GI tract, kidneys, heart, muscles, lung* - More common in women 30 - 50 - *Organ malfunction* leads to death
SLE Immunofluorescence
- *Highly sensitive - Not highly specific* - Patterns are not absolutely specific for type of Ab - Antibodies to *DS DNA and to Smith (Sm) antigen* (non-DNA) are virtually diagnostic
Molecular mimicry - chronic
- *Self antigens mimic pathogen-derived peptide from previous infection*, stim T cells --> chronic condition - TCR:antigen:MHC complex structure limits antigen size - *enhanced potential for cross reactivity* to self peptides when presentation occurs on same MHC allotype - T cell has more difficulty deciphering self and non-self antigens sharing sequence homology - Activated T cells = *migratory*, encounter additional cross reactive autoantigen in tissues following their activation w/ pathogen-derived antigen in lymph nodes
SLE: Genetic factors
- 25% concordance in monozygotic twins vs. 1 to 3% in dizygotic twins - Increased risk of developing disease in family members w/ 20% unaffected showing autoantibodies - Association of *HLA-DQ* locus + SLE - 6% have *inherited deficiencies of complement*
SLE Diagnostic Criteria
- ANA is key lab result!
Kidney in SLE
- Acute renal failure is most common cause of death - Glomerulonephritis 1) Class I *normal by LM*, immune complexes in mesangium by IF and EM (rare) 2) Class II mesangial lupus nephritis (20%): *capillaries normal* 3) Class III *focal proliferative* glomerulonephritis (25%) 4) Class IV *diffuse proliferative* glomerulonephritis (50%) *most serious, most common* 5) Class V *membranous* glomerulonephritis (15%) - only endothelium involved, linear pattern 6) Class VI *advanced sclerosing* lupus nephritis: end-stage renal disease
Autoimmune disease mechanisms
- All are type II, III, or IV hypersensitivities - pathology and severity are dependent on antigen and localization of response - autoimmune disease *almost always contain a T cell component, but not all are type IV hypersensitivities* - Conversely, *almost all type IV hypersensitivities contain B cell / autoAb component* - diseases are classified based on *what component is doing damage*
Systemic Sclerosis tests
- Anti Nuclear Protein Antibodies 1) *Scl-70* - highly specific Ab - Diffuse (systemic) scleroderma - *DNA topoisomerase 1* 2) *Anti-Centromere* Ab - Limited scleroderma (CREST)
General treatments for Autoimmunity
- Anti-inflammatory drugs - Drugs that kill or suppress T cells (*azathioprine or methotrexate*) - *IVIg* (intravenous immunoglobulin) - Plasmaphoresis - *Anti-cytokines* (Enbrel, Remicade, Humira which neutralize TNFa) - *Anti-CD20* (rituxamab to kill B cells which are making autoantibodies) - Bone marrow transplants
SLE: Homogenous IF Staining
- Antigen is present throughout the nucleus - intense staining
Sjögren Syndrome - Antibodies
- Autoantibodies to *SS-A (Ro), SS-B (La)* ribonucleoprotein ags -= ANAs (90%, not entirely specific) - Association with more severe and systemic disease and high anti SS-A - *Rheumatoid factor (Ab to self IgG)* present even in absence of RA - Initial polyclonal B cell proliferation induced by helper Ts - Genetic factors: Inheritance of certain MHC II molecules, *Loss of tolerance of CD4+ T cells*
General features of autoimmune diseases
- Chronic and progressive: *epitope spreading* due to release of new self antigens after tissue damage - Clinical manifestations determined by nature of underlying immune response: primarily antibody or T-cell mediated/both. - Organ specific vs. systemic/collagen vascular
Mixed Connective Tissue Disease
- Clinical features that are a *mixture of SLE, systemic sclerosis, polymyositis* - Sometimes evolve into classic SLE or scleroderma over time - *High anti-U1 ribonucleoprotein titers* (another ANA) - Typically present with synovitis of fingers, Raynaud's, mild myositis
LE cell (histo) - SLE
- DNA material that has complexed w/ nuclear antibodies
Central tolerance
- Deletion of self reactive T and B cells during development - Thymus- negative selection by apoptosis of T cell expressing receptor for autologous antigens - Bone marrow- deletion of self reactive B cells by apoptosis - *Slippage* occurs: because not all self antigens are present in thymus or bone marrow, so some self-reactive cells will get through!
