Autoimmune Disease and Hypersensitivities Notes

Organs of the Immune System

• Innate Immunity (rapid response)
  • Cells: Macrophage, Natural Killer Cell, Dendritic cell, Neutrophil, Eosinophil, Basophil, Natural Killer T Cell
• Adaptive Immunity (slow response)
  • Cells: B Cell (produces antibodies), T Cell (CD4+, CD8+)
• Organs:
  • Tonsils and Adenoids
  • Lymph Nodes
  • Lymphatic Vessels
  • Thymus
  • Spleen
  • Appendix
  • Peyer's Patches
  • Bone Marrow

Cells of the Immune System

• Derived from myeloid and lymphoid stem cells
• Myeloid Stem Cell Lineage:
  • Myeloblast -> Granulocytes (Eosinophil, Basophil, Neutrophils)
  • Phagocytes (Neutrophils, Macrophages)
• Lymphoid Stem Cell Lineage:
  • Lymphoblasts -> T-cells (Suppressor, Helper, Cytotoxic)
  • B lymphocyte -> Plasma cells (Clonal B-cells that produce Antibodies), Memory B-cells
  • Natural killer cell, T lymphocyte killer cell
• Immune System Types:
  • Innate (Physical barriers: Skin, Mucous membranes, Saliva, Flushing action of urine and tears, Stomach acid)
  • Acquired
    • T-cell immunity (cell-mediated immunity)
    • B-cell immunity (humoral immunity)
• Complement System:
  • Alternative pathway
  • Classical pathway
• Functions:
  • Stops infection before it enters the body
  • Direct killing of bacteria
  • Death of the body's cells infected with a virus or otherwise damaged
  • Death of dangerous organisms

Cytokines

• Cell signaling molecules that aid cell-to-cell communication in immune responses
• Stimulate the movement of cells towards sites of inflammation, infection, and trauma
• Peptide, protein, and glycoprotein forms (proteins with a sugar attached)
• Examples: Interleukin (IL), Interferon (IF), Tumor Necrosis Factor (TNF)
• Produced by macrophages, lymphocytes, mast cells, endothelial cells, and fibroblasts.

Autoimmune Diseases

• Immune system turns on healthy cells
• Impacts anyone, almost 80% are women
• Over 80 different autoimmune diseases
• Hallmark symptoms: fatigue, dizziness, and low-grade fever; classic sign is inflammation
• Pathology:
  • Destruction of body tissue
  • Abnormal growth of an organ
  • Changes in organ function
• Affected areas:
  • Blood vessels
  • Connective tissues
  • Endocrine glands (thyroid or pancreas)
  • Joints
  • Muscles
  • Red blood cells
  • Skin
• Examples:
  • GIT Tract: Crohn's, Ulcerative colitis, Celiac disease
  • Rheumatoid arthritis
  • Systemic lupus erythematosus (SLE)
  • Psoriasis
  • Endocrine: Type I diabetes, Hashimoto's thyroiditis, Graves disease
  • CNS: MS, Parkinson's disease, Autism (speculative)

Specific Autoimmune Diseases

Rheumatoid Arthritis

• Immune system produces antibodies that attach to the linings of joints.
• Immune system cells then attack the joints, causing inflammation, swelling, and pain.
• Untreated: causes permanent joint damage.
• Treatments: oral or injectable medications that reduce immune system over activity.

Systemic Lupus Erythematosus (Lupus)

• Autoimmune antibodies attach to tissues throughout the body.
• Commonly affected: joints, lungs, blood cells, nerves, and kidneys.
• Treatment: daily oral prednisone (steroid that reduces immune system function).

Hashimoto's Thyroiditis

• Antibodies attack the thyroid gland, destroying cells that produce thyroid hormone.
• Leads to low levels of thyroid hormone (hypothyroidism).
• Symptoms: fatigue, constipation, weight gain, depression, dry skin, and sensitivity to cold.
• Treatment: daily oral synthetic thyroid hormone pill.

