DEVELOPMENT OF AUTOIMMUNITY ARPAD LANYI PhD

CENTRAL AND PERIPHERAL TOLERANCE TO SELF ANTIGENS Central tolerance: Elimination of self-reactive clones. BUT!!! Some clones escape. Peripheral tolerance: Elimination of „fugitive” or altered clones is an important role for regulatory T-cells. Central and peripheral tolerance to self antigens. Central tolerance: Immature lymphocytes specific for self antigens may encounter these antigens in the generative (central) lymphoid organs and are deleted; B lymphocytes change their specificity (receptor editing); and some T lymphocytes develop into regulatory T-cells. Some self-reactive lymphocytes may complete their maturation and enter peripheral tissues. Peripheral tolerance: Mature self-reactive lymphocytes may be inactivated or deleted by encounter with self antigens in peripheral tissues, or suppressed by regulatory T-cells.

IMMUNE RESPONSES ARE NOT INITIATED IN THE PERIPHERY Normal tissue cells do not express MHC class II NO SIGNAL 1. for CD4+ Th activation Normal tissue cells do not express co-stimulatory molecules and do not produce T-cell differentiating cytokines NO SIGNAL 2. for CD4+ Th activation Migration of naive T lymphocytes to normal tissues is limited Antigen presenting cells are not activated in normal tissues UNDER NORMAL CIRCUMSTANCES PERIPHERAL TISSUES ARE PROTECTED FROM IMMUNE RESPONSE

GENERAL FEATURES OF AUTOIMMUNE DISORDERS Autoimmune diseases may be either systemic or organ specific, depending on the distribution of the autoantigens that are recognized. Circulating immune complexes – SLE Autoantibodies or T-cell responses against self antigens with restricted tissue distribution - Type 1 diabetes Various effector mechanisms are responsible for tissue injury in different autoimmune diseases. Autoantibodies Immune complexes Autoreactive T lymphocytes All autoimmune diseases involve breaking T-cell tolerance.

AUTOANTIBODY PRODUCTION IS DEPENDENT ON THE AVAILABILITY OF AUTOREACTIVE T-CELLS Practically all autoimmune diseases involve some T-cell defects In the absence of T-cell help autoreactive B-cells are retained in the T-cell zone and die by apoptosis Arrest and death of autoreactive B cells in secondary lymphoid tissue in the absence of autoantigen specific T-cells. B-cells enter the T-cell zone of a lymph node through high endothelial venules (HEVs). B-cells with reactivity for foreign antigens (non-autoreactive) are shown in yellow, and autoreactive cells in gray. Non-autoreactive B-cells enter the lymphoid follicle and receive signals to survive. If autoreactive B-cells encounter their specific antigen they stop in the T-cell zone. Because there are no cognate T-cells specific for the autoantigen, the autoreactive cells cannot leave the T-cell zone to enter the primary follicle. The autoreactive B-cells thus fail to receive survival signals and undergo apoptosis in situ in the T-cell zone.

SINGLE GENE MUTATIONS CAUSE AUTOIMMUNITY AIRE - Failure of central tolerance - APECED

AUTOIMMUN REGULATOR (AIRE) A transcription factor expressed by thymic medullary epithelial cells and induces expression of many tissue-specific genes Deficiency in establishing central T-cell tolerance allows too many self reactive T-cell clones to leave the thymus AUTOIMMUNE POLYENDOCRINOPATHY- CANDIDIASIS-ECTODERMAL DYSTROPHY (APECED) Rare disease, but more frequently seen in inbred populations Finnish, Iranian Jews and in the island of Sardine

SYMPTOMS OF APECED Anti-Th17 specific antibodies!!!!! Role of Th17 discovered by studying a rare immunodeficiency https:///jimneydandme.wordp ress.com/james-story APECED was the first systemic (bodywide) autoimmune disease found due to a defect in a single gene.