SLE Morphology
- Deposition of immune complexes (*inflammation at high pressure sites*) - Acute necrotizing vasculitis; Chronic stages with fibrosis and luminal narrowing - *Kidney glomeruli*: spectrum of changes: class I - VI
Clinical Course in SLE
- Difficult to diagnose in many cases - Course variable - Benign, indolent - Malignant, rapid - Remissions and relapses - Rx steroids/ immunosuppressive - 90% 5 year survival - 80% 10 year survival
Sjögren Syndrome (type IV) - most common + least understood type!
- Dry eyes (keratoconjunctivitis sicca) - Dry mouth (xerostomia) - T-cell immune mediated destruction of lacrimal and salivary glands (*ductal epithelial cells* are primary target) - Primary/isolated form - *sicca syndrome* - Secondary form - associated with other autoimmune disorder (RA, SLE, polymyositis, systemic sclerosis, vasculitis or thyroiditis in 60% of patients)
The effect of hormones on autoimmunity
- Females are overwhelmingly predisposed to autoimmune diseases compared to men - Difference in hormones a contributing factor?
SLE: CNS
- Focal neurological deficit or neuropsychiatric symptoms - *Intimal proliferation in small vessels* due to antiphospholipid Abs; anti-synaptic membrane protein Abs have been found - can also get vasculitis in CNS
SLE (kidney, class IV)
- Focal segmental GN with necrotic tuft (thin arrow), epithelial crescent (thick arrow) and tuft adherent to Bowman's capsule (double arrow)
HLA and autoimmunity
- HLA genes have strong correlation to autoimmunity - 2 maternal and 2 paternal haplotypes inherited - Siblings - 50% share one haplotype, 25% will share both haplotypes, and 25% will share 0 haplotype - heterozygotes: certain HLA alleles are not risk factors by themselves but only become risk factors when matched with certain other HLA alleles - *DQ2/DQ8 heterozygotes* more susceptible to *type I diabetes* than DQ2 or DQ8 homozygotes - Why HLA (MHC)? - variability in MHC translates to *variability in types of peptides that can be presented* to lymphocytes (foreign + self)
Genetic factors
- Inherited deficiencies (AIRE, FoxP3) - HLA bias - HLA allotype combinations - Relatives of patients have higher risk - Other genes
Sjogren syndrome
- Intense lymphocytic and plasma cell infiltration with ductal epithelial hyperplasia in a salivary gland - centered around ducts!
SLE: LE
- LE bodies or *hematoxylin bodies* in tissue: ANAs binding to exposed cell nuclei/DNA and become homogenous (*smudgy*) - LE cell in vitro: phagocytic leukocyte that has engulfed denatured nucleus of damaged cell, cross reactive, smudgy
Generation of T cell responses against self antigen
- Lack of appropriate control mechanisms cause *autoantigen to be presented on MHC to cognate T cells* - T cells become activated, proliferate, *migrate to sites where self antigen is found* - CD4+ T cells release mediators (class switching or inflammation; depends on antigen) that lead to tissue destruction - More autoantigens are released and presented for T cell reactivation *(positive feedback loop)*
Sjögren Syndrome- morphology
- Lacrimal, salivary and other secretory glands involved - Intense lymphocyte and plasma cell infiltrates w/ germinal center formation - *Loss of normal architecture* - Mucosal atrophy, fibrosis - Ulceration of conjunctiva, oral mucosa + nasal septum (b/c no longer getting salivary secretions / tears! which are protective) - 25% have involvement of CNS, skin, kidneys, muscle - Kidney involvement usually *mild interstitial nephritis: glomerular lesions rare* (unlike SLE, which is glomerular in nature) - Synovitis, pulmonary fibrosis, peripheral neuropathy
Infection in autoimmunity
- May up-regulate expression of co stimulators on APCs; if APCs accidentally present self antigen, *anergy may fail* - Some microbes express antigens that have same AA sequence as self antigens: *molecular mimicry* (Rheumatic heart disease) - *Epstein Barr virus* --> similar to myelin basic peptide (self) --> MS - *HLA-DR2*
Sjögren Syndrome: stats
- Most common in women between 50-60 years of age (older than in Lupus) - Enlargement of salivary glands - Present with dry mouth and lack of tears - 40 fold increased risk of developing a *non-Hodgkin B cell lymphoma marginal zone lymphoma (MALT)*
Systemic Sclerosis- Clinical course