Inflammatory Bowel Disease (IBD): Crohn’s, Ulcerative Colitis

• Symptoms:
  • Diarrhea
  • Fever
  • Fatigue
  • Abdominal pain and cramping
  • Blood in stool
  • Mouth sores
  • Reduced appetite and weight loss
  • Pain or drainage near or around the anus (fistula)
• Severe Crohn's disease may also experience:
  • Inflammation of skin, eyes, and joints
  • Inflammation of the liver or bile ducts
  • Delayed growth or sexual development in children

Compare Crohn's Disease and Ulcerative Colitis

• Crohn's Disease
  • Location: Entire gastrointestinal tract, most commonly transition between the small and large intestine
  • Disease development: Uneven spread, inflamed segments between healthy areas
  • Potential intestinal symptoms: Abdominal pain, Weight loss, Diarrhea
  • Potential extraintestinal symptoms: Fistulas, abscesses, anemia, fever, arthritis and skin changes
• Ulcerative Colitis
  • Location: Colon mainly, although gastritis is recognized
  • Disease development: Uniform progression spread from the rectum through the colon
  • Potential intestinal symptoms: Bloody diarrhea, Abdominal pain, Weight loss, Ulceration and bleeding
  • Potential extraintestinal symptoms: Liver diseases, anemia, fever, arthritis and skin changes

Celiac Disease

• Immune system attacks gluten proteins (wheat, barley, or rye).
• Destroys villi in the small intestine, leading to nutritional deficiencies.
• Complications:
  • Malnutrition/Malabsorption
  • Growth delay
  • Osteoporosis (Calcium & Vitamin D deficiency)
  • Lactose Intolerance
  • Abdominal pain/Diarrhea
  • Cancer (Intestinal lymphoma/Bowel cancer)
  • Neurological (Seizures/Peripheral neuropathy)

Multiple Sclerosis (MS)

• Neurodegenerative disorder affecting the central nervous system (CNS).
• Loss of myelin sheaths surrounding the axons of neurons, leading to inflammatory demyelination.
• Specific CD4 T cells attack the myelin sheaths
• Main Symptoms:
  • Central:
    • Fatigue
    • Cognitive impairment
    • Depression
    • Anxiety
    • Unstable mood
  • Visual:
    • Nystagmus
    • Optic neuritis
    • Diplopia
  • Speech:
    • Dysarthria
  • Throat:
    • Dysphagia
  • Musculoskeletal:
    • Weakness
    • Spasms
    • Ataxia
  • Sensation:
    • Pain
    • Hypoesthesias
    • Paraesthesias
  • Bowel:
    • Incontinence
    • Diarrhea or constipation
  • Urinary:
    • Incontinence
    • Frequency or retention

Autism

• Neurodevelopmental disorder, identified early in childhood (typically three years of age).
• Impaired communication and social interaction, and behavioral issues
• Autism spectrum disorders (ASD) are a collection of developmental neurobehavioral conditions
  • Autistic disorder
  • Asperger’s disorder
  • Pervasive developmental disorder
• Predominantly a heritable disorder (80-90%)
• Epidemiologic studies suggest environmental factors may play a role, such as toxic exposures, teratogens, perinatal insults, prenatal infections (rubella and cytomegalovirus)
• Link between autoimmune dysfunction and neurodevelopmental diseases is hypothesized based on immunological abnormalities found in autistic patients, but remains unproven.
• Areas of the Brain Effected
  • Frontal lobe
  • Hypothalamus
  • Thalamus
  • Amygdala
  • Hippocampus
  • Cerebellum
  • Spinal chord
• Affect on Brian Cells
  • Cells are smaller, more densely packed in certain areas
  • Have shorter, less developed branches

Causes of Autoimmune Disease: Leaky Gut

• Triggers: Gluten, Toxins, Stress, Infections, Drugs, Pathogens, Food Particles
• Progression of Leaky Gut:
  • Gl inflammation -> Infection
  • Intestinal mucosal cells change permeability
  • Intestinal Immune Complex enters Blood Stream -> Systemic Inflammation -> Poor Health