SINGLE GENE MUTATIONS CAUSE AUTOIMMUNITY AIRE - Failure of central tolerance - APECED FOXP3 – Deficiency of functional regulatory T cells - IPEX CTLA4 - Failure of anergy in CD4+ T cells; defective function of regulatory T cells - several autoimmune disorders CD25 - Defective development, survival, or function of regulatory T-cells – IPEX-like C4 - Defective clearance of immune complexes; failure of B cell tolerance – SLE FAS/FASL - Defective deletion of anergic self-reactive B cells; reduced deletion of mature CD4+T cells - Autoimmune lymphoproliferative syndrome (ALPS) These genes are associated with rare autoimmune diseases, their identification has provided valuable information about the importance of various molecular pathways in the maintenance of self-tolerance.

MOST AUTOIMMUNE DISEASES ARE COMPLEX POLYGENIC TRAITS MULTIPLE INHERITED GENETIC POLYMORPHISMS CONTRIBUTE TO DISEASE SUSCEPTIBILITY

HLA IS THE DOMINANT GENETIC FACTOR AFFECTING SUSCEPTIBILITY TO AUTOIMMUNE DISEASE Family studies reveal that HLA type correlates with susceptibility to type 1 diabetes Haplotype is a group of genes within an organism that was inherited together from a single parent Family studies reveal that HLA type correlates with susceptibility to type 1 diabetes. The top panel shows the frequency with which two siblings share HLA haplotypes in the population as a whole. The percentages are those expected from a simple Mendelian segregation of the two maternal and two paternal HLA haplotypes. In the bottom panel the analysis has been confined to pairs of siblings who both have type 1 diabetes. In these sibling pairs, the frequency distribution of HLA haplotypes differs greatly from that expected from simple Mendelian segregation. Pairs of siblings with the disease are much more likely to have the same HLA type than are pairs of siblings who are healthy. Similar results are seen for many autoimmune diseases

ASSOCIATIONS OF HLA ALLOTYPES WITH AUTOIMMUNE DISEASE HLA associations reflect the importance of T-cell tolerance in preventing autoimmunity Many more autoimmune diseases are associated with HLA II than with HLA I indicating that CD4+T-cells are inherently more likely to lose tolerance to a self antigen than are CD8+T-cells Associations of HLA allotypes with autoimmune disease. The data are derived from the Norwegian population. In the column ‘Relative risk,’ numbers greater than 1 indicate that the HLA allotype confers increased susceptibility relative to the general population; numbers less than 1 indicate increased protection.

PREFERENTIAL ALLELE ASSOCIATIONS: LINKAGE DISEQUILIBRIUM Particular alleles of the different polymorphic genes are combined in HLA haplotypes at frequencies higher than expected by chance A1–B8–DR3–DQ2 haplotype, which includes alleles for HLA-A, -B, -C, -DR, and -DQ is characteristic of Caucasian populations (up to 11%). Association with several common autoimmune diseases: type 1 diabetes, SLE, myasthenia gravis, autoimmune hepatitis, primary biliary cirrhosis. Key genes of the A1–B8–DR3–DQ2 HLA haplotype.

COMBINATIONS OF HLA CLASS II SUSCEPTIBILITY TO TYPE 1 DIABETES ALLOTYPES CONFER SUSCEPTIBILITY TO TYPE 1 DIABETES Common Caucasian HLA haplotypes that encode either the DQ2 or the DQ8 allotype confer susceptibility to type 1 diabetes. Heterozygous individuals are more susceptible to diabetes. This augmented susceptibility is due to a novel HLA-DQ heterodimer consisting of the DQ8 α-chain and the DQ2 β-chain. Certain HLA heterozygous individuals are more susceptible to diabetes than homozygous individuals. The person shown here has two HLA haplotypes that are independently associated with susceptibility to type 1 diabetes. The DR3 haplotype contains DQ genes that encode the DQα*05:01 chain and the DQβ*02:01 chain; the DR4 haplotype contains genes that encode the DQα*03 chain and the DQβ*03:02 chain. The two α chains and two β chains made in this person’s cells can associate in different combinations to form four different DQ isoforms, of which three (those shown in the figure) are associated with susceptibility to diabetes. The DQ heterodimer associated with the highest susceptibility is that comprising the DQα*03 chain made from the DR4 haplotype and the DQβ*02:01 chain made from the DR3 haplotype. This heterodimer can be made only in DR3/DR4 heterozygous individuals, whereas the two heterodimers with weaker disease association are also made in homozygous individuals: heterodimers of the DQα*05:01 and DQβ*02:01 chains (called the DQ2 molecule) in DR3 haplotype homozygotes and heterodimers of the DQα*03 and DQβ*03:02 chains (called the DQ8 molecule) in DR4 haplotype homozygotes. The heterozygote is therefore more susceptible to disease than either homozygote. As a general rule, heterozygosity gives increased fitness over homozygosity, but in this situation the reverse is true.