- Nearly all develop *Raynaud 's phenomenon* (intense pain in fingers/toes in cold weather) - Hands atrophy and become immobile - Dysphagia from esophageal involvement - Dyspnea and chronic cough - Pulmonary HTN with *cor pulmonale (right sided heart failure)* - Renal failure may lead to *malignant HTN* - Most progress slowly and steadily downhill over many years - Life span *normal if no renal involvement* - 10 year survival is 35 - 70% - CREST has much better prognosis: Begins frequently with Raynaud's phenomenon with face and hand involvement only for many years
Breakdown of peripheral tolerance
- Normally when autoreactive T cells entering periphery interact with self antigen presented on MHC but *lack of CD28/B7 costimulation* --> anergy - *CTLA-4 (negative regulator)* also competes for costimulation activity and helps balance T responses - Changes to *CD80/86 and CTLA-4* alleles can disrupt this balance --> autoimmunity - *Fas* pathway mutations: *ALPS (autoimmune lymphoproliferative syndrome)* high IgG, LAD
Autoimmunity Diagnosis
- Patient history and appearance (SLE, RA, psoriasis) - Organ-specific autoimmunity - tissue examination for antibody:antigen interactions - Serum tests for autoantibodies in vitro - Systemic autoimmune disease: *increases in IgG, immune complexes, and C3 levels* - Autoantibodies may be present up to *10 years before development of disease*
SLE: Heart
- Pericarditis - Myocarditis - *Libman-Sacks/valvular endocarditis* - Coronary artery disease; accelerated; antiphospholipid antibodies cause endothelial damage - Hypertension (multifactorial, partially due to kidney disease) - can see olibteration of coronary artery! (pic)
Inflammatory Myopathies
- Rare disorders with *immune mediated muscle injury* and inflammation which occur alone or with other disorder such as Systemic sclerosis 1) Polymyositis 2) Dermatomyositis - Women have increased risk of developing visceral cancers (lung, ovary, stomach) 3) Inclusion body myositis
Environmental factors contributing to autoimmune disease development
- Smoking - increased susceptibility to certain diseases like arthritis - Drugs - haptens or mutating agents that may alter self antigens - Exposure to chemicals - Physical trauma - access to immune privileged sites - Hygiene hypothesis - like allergies, the incidence of autoimmune disease increases with industrial development and economic status - Gut microbes, vitamin D deficiency
HLA and type I diabetes
- Suggests that the trend related to the development of type I diabetes relies on type of HLA - siblings most likely develop share 2 haplotype > 1 haplotype > 0 haplotypes
Systemic Lupus Erythematosus (SLE)
- Systemic disorder primarily affecting skin, kidneys, serosal membranes, joints, heart - Vast array of autoAbs including *antinuclear antibodies (ANA), antiphospholipid Abs + against RBCs, WBCs, platelets* - 1: 2500 (1:700 in childbearing age) - 1:245 in African American women - Usually presents in second or third decade - 9:1 female to male
The effect of hormones on autoimmunity!
- Testosterone = anti-inflammatory - prolactin may be pro-inflammatory - estrogen has been shown to have both pro- and anti- properties - Autoimmune disease development and symptoms change with pregnancy and menopause (hormone levels are changing) - Adrenal hormones (partially different expression in male versus females) have also been proposed to contribute
poison ivy
- Type IV hypersensitivity - hapten interacts w/ host surface + IC carriers to form new antigens - CD4 + CD8 T cells are activated - epidermal cells are destroyed
SLE: Rim IF Pattern
- accentuated along nuclear membrane - speckled = dots, nucleolar = blob in center - *anti dsDNA*
Antinuclear antibodies (ANA) in SLE
- against any molecules present in nucleus! - defect in self-tolerance - Anti DNA - Anti histone - Anti *nonhistone proteins bound to RNA* - Anti nucleolar antigens
Violet Hematoxylin Bodies in Necrotic Areas (H&E, SLE)
- amorphous purple stuff - damaged nuclear material that has complexed with Abs
Systemic Sclerosis
- atrophy of dermal glands - complete vaso-occlusion of artery
Transfer of autoimmunity
- can be transferred due to ability of IgG to cross placenta - Symptoms are transient, treatable (infant may not develop disease)
Multi System Immune Disorders
- collagen vascular or CT diseases (SLE, RA, scleroderma) - soft tissue, joints, etc.