Gut Permeability

• Healthy Digestive Tract:
  • Closed and closely packed mucosal cells lining the digestive tract
  • Cells are plumped up, thereby carefully controlling the absorption of nutrients from food
  • Normal tight junction between cells keeps the mucosal barrier intact.
  • This barrier prevents most large molecules and germs passing from inside the bowel into the bloodstream.
• Unhealthy Permeable Gut Lining (Leaky Gut):
  • Excess inflammation damaging cells and epithelium
  • Undigested food particles may pass through gaps
  • The immune system may react to this by creating more Inflammation
  • Commonly leads to food intolerances - an immune reaction to various foods which can change over time
  • A leaky gut is often an ongoing issue and frequently undiagnosed

Diagnosis of Leaky Gut

• Tests:
  • IGg Food Intolerance Test
  • Stool Tests
  • Organic Acid
  • Vitamin and Mineral Deficiencies Tests
  • Zonulin or Lactulose Tests
• Zonulin:
  • Controls the size of the openings between gut lining and the bloodstream
  • enzyme-linked immunosorbent assay test (ELISA) serum levels of zonulin: biomarker of how much intestinal permeability
• Dysbiosis
  • Trillions of microorganisms – fungal, bacterial and viral
  • Commensal and beneficial organisms
  • Functions in tandem - host’s defenses and the immune system
  • Protect against pathogen colonization and invasion.
  • Metabolic function - source of essential nutrients and vitamins
  • Extraction of energy and nutrients, such as short-chain fatty acids (SCFA) and amino acids, from food.
• Imbalance gut microbiome (Bacteria, Yeast, Parasites, Foodborne pathogens) can trigger both local and systemic inflammation
• Altering the composition of the microbiota and barrier function
• Misuse and overuse of Antibiotics!

Multiple Autoimmune Syndrome (MAS)

• Poly-autoimmunity - presence of more than one autoimmune disease in a single patient.
• Defined as occurrence of at least three autoimmune diseases in a same patient
  • type 1 MAS
  • type 2 MAS
  • type 3 MAS
• Celiac disease isn’t included in MAS

Sex Differences in Immunological Responses

• Differences in innate and adaptive immune responses.
• Certain immunological differences are present throughout life whereas others are only apparent after puberty and before reproductive senescence suggesting that both genes and hormones are involved.
• Environmental exposures influence the microbiome and contribute to variations in the incidence of autoimmune diseases and malignancies, susceptibility to infectious diseases and responses to vaccines in males and females.

Inflammation Markers

• Acute phase response: chronic conditions, including malignancy and infection.
• Acute-phase reactants: increase or decrease by 25% or more during inflammation.
  • C-reactive protein (CRP)
  • Erythrocyte sedimentation rate (ESR)
• Nonspecific
• Simple and cost-effective diagnostic tool to monitor the response to treatment for a number of disorders.

C-Reactive Protein (CRP)

• Produced in the liver – hepatocytes
• Measured in milligrams of CRP per liter of blood (mg/L)
• Median concentration of CRP is 0.8 mg/l – half-life 19 hours
• Levels:
  • 1 mg/L - low risk of cardiovascular disease
  • 1 and 3 mg/L - intermediate risk
  • 3 mg/L - risk for cardiovascular disease.
  • >10 mg/L significant inflammation e.g. autoimmune, cancer, TB

Erythrocyte Sedimentation Rate (ESR)

• Rate of sedimentation of erythrocytes (red blood cells) in a sample of blood that has been placed into a tall, thin, vertical tube
• Results are reported as the millimeters of clear fluid (plasma) present at the top portion of the tube after one hour.
• ESR typically begins to increase within 24 hours after insult.
• Half-life of fibrinogen is about 100 hours and that of IgG is more than a week, ESR can remain elevated for weeks after the initial rise
• Marked ESR increases (>100 mm/hr) are associated with infection (33%), neoplasm (17%) end stage renal disease (17%)
• Age, sex, and anemia are other non-inflammatory causes of increased ESR.
• There are additionally many reasons a patient might have a misleadingly low ESR. Abnormal erythrocytes and high serum bile salts