POLYMORPHISMS IN NON-HLA GENES ASSOCIATED WITH AUTOIMMUNITY Many of the polymorphisms associated with various autoimmune diseases are in genes that influence the development and regulation of immune responses. These are examples only to demonstrate that poloimorphisms in many immunoregulatory genes may contribute to autoimmunity.

GENETIC PREDISPOSITION IS NOT EQUAL TO AUTOIMMUNE DISEASE INDIVIDUALS WITH GENETIC PREDISPOSITION DEVELOP AUTOIMMUNE DISEASE WITH A MAXIMUM FREQUENCY OF 20% ENVIRONMENTAL FACTORS PLAY A ROLE IN DEVELOPING OF AUTOIMMUNITY

DRUG INDUCED HEMOLYTIC ANEMIA Alpha methyldopa therapy results in the formation of red blood cell autoantibodies in 10-20% of patients taking the drug for longer than 4 months. True autoantibodies: directed against an autoantigen on the red blood cell membrane, not against the drug  The target membrane antigen is usually within the Rhesus system Drug-dependent Abs Penicillin, cefotetan: covalently bind to rbc membrane proteins. Anti-drug Ab (usually IgG) - attaches to the drug-coated RBCs - clearance by macrophages Ceftriaxone: binds non-specifically to RBC membrane proteins Abs are formed to the combined membrane-drug (hapten) complex, can be IgM or IgG, and often activate complement - acute rapid intravascular hemolysis

SMOKING Smoking damages the mucosa of the airways and exacerbates many diseases. All patients with Goodpasture’s syndrome develop glomerulonephritis, but only those who habitually smoke cigarettes develop pulmonary hemorrhage. In nonsmokers, the basement membranes of lung alveoli are inaccessible to antibodies. In smokers the lack of integrity gives circulating antibodies access to the basement membranes.

PHYSICAL TRAUMA Physical trauma to one eye initiates autoimmunity that can destroy vision in both eyes.

ENVIRONMENTAL FACTORS INFECTIONS: ENVIRONMENTAL FACTORS THAT CAN TRIGGER AUTOIMMUNE DISEASE

ROLE OF INFECTIONS IN THE DEVELOPMENT MOLECULAR MIMICRY MAY LEAD TO OF AUTOIMMUNITY MOLECULAR MIMICRY MAY LEAD TO SEVERE AUTOIMMUNE REACTIONS Left: A, Normally, encounter of a mature self-reactive T cell with a self antigen presented by a costimulator-deficient resting tissue antigen-presenting cell (APC) results in peripheral tolerance by anergy. (Other possible mechanisms of self-tolerance are not shown.) B, Microbes may activate the APCs to express costimulators, and when these APCs present self antigens, the self-reactive T cells are activated rather than rendered tolerant. C, Some microbial antigens may cross-react with self antigens (molecular mimicry). Therefore, immune responses initiated by the microbes may activate T cells specific for self antigens. Right: Autoimmunity may be caused by self peptides that mimic pathogen-derived peptides and stimulate a T-cell response. The first panel shows the same MHC molecule presenting two different peptides: one from the pathogen, and a self peptide that mimics it. The second panel shows a naive CD4 T cell being activated by the pathogen peptide. This activated CD4 TH1 cell can then activate a macrophage presenting the self-peptide mimic, as shown in the third panel, thus initiating an inflammatory reaction.

INFECTIONS ASSOCIATED WITH THE START OF AUTOIMMUNITY

ANTIBODIES AGAINST STREPTOCOCCAL CELL-WALL ANTIGENS CROSS-REACT WITH ANTIGENS ON HEART TISSUE Antibodies against streptococcal cell-wall antigens cross-react with antigens on heart tissue. The immune response to the bacteria produces antibodies against various epitopes of the bacterial cell surface. Some of these antibodies (yellow) cross-react with the heart, whereas others (blue) do not. An epitope in the heart (orange) is structurally similar, but not identical, to a bacterial epitope (red).

