Autoimmunity

“n. of, relating to, or caused by autoantibodies or lymphocytes that attack molecules, cells, or tissues of the organism

producing them.”

(from Webster’s Online)

The Study of Autoimmunity

• Molecular Mechanisms of Autoimmunity

• Animal Models for Autoimmune Dysfunction

• Treatments for Autoimmune Diseases

• Gender Differences in Autoimmunity

• Three Common Autoimmune Diseases

Molecular Mechanisms of Autoimmunity

What could go wrong here?

How is autoimmunity induced?

Molecular Mechanisms of Autoimmunity

• Cross-reactivity (Molecular and Viral Mimicry)

Viral and nonviral peptides can mimic self-peptides and induce autoimmunity

Example: papilloma virus (HPV) and insulin receptor

Cross-Reactivity

Molecular Mechanisms of Autoimmunity

• Release of Sequestered Antigen

Antibodies in blood can attack Myelin Basic Protein if Blood-Brain barrier is breached.

Molecular Mechanisms of Autoimmunity

• Inappropriate MHC expression

Type I Diabetes: Pancreatic β cells express abnormally high levels of MHC I and MHC II (?)

MHC II – APC only! This may hypersensitize TH cells to β cell peptides.

Inappropriate MHC Expression

Normal Pancreas Pancreas with Insulitis

Fig. 20-3

Molecular Mechanisms of Autoimmunity

• Polyclonal B Cell Activation by Viruses and Bacteria

If B cells reactive to self-peptides are activated, autoimmunity can occur.

Example: Epstein-Barr Virus, which is the cause of infectious mononucleosis.

Putting it all together…the big picture

• Autoimmunity can be caused by immunological, genetic, viral, drug-induced, and hormonal factors.

• There are 4 immunological mechanisms of autoimmunity.

• All mechanisms cause abnormal B or T cell activation.• Centrality of the Ternary Complex• Most instances of autoimmune diseases occur with

multiple mechanisms, which makes treatment difficult.

Animal Models for Autoimmune Diseases

Why have them?

• Animal models of autoimmune diseases contribute valuable insights into the mechanisms of autoimmunity and to our understanding of autoimmunity in humans and how we may treat autoimmune diseases.

Autoimmunity in Animals is Spontaneous or Induced

• Spontaneous: Autoimmunity develops spontaneously in some inbred strains of animals

• Induced: Autoimmunity develops after being induced by certain experimental manipulation

Spontaneous Autoimmunity in Some Animals

• Exhibits important clinical and pathogenic similarities to certain autoimmune diseases in humans

• Example: New Zealand Black Mice (NZB) and F1 hybrids of NZB and New Zealand White Mice (NZW) spontaneously develop autoimmune diseases that closely resemble lupus erythematosus– Incidence of autoimmunity in hybrids is more common

in females than in males

New Zealand Mice

• NZB spontaneously develops autoimmune hemolytic anemia between 2-4 months of age– At this point various antibodies can be detected.

These antibodies include antibodies to erthyocytes, nuclear proteins, DNA and T lymphocytes

– F1 hybrids develop glomerulonephritis from immune-complex deposits in the kidneys and die within 18 months

• Glomerulonephritis: nephritis marked by inflammation of the capillaries of renal glomeruli

– Glomeruli: a tuft of capillaries at the point of origin of each vertebrate nephron that passes a protein-free filtrate to the surrounding Bowman’s capsule

Mouse MRL/lpr/lpr (Mouse strain)

• Systemic Lupus Erthematosus develops in the mouse strain MRL/lpr/lpr– Mice are homozygous for the lpr gene, which has

been identified as a defective fas gene. – The fas/lpr gene product is a cell surface protein in

the TNF family– When the normal fas protein interacts with its

ligand, signals are sent out leading to apoptic death of the fas bearing cells: target of CTLs

– Fas is also known to be important for the death of hyperactive CD4+ cells

– Without fas mature peripheral T cells do not die, and they continue to proliferate and produce cytokines that result in enlarged lymph nodes and spleen