Molecular mimicry - acute (pic)
- cross-reactive B cells involved, NOT T cells
IF Pattern in Skin Biopsy in SLE
- deposition at dermal/epidermal junction - can't see epidermis on right!
Vasectomy
- exposing immune privilege sites to cells - can result in autoimmunity
CTLA-4
- expressed on all activated T cells - mechanism to dampen T cell response
Inclusion Body Myositis
- hollow inclusions within skeletal muscle fibers
Epitope spreading
- immunodominant epitopes of a protein recognized by autoantibodies spread to new epitopes of the same or different proteins - makes antigen-specific cells difficult to target - may result in *presentation of new antigens that were not part of negative selection* - can originate from a pathogen epitope recognized in a previous infection
Pemphigus
- in presymptomatic stage! - starts w/ EC5, by the time the disease happens it's at level of EC1
Pathogen-induced changes
- induction of MHC class II on cells normally lacking (professional antigen presenting cells: macrophage, DC, B cell) - Infections can trigger certain signals (*IFNg*) that cause *MHC class II upregulation* - Autoreactive T cells then have more access to antigens due to increase in # of APCs - these antigens could be more diverse + tissue-specific compared to what is presented in thymus during development
Systemic Sclerosis (fingers)
- initial signs - sausage fingers - becomes more fibrotic --> clawlike deformity
Self tolerance
- lack of responsiveness to one own antigens 1) Central tolerance (thymus + bone marrow) 2) Peripheral tolerance (anergy, Treg suppression, apoptosis)
Renal Microscopic changes in SLE
- left: looks normal! can't see Abs - right: wire loops = vascular involvement, hematoxlin body (nuclear stuff)
Kidney in SLE (gross specimen)
- mottled, hemorrhagic appearance - foci of hemorrhage around capsule, congested
SLE (CNS pics)
- non-specific finding due to infarct - little hemorrhagic dots from vasculitis
Immune privilege
- peripheral mechanism - certain tissues (*CNS, eye, testis*) have barriers that prevent leukocyte entry as a protective measure against inflammation - In some autoimmune disorders these barriers are broken (by trauma or infection), autoreactive T cells are able to cause chronic inflammation!
Thymus schematic
- remember: mechanism is apoptosis
Libman Sachs endocarditis (SLE - heart)
- small vegetations near valve - infective endocarditis lesions larger
Systemic Sclerosis Symptoms
- starts in fingers, moves proximally: edema --> claw - GI barrets/ malabsorption - damage to *kidney arteries* - HTN-like disease
AIRE
- transcription factor (autoimmune regulator) in medulla epithelium - responsible for inducing *presentation of self antigens during neg selection in thymus* - mutations --> autoimmune polyendocrine syndrome *ALPS* (parathyroid, adrenals) chronic candida infections - Multi-organ autoimmune disease (B and T cell mediated) termed APECED
Skin Biopsy in SLE
- vacuolar degeneration at dermal/epidermal junction - mononuclear cell infiltrate
Molecular mimicry - acute
- when adaptive immune response generates *pathogen-specific response to antigens similar to self antigens* (throat infection with certain Streptococcus sp.) - Ab generated against strep are also reactive against antigens in heart, joints, and kidneys - These Abs *fix complement (type II)* --> widespread inflammation (rheumatic fever; joint pain, CV difficulties) - autoimmune disorder is *transient* b/c is *no autoreactive T cell component* - positive feedback loop needed for generation of additional Ab is absent!