INDUCTION OF HLA CLASS II EXPRESSION FACILITATES AUTOIMMUNITY In response to IFN-γ MHCII expression is induced on thyroid cells (on the β cells of the pancreas as well as on microglia). Insufficient for the activation of naive T-cells (not normally present in the periphery anyway), BUT effector T-cells cross-reacting with autoantigens may be activated. INDUCTION OF HLA CLASS II EXPRESSION ON TISSUE CELLS FACILITATES AUTOIMMUNITY Induction of HLA class II expression on tissue cells facilitates autoimmunity. Thyroid epithelial cells do not normally express HLA class II molecules (top panel). They are induced to do so by IFN-y (center panel). They are then able to present thyroid peptides to activated antigen-specific T-cells, which induces autoimmune thyroid disease (bottom panel). IFN-y produced by activated T-cells feeds back to amplify HLA expression and antigen presentation.

GENETIC AND ENVIRONMENTAL FACTORS ACT TOGETHER TO CAUSE AUTOIMMUNITY

RHEUMATOID ARTHRITIS IS INFLUENCED BY GENETIC AND ENVIRONMENTAL FACTORS Smoking, HLA-DR4 and an immune response to citrullinated proteins are all tied together in the same disease- causing mechanism Smoking is the major environmental factor associated with rheumatoid arthritis ACPA+: strong association with HLA- DR4 and smoking APCA-: no association smokers nonsmokers STARTING FROM LEFT: In tissues stressed by wounds, infection or cigarette smoke, peptidyl arginine deiminase (PAD) activity is induced. By converting arginine residues to citrulline, PAD destabilizes proteins and makes them more susceptible to degradation. It also introduces novel B-cell and T-cell epitopes into tissue proteins that can stimulate an autoimmune response. With the exception of DRB1*04:02, all the DRB1*04 alleles shown are associated with susceptibility to rheumatoid arthritis. What distinguishes the DRβ*04:02 chain from those encoded by the other alleles is a cluster of amino acid substitutions at positions 67, 70, and 71. These substitutions change the localized charge environment within the peptide-binding groove by removing a basic (positively charged) residue (shown in blue) and inserting two acidic (negatively charged) residues (shown in red). Tobacco smoking may lead to citrullination of proteins within the lungs. In individuals with at least one copy of the HLA-DRβ SE, production of autoantibodies directed against citrullinated proteins can occur. ACPAs alone are not sufficient to cause RA—a second trigger is required (such as an infection or breast feeding) which, in individuals with the SE, can lead to RA. Abbreviations: ACPAs, anti-citrullinated protein antibodies; SE, shared epitope; RA, rheumatoid arthritis. The relative risk of developing rheumatoid arthritis in which no autoimmune response to citrullinated protein antigens (ACPA) is made does not correlate with the presence of HLA-DRB1*04 ‘susceptibility’ alleles or with smoking. The red columns indicate smokers, the blue columns nonsmokers. The number above each column is the relative risk of disease for that group. In contrast the relative risk of developing rheumatoid arthritis in which an autoimmune response to ACPA has been made is increased by the presence of HLA-DRB1*04 susceptibility alleles and by smoking. At highest risk are smokers who have any two HLA-DRB1*04 susceptibility alleles. These data are from a cohort of Swedish patients with rheumatoid arthritis. Data courtesy of Lars Klareskog. Basic residues in the peptide-binding groove of the DRβ*04 chain are necessary to confer susceptibility to rheumatoid arthritis

INTERPLAY BETWEEN GENETIC AND ENVIRONMENTAL FACTORS: CELIAC DISEASE Strong genetic predisposition: DQ2, DQ8 allotypes – celiac disease - 80% DQ2 (the same DQ allotypes that predispose to type 1 diabetes) Caucasian populations bread: staple DQ2:30% Celiac disease: 0.5-1% The concordance rate in monozygotic twins: 75-80% Environmental factors: Antibodies, memory T-cells – cross-reaction Repeated infections with rotavirus IFN-γ therapy (hepatitis) Gluten introduction – maternal IgA Comparison of genotypes and risk for celiac disease. Shown here are how various combinations of two DQα chains and two DQβ chains give genotypes with a range of relative risk for celiac disease.