Treatment of Autoimmune Diseases

• Traditional therapies: immunosuppressive medications and NASIDs (small molecules)
• Highly effective but long-term treatments with high doses can lead to:
  • Susceptibility to life-threatening opportunistic infections
  • Long-term risk of malignancy
  • Toxicity and serious side effect profiles
• Optimal Therapy Goals:
  • Specifically targets the pathogenic cells and leaves the remainder of the immune system functioning normally
  • Reestablishes immune tolerance that is stable over time, such that continuous or long-term therapy is not needed
  • Has low toxicity and few side effects
  • Is overall cost-effective when compared to alternative approaches

Immunosuppressant Classes

Non-Selective

• Corticosteroids
  • Prednisone (PO) & Methylprednisolone (IV)
• Antimetabolite (DNA synthesis inhibitors)
  • Azathioprine & Myclophenolate mofetil
• Immunoglobulins
• Anti-lymphocyte antibodies

Selective

• Calcineurin Inhibitors
  • Cyclosporine
  • Tacrolimus (Rapamycin)
• Selective IL-2 Receptor antagonists
  • Basiliximab, Daclizumab & Infliximab
• Mamalian target of Rapamycin (mTOR) inhibitors
  • Sirolimus

Mechanism of Action of Immunosuppressive Agents

• Steroids: Inhibition of gene transcription for secretion of inflammatory cytokines. Reduces leukocyte migration, phagocytic function of neutrophils and monocytes, and T-cell function.
• Azathioprine, 6-Mercaptopurine: Purine antimetabolite. Apoptosis of T lymphocytes
• Methotrexate: Folic acid antagonist; inhibition of purine synthesis. Actual cell targets involved in suppression of inflammation: unknown
• Cyclosporine, tacrolimus: Inhibition of cytosolic enzyme calcineurin. Suppression of cell-mediated immunity
• Anti-TNF agents: Selective inhibition of cytokines. Inhibition of inflammatory cells; reduction of inflammatory proteins.

Monoclonal Antibodies (mAbs)

• Revolutionized the treatment of autoimmune diseases
• Autoimmune diseases characterized by the activation of autoreactive CD4+ lymphocytes in the peripheral lymph nodes
• Activated T cells proliferate and migrate into the disease-targeted organ parenchyma
• Mechanisms of mAbs to treat autoimmune disorders:
  • Blockade and depletion of T cells and/or B cells
  • Inhibition of the interaction between T cells and antigen-presenting cells
  • Blockade of T- and B-cell recruitment
  • Blockade of T-cell differentiation or activation
  • Blockade of pro-inflammatory cytokines (most widely used approach, especially TNF-α)

Therapeutic mAbs Used for Inhibition of Autoimmune Reactivity

• Adalimumab
  • Type:
    • Human, IgG1
  • Target:
    • TNF-α
  • Medical uses:
    • Rheumatoid arthritis, Crohn's disease, plaque psoriasis, psoriatic arthritis, ankylosing spondylitis, juvenile idiopathic arthritis.
• Alemtuzumab
  • Type:
    • Humanized, IgG1
  • Target:
    • CD52
  • Medical uses:
    • Multiple sclerosis
• Belimumab
  • Type:
    • Human, IgG1
  • Target:
    • BAFF
  • Medical uses:
    • Systemic lupus erythematosus
• Benralizumab
  • Type:
    • Humanized, IgG1
  • Target:
    • CD125
  • Medical uses:
    • Asthma
• Brodalumab
  • Type:
    • Human, IgG2
  • Target:
    • IL-17
  • Medical uses:
    • Plaque psoriasis
• Canakinumab
  • Type:
    • Human, IgG1
  • Target:
    • IL-1
  • Medical uses:
    • Cryopyrin-associated periodic syndrome
• Certolizumab pegol
  • Type:
    • Humanized, Fab', IgG1
  • Target:
    • TNF-α
  • Medical uses:
    • Crohn's disease, rheumatoid arthritis, axial spondyloarthritis, psoriatic arthritis
• Golimumab
  • Type:
    • Human, IgG1
  • Target:
    • TNF-α
  • Medical uses:
    • Rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis
• Guselkumab
  • Type:
    • Human, IgG1
  • Target:
    • IL23
  • Medical uses:
    • Psoriasis
• Infliximab
  • Type:
    • Chimeric, IgG1
  • Target:
    • TNF-α
  • Medical uses:
    • Rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis, psoriasis, Crohn's disease, ulcerative colitis
• Itolizumab
  • Type:
    • Humanized, IgG1
  • Target:
    • CD6
  • Medical uses:
    • Psoriasis
• Ixekizumab
  • Type:
    • Humanized, IgG4
  • Target:
    • IL-17A
  • Medical uses:
    • Plaque psoriasis

