MICR 304 Immunology & Serology Lecture 15 Autoimmune Diseases and Transplantation Immunology Chapter 14.1 -14.5, 14.7– 14. 19; 14.22.- 37 Lecture 15 Autoimmune.

MICR 304 Immunology &

Serology

MICR 304 Immunology &

Serology

Lecture 15Autoimmune Diseases and

Transplantation ImmunologyChapter 14.1 -14.5, 14.7– 14. 19; 14.22.-

37

Lecture 15Autoimmune Diseases and

Transplantation ImmunologyChapter 14.1 -14.5, 14.7– 14. 19; 14.22.-

37

Overview of Today’s Lecture

• Horror autotoxicus• Self tolerance and breach in self

tolerance• Genetic and environmental factors

contributing to autoimmune diseases• Classification of autoimmune diseases• Selected examples for autoimmune

diseases• Transplantation immunology

Horror Autotoxicus

• Term coined by Ehrlich when he conceived the idea of antibodies

• Inherent problem of random creation of antigen receptors

• Self reacting lymphocytes are randomly and constantly generated

• Normally, autoreactive lymphocytes are either removed by apoptosis or tolerance is established

Discrimination of Self and Non-Self

Mechanism

Self antigens Non-self antigens

Timing of antigen receptor signaling

Strong signals in immature developing lymphocytes in central lymphoid organs (central tolerance)

Activation of antigen receptor in mature lymphocytes in peripheral (secondary) lymphoid organs

Antigen concentration

Continuous and high Sudden increase of previously low concentrated antigen

Co-stimulatory signals

Absent Present

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

action of a variety of mechanisms • Succession of checkpoints

PeripheralTolerance

Autoimmune Diseases

• Develop when multiple layers of self tolerance are dysfunctional

• Response to endogenous self antigen that leads to tissue damage

• Since antigen cannot be eliminated response is sustained

• Results from a combination of genetic susceptibility, break down of natural tolerance mechanisms and environmental triggers

Requirements of the Development of Autoimmune

diseases

Tolerance

Defects in Central Tolerance Development

• Defective AIRE gene– Transcription factor “autoimmune

regulator”– Allows thymic epithelial cells to

express peripheral genes– Absence leads to lack of elimination of

self reactive lymphocytes and development of severe autoimmune disease

Activation of Ignorant Lymphocytes

• Ignorance develops when self antigen is monovalent or of low affinity for antigen receptor

• Under normal circumstances, no reaction to self antigen.

• However, ignorant lymphocytes are potentially self reactive under certain circumstances:– High concentration of antigen– Immune complexes with formation of multivalence– In the context of inflammation and infection

• Co-stimulation through TLRs

When a Monovalent Selfantigen Becomes Multivalent

• Example rheumatoid factor– Anti-IgG antibodies

• Normally, B cells specific for Fc of IgG are not activated as Fc of IgG is a monovalent antigen.

• When immune complexes are formed Fc moieties of complexed IgG becomes multivalent.

• BCR of self-reactive B cells can be cross linked.

• In the presence of co-stimulatory signals self reactive B cells become activated and begin to secrete anti-IgG.

TLR Ligands Can ActivateAutoreactive B Cells

Increased liberation of host DNA during infection with

tissue damage

+ Additional co-stimulatory signals

Unmethylated CpG DNA sequences are enriched in apoptotic cells.

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

TGF• 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• Example: sympathetic ophthalmia

Sympathetic Ophthalmia

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 = infectious tolerance

• The different antigens must be presented by the same APC.

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

Etiology of Autoimmune Diseases

Environmental factors• Heterogeneous

geographic distribution of autoimmune diseases

• Triggered by infectious agents

• Trauma• Drugs• Hormones (estrogen,

progestron)

Genetic Factors• Single gene defects

described• Association with

MHC genotype– B27, DR2, DR3,

DR3/DR4

• Family and twin studies

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 apoptosis• Failure of apoptotic death of self reactive B and T lymphocytes• Autoimmune lymphoproliferative syndrome

– AIRE (autoimmune regulator gene)• Transcription factor• Regulates expression of tissue specific antigens by DC in thymus• If absent decreased expression of self antigens in thynmus• Defective negative selection of self reactive thymocytes• Autoimmune polyendocrinopathy- candidiasis-ectodermal

dystrophy

Manifestations of APECEDAutoimmune polyendocrinopathy- candidaiasis-ectodermal dystrophy

Association of HLA Serotype and Sex with Susceptibility to Autoimmune

Diseases

Hip jointsEyes

KidneysCNS

ThyroidMuscles

SystemicPancreas

Small jointsSkin

Thyroid

Predisposition to Type I Diabetes Mellitus

Asp

Uncharged aa

DR3/DR4

How Microbes and their Products can Trigger Autoimmune

Diseases

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

Classification of Autoimmune Diseases Based on Mechanism of

Tissue Damage• Type II: Antibodies

against cell surfaces– Autoimmune hemolytic

anemia– Autoimmune

thrombocytopenic purpura

– Goodpasture (basement membrane in kidney)