ROLE OF THE GUT MICROBIOTA IN AUTOIMMUNITY Left: Segmented filamentous bacteria (SFB) colonization induces T helper 17 (TH17) cell development in the intestine. These TH17 cells might migrate to the periphery to affect systemic and central nervous system (CNS) immunity; increased intestinal TH17 cells enhance the expansion of pathogenic autoantigen-specific T cells in the intestine and cause inflammation in the CNS. By contrast, 'beneficial' commensal bacteria can attenuate CNS inflammation through the induction of forkhead box P3 (FOXP3)+ regulatory T (TReg) cells. Induced TH17 cells can also promote autoimmune arthritis by facilitating autoantibody production by B cells (not shown). In addition, microbiota-induced interleukin-1β (IL-1β) signalling participates in the development of rheumatoid arthritis through the induction of TH17 cells. The IL-1 receptor (IL-1R) antagonist blocks IL-1β signalling and abrogates joint inflammation. Balance in the microbial community also determines susceptibility to type 1 diabetes. A decreased Firmicutes/Bacteroidetes ratio as a result of a deficiency in myeloid differentiation primary-response protein 88 (MYD88) in non-obese diabetic mice is associated with an attenuated risk of type 1 diabetes. SFB-induced TH17 cells protect the host against type 1 diabetes development by an unknown mechanism. Finally, exposure to microorganisms in neonatal, but not adult, life decreases the accumulation of invariant natural killer T (iNKT) cells in the gut, which results in protection against allergic inflammation in the lungs. In addition, microbial compounds stimulate peripheral B-cells through B-cell-intrinsic MYD88 signalling and inhibit IgE production. Decreased levels of peripheral IgE result in decreased numbers of basophils, and attenuate the risk of allergic airway inflammation. EAE, experimental autoimmune encephalomyelitis. Right: During homeostasis, the gut microbiota has important roles in the development of intestinal immunity. Beneficial subsets of commensal bacteria tend to have anti-inflammatory activities. Pathobionts that are colitogenic are directly suppressed by beneficial commensal bacteria partly through the induction of regulatory immune responses, involving regulatory T (TReg) cells, interleukin-10 (IL-10) and regenerating islet-derived protein 3γ (REGIIIγ). In inflammatory bowel disease (IBD) a combination of genetic factors (for example, mutations in nucleotide-binding oligomerization domain 2 (Nod2), autophagy-related gene 16-like 1 (Atg16l1) and interleukin-23 receptor (Il23r)) and environmental factors (such as infection, stress and diet) result in disruption of the microbial community structure, a process termed dysbiosis. Dysbiosis results in a loss of protective bacteria and/or in the accumulation of colitogenic pathobionts, which leads to chronic inflammation involving hyperactivation of T helper 1 (TH1) and TH17 cells. Dashed line shows that that the suppression of pathobionts by beneficial bacteria is diminished. doi:10.1038/nri3430 doi:10.1038/nri3430

ROLE OF THE GUT MICROBIOTA IN AUTOIMMUNITY Right: Commensal bacteria may have a role in producing inflammatory cytokines that can worsen autoimmune disease in the joints. Gut Gram-positive bacteria, such as SFB, induce IL-1, IL-6 and IL-23 in the mucosa and also a TH17 response, increasing IL-17 and IL-22. The release of these cytokines may initiate IBD, but, when overproduced, they may spill into the systemic circulation. This may promote inflammatory diseases in distal sites, such as the joints, perhaps through action upon joint-resident lymphoid cell populations. Altered sensitivity to IL-23 may predispose people to develop rheumatic diseases, such as ankylosing spondylitis. doi:10.1038/nri3430 doi:10.1038/nm0911-1055

ROLE OF OTHER INTRINSIC FACTORS IN AUTOIMMUNITY

HORMONES Most autoimmune diseases are more prevalent in women than men. Conservative estimates indicate that nearly 80% of individuals with autoimmune diseases are women. Ankylosing spondylitis occurs more frequently in men. HORMONES Relative incidences of autoimmune disease in females and males. The numbers on the two scales give the ratio of men to women with a disease (on the left) and the ratio of women to men with a disease (on the right). PBC, primary billiary cirrhosis; CAH, chronic active hepatitis; MC-TD, mixed connective tissue disease.