Comparison of Small Molecules and Monoclonal Antibodies

Pharmacodynamics of mAbs

• High affinity and selectivity of mAbs make them less likely to have off-target effects
• Can identify the role of a target in disease pathology
• MAbs may have intrinsic activity as full/partial agonists or allosterically modulate a receptor.
• Technology now available to generate very high affinity variants
• MAbs can be engineered to have dual targeting efficacy
• obinutuzumab (Gazyva), an anti-CD20 mAb with enhanced FcγR binding affinity and increased potency

Antibody-Drug Conjugates (ADCs)

• mAbs conjugated with highly cytotoxic small molecules (payloads) through chemical linkers
• Used for targeted cancer therapy
• trastuzumab-emtamsine (Kadcyla ®), targets the HER2 receptor

Pharmacokinetics - ADME

• MAbs do not have good oral bioavailability (<<1%)
• Administered mostly by intravenous (IV), subcutaneous (SC), and intramuscular (IM) injections.
• Absorption process for IM or SC injected mAbs:
  • Through the interstitial space and into the lymphatic system, with subsequent draining into the systemic circulation
  • Peak plasma concentration achieved 3‐7 days after administration
• Have a very long half‐life in circulation, typically 11‐30 days in humans
• IgG Fc region has a recognition domain for the neonatal Fc Receptor (FcRn), which is constitutively expressed in the vascular endothelium and recycles IgG
• MAbs extravasate into the tissues and distribute in the interstitial space
• Extravasation occurs mainly through convective transport and transcytosis through vascular epithelial cells.
• MAbs have low volumes of distribution at steady state (3‐8 L)
• Most small molecule drugs are metabolized through cytochrome P450 (CYP) and transferase enzymes in the liver and excreted through the bile or the kidney.
• MAbs are not metabolized by CYP enzymes thus limiting their toxicity and drug‐drug interactions
• Main form of elimination for mAbs is cellular uptake by pinocytosis into the endosome, followed by intracellular metabolism through lysosomal degradation into peptides and amino acids
• Can lead to immunodeficiency, leaving patients more susceptible to infectious diseases.

New therapeutic strategies for autoimmune disorders

• Antibody therapy, RNA interference (RNAi) therapy, Hematopoietic stem cell transplantation (HSCT) therapy for autoimmune diseases

Antibody Therapy

• Combination of targeted antibody therapies
• Combined treatment may target two or more signaling pathways and achieve synergistic treatment effects.
• therapeutic monoclonal antibodies combined with some chemotherapeutics or other immunosuppressive biologics seem to be more widely applied.
  • study about Certolizumab pegol and methotrexate (MTX) combination treatment showed a significant therapeutic effect without extra side effects compared with placebo + MTX

Bispecific Antibodies Therapies

• Bispecific antibodies (BsAbs) are a new class of antibodies that can identify two different antigens or two different epitopes of the same antigen
• have been applied to the treatment of complex tumors and autoimmune diseases.
• Bimekizumab which can selectively inhibit IL-17A and IL-17F simultaneously is the first BsAbs approved by the FDA in 2021
• Bimekizumab showed non-inferior therapeutic ability to adalimumab in reducing symptoms and signs of plaque psoriasis but had adverse events including higher frequency of oral candidiasis and diarrhea.