Nonobese Diabetic (NOD) Mouse Model

• Found to develop a form of diabetes that resemble human insulin dependent mellitus

• As in humans, NOD in mice begins with lymphatic infiltration into the islets of the pancreas

• There is an association between certain MHC and development of diabetes in the mice

• Experiments have shown that t cells from diabetic mice can transfer diabetes to nondiabetic mice

• When bone marrow of a normal mouse is replaced with NOD bone marrow, diabetes develops

• When bone marrow from NOD mouse is replaced with healthy bone marrow, diabetes doesn’t develop

Spontaneous Autoimmunity

• A final example….- Other animals: Obese strain chickens can develop humoral and cellmediated reactivity thyroglobulin resembling Hashimoto’s Thyroiditis

Induced Autoimmunity in Animals

• Autoimmune dysfunctions that are similar to human autoimmune disease can be induced into animals

Myasthenia Gravis

• 1973: rabbits were immunized with acetylcholine receptors purified from electric eels. The rabbits then developed muscular weakness similar to myasthenia gravis

• Myasthenia gravis: disease characterized by progressive weakness and exhaustibility of voluntary muscles without atrophy or sensory disturbance and caused by an autoimmune attack on acetylcholine receptors at the neuromuscular junction

• Experimental myasthenia gravis resulted when the antibodies to the acetylcholine receptors blocked muscle stimulation by the acetylcholine in the synapse

• From this experiment: the discovery that auto-antibodies to the acetylcholine receptors were the cause of myasthenia gravis in humans

CFA: Complete Freund’s AdjuvantAn effective means of potentiating humoral antibody response to injected immunogens

•Improper or unnecessary use leads to excessive inflammation, induration, and/or necrosis in laboratory animals.

•CFA is considered to be an emulsion consisting of equal volumes of CFA to antigen (1 part CFA or less to 1 part antigen).

Experimental Autoimmune Encephalomyelitis (EAE)

• Experimental autoimmune encephalomyelitis (EAE): one of the best studied models of autoimmune diseases

• Encephalomyelitis: concurrent inflammation of the brain and spinal cord

• EAE is mediated by T cells and can be induced in many species by immunization with a myelin basic protein (MBP) or protolipid protein (PLP) in complete Freund’s adjuvant (20-7)Within 2-3 weeks animals develop cellular infiltration of the myelin sheaths of the central nervous system: resulting in demyelination or paralysis.

• Most animals die, but some have milder symptoms. Some develop chronic symptoms that resemble multiple sclerosis in humans.

• Animals that recover are resistant to more MBP injections• EAE model is used to investigate treatment testing for human MS• Recent mouse experiments suggest that orally administered MBP

may make these antigen-specific peripheral T cell clones self-tolerant• Paved the way for clinical trials in MS patients

Experimental AutoimmuneThyroiditis (EAT)

• Induced in a number of animals by immunizing them with thyroglobulin using CFA: humoral and Tdth cell responses cause inflammation of the thyroid.

• EAE resembles human hashimoto’s thyroiditis• Autoimmune Arthritis is induced by immunizing

rats with Mycobacterium tuberculosis in CFA• Animals develop symptoms similar to human

rheumatoid arthritis

Other Autoimmune Animal Models

Treatment of Autoimmune Diseases

I. Current Therapies

- aimed at reducing symptoms by providing non-specific suppression

of the immune system

II. Experimental Therapeutic Approaches - try to induce specific immunity

I. Current Therapies

• Immunosuppressive drugs- corticosteroids, azathioprine- slows the proliferation of lymphocytes

• Cyclosporin A

- blocks signal transduction mediated by the TCR (inhibits only antigen-activated T cells while

sparing non-activated ones)• Thymectomy

- removal of thymus from patients with myasthenia gravis

• Plasmapheresis- removes antigen-antibody complexes for a short- term reduction in symptoms

II. Experimental Therapeutic Approaches

• T-cell Vaccination

- autoimmune T-cell clones elicit regulator T-cells that are specific for the TCR on the autoimmune