SENESCENCE OF THE THYMUS AND THE T-CELL POPULATION CONTRIBUTES TO AUTOIMMUNITY T-cell populations are dynamic: T-cells must divide periodically to survive. 1% of the body’s T-cells being replaced each day. Once the thymus can no longer fulfill the demand for naive T-cells, the immune system compensates: expanding the size of existing T-cell clones altering the properties of T-cells - make them more resistant to apoptosis; CD28 - KIR Correlation between thymus involution and rheumatoid arthritis. With age there is an inverse correlation between the decreasing capacity of the thymus to make new T-cells and the increasing incidence of rheumatoid arthritis. Data courtesy of C.M. Weyand and J.J. Goronzy. RA: large clones of expanded autoreactive CD4 T-cells lack of CD28 express NK-cell receptors - KIR2DS2 produce large amounts of IFN-γ not anergic

AUTOIMMUNE DISEASES TEND TO BE CHRONIC, PROGRESSIVE AND SELF- PERPETUATING Self antigens are persistent, and once an immune response starts, many amplification mechanisms are activated that perpetuate the response Tissue injures result in the release and alterations of other tissue antigens, activation of lymphocytes specific for these other antigens, and exacerbation of the disease

MECHANISMS OF CHRONICITY OF AUTOIMMUNE DISEASES Mechanisms of chronicity of autoimmune diseases. Once an autoimmune reaction develops, amplification mechanisms (such as cytokines, shown as an illustrative example) promote activation of autoreactive lymphocytes, and release of self antigens from damaged cells and tissues leads to epitope spreading.

INTRAMOLECULAR EPITOPE SPREADING PEMPHIGUS FOLIACEUS Left: Pemphigus foliaceus is a skin blistering disease caused by autoantibodies specific for desmoglein. An adhesion molecule in the cell junctions that hold keratinocytes together, desmoglein is a cell-surface protein with five extracellular domains (EC1–EC5). The autoimmune response starts by making harmless antibodies against the EC5 domain; over time, the response can spread to make antibodies against the EC1 and EC2 domains. These antibodies cause disease and are of the IgG4 isotype. Right: How antibodies against desmoglein cause skin blistering. In the early phase of the autoimmune response to desmoglein, antibodies are made against epitopes of the EC5 domain. These epitopes are not accessible to antibody in functional membrane-associated desmoglein, but the antibodies can bind to soluble degradation products of desmoglein (left panel). Soluble immune complexes of antibody desmoglein are bound and processed by B-cells specific for epitopes of the EC1 and EC2 domains (center panel). This causes epitope spreading in the later phase of the autoimmune response and the synthesis of high-affinity IgG4antibodies specific for the EC1 and EC2 epitopes. These epitopes of membrane-associated desmoglein are accessible to antibody, which interferes with the physiological adhesive interactions of desmoglein that are necessary for maintaining skin integrity. Consequently, the antibodies cause the outer layers of the skin to separate, giving blisters (right panel).

INTERMOLECULAR EPITOPE SPREADING IN SLE In patients with SLE, an ever-broadening immune response is made against nucleoprotein antigens such as nucleosomes, which consist of histones and DNA and are released from dying and disintegrating cells. The left panel shows how the emergence of a single clone of autoreactive CD4+ T-cells can lead to a diverse B-cell response to nucleosome components. The T-cell in the center is specific for a specific peptide (red) from the linker histone H1, which is present on the surface of the nucleosome. The B- cells at the top are specific for epitopes on the surface of a nucleosome, on H1 and DNA, respectively, and thus bind and endocytose intact nucleosomes, process the constituents, and present the H1 peptide to the helper T-cell. Such B-cells will be activated to make antibodies, which in the case of the DNA-specific B-cell will be anti-DNA antibodies. The B-cell at the bottom right is specific for an epitope on histone H2, which is hidden inside the intact nucleosome and is thus inaccessible to the B-cell receptor. This B-cell does not bind the nucleosome and does not become activated by the H1-specific helper T-cell. A B-cell specific for another type of nucleoprotein particle, the ribosome (which is composed of RNA and specific ribosomal proteins), will not bind nucleosomes (bottom left) and will not be activated by the T-cell. In reality a T-cell interacts with one B-cell at a time, but different members of the same T-cell clone will interact with the B-cells of different specificity. The right panel shows the broadening of the T-cell response to the nucleosome. The H1-specific B-cell in the center has processed an intact nucleosome and is presenting a variety of nucleosomederived peptide antigens on its MHC class II molecules. This B-cell can activate a T-cell specific for any of these peptide antigens, which will include those from the internal histones H2, H3, and H4 as well as those from H1. This H1-specific B-cell will not activate T-cells specific for peptide antigens of ribosomes because ribosomes do not contain histones.