RNA Interference Therapy

• RNAi was first discovered in Caenorhabditis Elegans by Fire and Mello in 1998
• Pharmaceutical companies have been devoted to developing the siRNA therapeutics and major breakthroughs were being made that paved the way to successful clinical translation
• In 2018, the FDA approved the first liposome complex for siRNA binding (Patisiran) for the treatment of a rare disease called hereditary transthyretinmediated amyloidosis (hATTR)
• Herman et al. delivered siRNA based on the LNP system to two types of mouse models of RA for hnRNP A2/B1 silence and downregulate the expression of proinflammatory cytokines in macrophages

Hematopoietic Stem Cell Transplantation (HSCT)

• HSCT provides a treatment option to restore immune tolerance by replacing or resetting immune responses
• During the immune reconstitution process, NK cells and B cells recovering faster than T cells, with CD4+ T cells recovered slowly compared to CD8+ T cells based on a study in MS patients after HSCT transplantation.
• The preexisting T cells with pathological and autoimmune reactions will be replaced by newly formed T cells
• After autologous HSCT transplantation in MS patients, B cells shifted from a predominantly transitional to naïve phenotype, and memory B cells recovered slowly with reduced repertoire diversity.
• Tregs play an important role in balancing the body’s immune axis
• TolDCs have enormous potential for the treatment of autoimmune diseases due to their ability to induce immune tolerance
• These tolDCs express low costimulatory molecules and high levels of immunosuppressive membrane surface molecules including programmed cell death ligand (PD-L1) and inhibitory Ig-like transcripts (ILTs), which leads to the T cell clonal anergy and expansion of regulatory T cells eventually.

Hypersensitivity

• Overreaction of the immune system
• Immune system responds disproportionately to stimuli
• Hypersensitivity is a heightened or exaggerated response of the immune system to substances that are generally harmless
• These substances, known as antigens or allergens, trigger an immune response
• Immune system mistakes harmless substances for threats.
• Launches an excessive and damaging response

Hypersensitivity Types and Their Mechanisms

Hypersensitivity Types Explained

Type I: Immediate hypersensitivity (allergic) reactions

• Immediate response upon exposure to an allergen.
• Involves the release of histamine and other inflammatory mediators
• Symptoms: itching, hives, swelling, and anaphylaxis.

Type II: Cytotoxic hypersensitivity

• Activation of the immune system against cells or tissues of the body
• Results in the destruction of healthy cells, often mediated by antibodies targeting specific cell surfaces
• Examples: autoimmune hemolytic anemia and certain drug-induced reactions.

Type III: Immune complex-mediated hypersensitivity

• Formation of immune complexes that deposit in various tissues, leading to inflammation and tissue damage.
• Conditions like SLE and rheumatoid arthritis

Type IV: Delayed hypersensitivity (cell-mediated) reactions

• Delayed immune response mediated by T cells rather than antibodies
• Associated with contact dermatitis

Causes and Triggers of Hypersensitivity

Allergens

• Substances that trigger allergic reactions in hypersensitive individuals.
• Common allergens: pollen, dust mites, pet dander, certain foods, insect venom, and medications

Autoantigens

• Immune system targets the body’s own tissues and cells
• Leads to chronic inflammation and tissue damage: rheumatoid arthritis and SLE

Drugs and medications

• Induce hypersensitivity reactions
• Penicillin and NSAIDs

Infections

• Triggered by infections
• post-streptococcal glomerulonephritis

Clinical Manifestations of Hypersensitivity

Respiratory Symptoms

• sneezing, nasal congestion, coughing, wheezing, and shortness of breath.
• Allergic rhinitis and asthma

Dermatological Symptoms

• itching, redness, hives, eczema, and blistering
• Contact dermatitis and urticaria (hives)

Gastrointestinal Symptoms

• nausea, vomiting, abdominal pain, diarrhea, and anaphylaxis
• Food allergies and certain drug reactions

Systemic Symptoms

• Affecting multiple organ systems.
• Anaphylaxis

Managing Hypersensitivity

Avoidance of Triggers

• Lifestyle modifications, environmental changes, and dietary adjustments

Medications

• Antihistamines, corticosteroids, and bronchodilators

Immunotherapy

• Gradually exposing the individual to increasing amounts of allergens

Epinephrine Auto Injectors

• For individuals at risk of anaphylaxis