T- cells

- results in suppression of the autoimmune cells• Peptide Blockade of MHC molecules

- a synthetic peptide is used to bind in place of the regular peptide on the MHC

- induces a state of clonal anergy in the autoimmune T-cells

(Experimental Therapies continued)

• Monoclonal-Antibody Treatment

- monoclonal antibody against the IL-2 receptor blocks activated TH-cells

- blockage of preferred TCRs with monoclonal antibodies

- monoclonal antibody against an MHC molecule that is associated with autoimmunity while

sparing the others• Oral antigens

- tend to induce tolerance

- still in early clinical trials

Sex-based Differences in Autoimmunity

• Differences can be traced to sex hormones- hormones circulate throughout the body and

alter immune response by influencing gene expression

- (in general) estrogen can trigger autoimmunity and testosterone can protect against it

• Difference in immune response- ♀ produce a higher titer of antibodies and mount more vigorous immune responses than ♂- ♀ have a slightly higher cortisol secretion than ♂- ♀ have higher levels or CD4+ T-cells and serum IgM

Sex-based Differences

• Estrogen

- causes autoimmunity (generally)

- stimulates prolactin secretion (helps regulate immune response)

- stimulates the gene for CRH (corticotropin- releasing hormone) that promotes cortisol

secretion

- causes more TH1-dominated immune responses

(promotes inflammation)• Testosterone

- can cause autoimmunity or protect against it

Sex-based Differences• Pregnancy

- during this, ♀ mount more of a TH2-like response

- the change in hormones creates an anti- inflammatory environment (high cortisol levels)

- diseases enhanced by TH2-like responses are exaggerated and diseases that involve inflammatory responses are suppressed

- fetal cells can persist in the mother’s blood or the mother’s cells may appear in the fetus

(microchimerism)

- can result in autoimmunity if the fetal cells mount an immune response in the

mother’s body (or vice versa)

Rheumatoid Arthritis (RA)

• Cause (s) and Demographics

• Molecular Mechanism

• Mechanism of Tissue Damage

• Treatment Options

Cause and Demographics

• Cause is unknown!

• Affects 1-2% of worldwide population

• Patients are 75% Women, between 40-60 years of age

Molecular Basis

• Rheumatoid Factor (Rf): Antibodies to IgG• HLA-DR4 Antibody (MHC II!)

Mechanism of Tissue Damage

Treatment Options

• NSAIDs

• Cox-2 Inhibitors

• Methotrexate

• Herbal Remedies– Glucosamine– Chondroitin

Grave’s Disease•Production of thyroid hormones is regulated by thyroid-stimulating hormones (TSH)•The binding of TSH to a receptor on thyroid cells activates adenylate cyclase and stimulates the synthesis of two thyroid hormones: thyroxine and triiodothyronine•A person with Grave’s Disease makes auto-antibodies to the receptor for TSH. The binding of these auto-antibodies to the receptor mimics the normal action of TSH, without the regulation, leading to overstimulation of the thyroid•The auto-antibodies are called long-acting thyroid stimulating hormones

Grave’s Disease•Beta-blockers such as propranolol are often used to treat symptoms of rapid heart rate, sweating, and anxiety until the hyperthyroidism is controlled. •Hyperthyroidism is treated with antithyroid medications, radioactive iodine or surgery.•Both radiation and surgery result in the need for lifelong use of replacement thyroid hormones, because these treatments destroy or remove the gland.

Autoimmune Anemias• Pernicious Anemia

What is it?- deficiency in vitamin B12

What causes it?- auto-antibodies to intrinsic factor

What happens? - B12 remains in the stomach and is excreted

Treatment- treated with injections of B12

• Hemolytic Anemia- results from monoclonal antibodies to normal RBC constituents

- antibodies coat the erythrocytes, causing clumping, lysis, and premature clearance by the spleen

- can be induced by an “offending” agent (parasite, drug, or toxin) that adheres to the RBC

- Drug-induced Hemolytic Anemia- drug binds to RBC’s and causes them to become

antigenic

- antibodies that develop from the drug recognize these cells and they are

lysed