DYSFUNCTION OF REGULATORY T-CELLS

LOSS OF REGULATION OF AUTOREACTIVE T-CELLS RESULTS IN AUTOIMMUNITY ) FOXP3 deficiency: IPEX CTLA-4 haploinsufficiency: autoimmunity IL-10: severe colitis Autoimmunity can result from a loss of regulation of autoreactive T-cells. Failures of regulatory T (TReg) cell-mediated regulation include: inadequate numbers of TReg cells owing to their inadequate development, proliferation or survival; defects in TReg cell function that is intrinsic to TReg cells; and resistance of pathogenic effector T-cells to suppression by TReg cells owing to factors that are intrinsic to the effector cells or factors that are present in the inflammatory milieu and that support effector T-cell resistance. DC, dendritic cell; IL, interleukin; TGFβ, transforming growth factor-β; TH17, T helper 17. IL-6 mediated resistance in psoriasis Autoimmunity in Dry Eye: qualitative Treg defect – resistance Th17 cells doi:10.1038/nri2889

IL-6 MEDIATED RESISTANCE IN PSORIASIS IL-6 is overexpressed in lesional psoriatic skin IL-6 is necessary and sufficient for reversal of Treg suppressive function Immune cell subsets including DCs, as well as CD31+ endothelial cells, represent major sources of IL-6 in lesional psoriatic skin Average Pixel Density within Indicated Cellsa Average Pixel Density within Keratinocytesa pb Fold Increase over Keratinocytesc CD11c+ 966.5 ± 30.3 587.1 ± 30.6 0.039 1.98 ± 0.37 CD3+ 914.1 ± 35.7 676.2 ± 21.3 0.0044 1.38 ± 0.09 Mac387+ 1014.0 ± 38.4 958.9 ± 28.7 0.4056 1.08 ± 0.06 CD31+ 1495.2 ± 81.2 832.3 ± 36.3 0.0015 1.87 ± 0.23 Left: IL-6 is overexpressed in lesional psoriatic skin. Tissue sections from the indicated sources were labeled with anti-IL-6 Ab or isotype control.  Intensity of IL-6 within IL-6+ cells was calculated using MetaMorph (version 7.1) imaging software and is expressed as raw pixel density (n = 15 fields per tissue source ± SEM). Table: an = 9 fields (three fields each among three lesional psoriatic samples). bIL-6 intensity (within indicated cell type) vs IL-6 intensity within keratinocytes in the same field. cMean IL-6 intensity (within indicated cell type) relative to keratinocytes in the same field Right: IL-6 is necessary and sufficient for reversal of normal and psoriatic Treg suppressive function.  Normal or psoriatic CD4+CD25− T-cells and CD4+CD25high Treg were cocultured with the indicated concentrations of rhIL-6 and allogeneic APCs. Tritiated thymidine ([3H]) was added for the final 16 h of culture.*, p ≤ 0.01, n = 3.   10.4049/jimmunol.0803721