allergy versus autoimmunity
- you can avoid penicillin, horse serum, and poison ivy - but you cannot rid yourself of RBCs, nucleic acids, or myelin! - This is why autoimmune diseases are generally incurable and treatment options are mostly just targeting symptoms
Immunologic tolerance
-unresponsiveness to an antigen induced by exposure of lymphocytes to that antigen
SLE Patterns of Immunofluorescence
1) *Homogeneous* or diffuse - Chromatin, histones and DS DNA antibodies 2) *Rim* or peripheral - Double stranded DNA (DS DNA) antibodies 3) *Speckled - Most common, least specific*, histones and ribonucleoprotein antibodies 4) *Nucleolar* - Nucleolar RNA antibodies - not specific for SLE! Can be seen in other CT disorders
Peripheral Tolerance
1) Anergy: Lymphocytes that recognize self antigens rendered *functionally unresponsive*: CD28, CTLA-4, and PD-1 receptors 2) Peripheral suppression by Treg cells (CD25 + FoxP3*) - Excrete immunosuppressive cytokines *IL-10 and TGF-β* - Prevent immune reaction against *fetal antigens* 3) Deletion by apoptosis: *FAS-mediated*
SLE - blood antibodies
1) Antibodies to RBC's WBC's and platelets 2) Antiphospholipid antibodies in 30-40% of patients - *False positive syphilis serology* - *Lupus anticoagulant /antiphospholipid Ab* syndrome (falsely elevated PTT, but also develop thrombosis)
Graves' disease diagnosis + treatment
1) Diagnosis: Symptoms of altered metabolism (weight loss, palpitation) and bulging eyes - *Elevated T3 + T4, low TSH* - Circulating *Abs to TSH receptor, TH2 dependent* response 2) Treatment - *Radioactive iodine* to specifically destroy thyroid gland + halt excess production - followed by *lifelong thyroid replacement therapy* - Pregnancy or other complications: some drugs and transiently disrupt T3 and T4 production along with medications to control heart rate
Scleroderma major categories
1) Diffuse scleroderma (Scl-70 + anti RNA pol III) - Symmetric widespread skin fibrosis, with *rapid progression and early visceral involvement* 2) Limited scleroderma (anti-centromere Abs) - *CREST syndrome* = Calcinosis, Raynaud's, Esophageal dysmotility, Sclerodactyly, Telangiectasia 3) Overlap syndromes - Either diffuse or limited scleroderma with typical features of one or more other autoimmune disease like MCTD
Moar SLE
1) Environmental factors - Drug induced lupus (*hydralazine, procainamide, penacillamine*) - Sex hormones: gender specific - UV exposure 2) Immunologic factors - CD4+ T cell as effector cell - Type 1 interferon - B-cell intolerance 3) Mechanisms of tissue injury - Autoantibodies as mediator - Visceral injury by type III hypersensitivity - RBC, WBC, and platelet injury by type II hypersensitivity
Genetic factors in autoimmunity
1) Familial clustering - Greater occurrence in monozygotic vs. dizygotic twins 2) Linkage with HLA antigens - Especially class II alleles (HLA-DR, HLA -DQ) - Polymorphisms in *PTPN22* associated with RA, type 1 DM, others - *NOD2 - Crohn's disease* - *IL-2, IL-7 receptors: MS* and others
Autoimmune thyroiditis
1) Grave's Disease - hyperthyroidism - *Type II non-cytotoxic* hypersensitivity 2) Hashimoto's thyroiditis (chronic thyroiditis) - hypothyroidism - *Type IV cytotoxic* hypersensitivity
Pathogens + Autoimmunity
1) Molecular mimicry 2) Inducing expression of self molecules not normally presented on a certain cell type 3) activation of anergized or silenced autoreactive T cells! - Since both B cell and T cell-mediated autoimmunity rely on T cell help, chronic + non-inherited disorders are *rooted in a previous infection that resulted in inflammation + clonal expansion of autoreactive T cells!*
Major Causes of Death in SLE
1) Renal failure 2) Intercurrent infections (even though immune system is hyperstimulated, it's not working properly) 3) Diffuse CNS involvement
SLE: Skin+ joints
1) Skin - *Malar rash* - Liquifactive degeneration of *basal layer* (due to complex deposition) - Immune complexes and complement at *dermal- epidermal junction* 2) Joints involved frequently - Swelling with mononuclear cell infiltrate without destruction; *non erosive synovitis* (unlike RA)
SLE: Spleen/serosa
1) Splenomegaly with follicular hyperplasia - *Onion skin lesions - plasma cells in red pulp* (usually not in red pulp!) 2) Serosal membranes - Pericardium and pleura - Serous effusions - Fibrinous exudates - Fibrous obliteration of space - left: white dots = onion appearance of white pulp
IgG4-related disease
1) infiltration of tissues by *IgG4-secreting plasma cells* 2) *storifrom fibrosis, obliterative phlebitis* 3) increased serum IgG4 - More common in *middle aged men* - Respond to *steroids* - *pancreas* often involved - plasma cells around pancreatic duct, do special stain for IgG4 plasma cells
How does an autoimmune disease develop?
1. Break of central tolerance 2. Break of peripheral tolerance 3. Generation of an immune response against self antigen 4. Effector cells and memory cells reactivate 5. chronic inflammation occurs 6. resulting in clinical symptoms