– Pemphigus vulgaris– Graves disease (TSH-

Rec.)– Myasthenia gravis

(ACH-Rec.)– Acute rheumatic fever

• Type III: Antibody:Antigen Complexes– SLE (nuclear antigens)– Rheumatoid arthritis

• Type IV: T cell mediated– Diabetes mellitus

(insulin)– Rheumatoid arthritis– Multiple sclerosis

Classification of Autoimmune Diseases by

LocalizationAntigen expressed

only in the affected organ

Abundant ubiquitous antigen

Secondary Effects of Autoimmune Reactions

• Deposit of immune complexes

• Complement activation triggering inflammation

• Removal of complement -covered antigen by erythrocytes

• Sequestration in spleen, liver

Autoimmune Hemolytic Anemia

• Autoantibodies against surface molecule of erythrocytes

• IgG and IgM cotaed eruthrocytes are rapidly cleared– IgG: Phagocytosis– IgM: complement

actvation and then phagocytosis or hemolysis

• Anemia

IgMIgG

Myasthenia Gravis

• Autoantibodies against acetylcholine receptor

• Receptor inactivation and degradataion

• 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

Grave’s Disease

• Autoantibodies against receptor for thyroid stimulating hormone (TSH)

• Activate receptor leading to excessive thyroid hormone production

Systemic Lupus Erythematosus (SLE)

• 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

T-Cell Mediated Autoimmune Disease: Diabetes Mellitus

Type I• Insulin Dependent

Diabetes Mellitus (IDDM)

• Early, sudden onset (adolescence)

• Initially mediated by autoantibodies against -cell antigen

• Later phases include cytotoxic T-cell response

Immunohistochemistry Insulin = brown

Glucagon = black

Normal IDDM

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

Diagnostics of Autoimmune Diseases

• Elevated general inflammation markers– Erythrocyte sedimentation rate– CRP (C-reactive protein)

• Detection of autoantibodies– Immunofluorescence

• Incubate tissue sections with patient serum (indirect assay)

• Detect bound patient antibodies with fluorescent secondary antibodies (direct assay)

– Ouchterlony (Double immunodiffusion)– ELISA– Western blot– Radioimmunoprecipitation

Antinuclear Antibodies: Epitop- Dependent Staining

Patterns

Speckled staining(red is counter stain)

Homogenous staining

Therapeutic Approaches of Autoimmune Diseases

• Plasmapheresis – remove circulating

antibodies– short term

• Immunosuppression– Steroids– Cyclosporin A

• Organ specific– Insulin in DM– Acetylcholine

esterase inhibitor in Myasthenia gravis

Transplantation Immunology

Tissue Commonly Transplanted and Graft

Survival

Graft Rejection

• Graft rejection is an immunological response mediated primarily by T-cells

• Major antigens involved : MHC complex• Minor antigens: Minor H antigens

– Allelically variable non-MHC proteins– Presented via MHC I molecules– Rejection is slower

Graft Rejection is Specific

• Graft APC migrate to host lymph node• Present graft antigen to host T cells• Host T cell activation • Migration of activated anti graft T cells to the grafted tissue

and destruction

• Passenger leukocytes in grafts

• Donor APC, bear allogenic MHC and co-stimulatory factors

• Activate alloreactive recipient T cells

• Recipient APC take up donor antigen

• Recipient T cells are activated by recipient APC

Graft(donor)

Recipient

Alloantigens in Grafted Organs are Recognized in Two Different

Ways

Hyperacute Graft Rejection

• Recipient has preexisting ABO antibodies– Previous blood transfusions– ABO antigens also present on

leukocytes, endothelial cells• During surgery antibodies

bind to endothelial vessels of graft

• Immediate activation of complement, blood clotting

• Can be prevented by cross matching donor and recipient

Graft versus Host Disease

• Major problem in allogenic bone marrow transplantation

• Mature T cells, which contaminate bone marrow, recognize tissue of recipient

• Severe inflammatory disease– Rashes– Diarrhea– Liver disease

Mixed Leukocyte Culture• To detect tissue incompatibilities• Mix leukocytes form potential donor with

irradiated leukocytes from potential recipient and vice versa

• If mismatch donor leukocytes will proliferate and lyse host cells and vice versa

The Fetus is an Allograft that is Typically Not Rejected

• Fetus is detected as mothers generate antibodies against father’s MHC proteins

• Placenta sequesters fetus from maternal T cells

• Trophoblast is major protective layer– Does not express MHC I and II– Expression of non-classical

MHC molecules that bind to inhibitory NK cell receptors

– Active tryptophan depletion– Secretion of inhibitory

cytokines (IL10, TGF, IL4)

Additional Resources

Accessed 5/21/2008http://www.mayoclinicproceedings.com/images/7508/7508cr4-fig1.jpg

http://www.bio.davidson.edu/Courses/Immunology/Students/Spring2003/Super/handsofRA.jpg