AUTOIMMUNITY IN DRY EYE: DEFECT IN TREGS IS QUALITATIVE NOT QUANTITATIVE Frequencies and function of Tregs. Left: Regional draining LN were harvested from normal and dry eye mice and analyzed for CD4CD25Foxp3 Treg frequency and function. Representative flow cytometric dot plots showing frequencies of Tregs. Right: Resistance of T-cells to Treg suppression. Primed T-cells isolated from the draining LN of dry eye mice were stimulated with CD3 Ab in the presence of Tregs isolated from the draining LN of normal or dry eye mice. After 3 days of coculture, cells were washed and activated with PMA plus ionomycin for 6 h in the presence of GolgiPlug. The proliferating subsets of primed T-cells were analyzed for intracellular IL-17A and IFN- by FACS. Data from a representative experiment of three performed are shown, and each group consists of four to six mice. doi: 10.4049/jimmunol.182.3.1247

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ROLE OF INFECTIONS IN THE DEVELOPMENT MOLECULAR MIMICRY MAY LEAD TO OF AUTOIMMUNITY MOLECULAR MIMICRY MAY LEAD TO SEVERE AUTOIMMUNE REACTIONS Left: A, Normally, encounter of a mature self-reactive T cell with a self antigen presented by a costimulator-deficient resting tissue antigen-presenting cell (APC) results in peripheral tolerance by anergy. (Other possible mechanisms of self-tolerance are not shown.) B, Microbes may activate the APCs to express costimulators, and when these APCs present self antigens, the self-reactive T cells are activated rather than rendered tolerant. C, Some microbial antigens may cross-react with self antigens (molecular mimicry). Therefore, immune responses initiated by the microbes may activate T cells specific for self antigens. Right: Autoimmunity may be caused by self peptides that mimic pathogen-derived peptides and stimulate a T-cell response. The first panel shows the same MHC molecule presenting two different peptides: one from the pathogen, and a self peptide that mimics it. The second panel shows a naive CD4 T cell being activated by the pathogen peptide. This activated CD4 TH1 cell can then activate a macrophage presenting the self-peptide mimic, as shown in the third panel, thus initiating an inflammatory reaction.

RHEUMATOID ARTHRITIS IS INFLUENCED BY GENETIC AND ENVIRONMENTAL FACTORS Smoking, HLA-DR4 and an immune response to citrullinated proteins are all tied together in the same disease- causing mechanism Smoking is the major environmental factor associated with rheumatoid arthritis ACPA+: strong association with HLA- DR4 and smoking APCA-: no association smokers nonsmokers STARTING FROM LEFT: In tissues stressed by wounds, infection or cigarette smoke, peptidyl arginine deiminase (PAD) activity is induced. By converting arginine residues to citrulline, PAD destabilizes proteins and makes them more susceptible to degradation. It also introduces novel B-cell and T-cell epitopes into tissue proteins that can stimulate an autoimmune response. With the exception of DRB1*04:02, all the DRB1*04 alleles shown are associated with susceptibility to rheumatoid arthritis. What distinguishes the DRβ*04:02 chain from those encoded by the other alleles is a cluster of amino acid substitutions at positions 67, 70, and 71. These substitutions change the localized charge environment within the peptide-binding groove by removing a basic (positively charged) residue (shown in blue) and inserting two acidic (negatively charged) residues (shown in red). Tobacco smoking may lead to citrullination of proteins within the lungs. In individuals with at least one copy of the HLA-DRβ SE, production of autoantibodies directed against citrullinated proteins can occur. ACPAs alone are not sufficient to cause RA—a second trigger is required (such as an infection or breast feeding) which, in individuals with the SE, can lead to RA. Abbreviations: ACPAs, anti-citrullinated protein antibodies; SE, shared epitope; RA, rheumatoid arthritis. The relative risk of developing rheumatoid arthritis in which no autoimmune response to citrullinated protein antigens (ACPA) is made does not correlate with the presence of HLA-DRB1*04 ‘susceptibility’ alleles or with smoking. The red columns indicate smokers, the blue columns nonsmokers. The number above each column is the relative risk of disease for that group. In contrast the relative risk of developing rheumatoid arthritis in which an autoimmune response to ACPA has been made is increased by the presence of HLA-DRB1*04 susceptibility alleles and by smoking. At highest risk are smokers who have any two HLA-DRB1*04 susceptibility alleles. These data are from a cohort of Swedish patients with rheumatoid arthritis. Data courtesy of Lars Klareskog. Basic residues in the peptide-binding groove of the DRβ*04 chain are necessary to confer susceptibility to rheumatoid arthritis