Hypersensivity Part I & Part II Up PDF

Clinical Immunology & Serology CLS 311 Mr. Abdullah Abdali CLS Lecturer MSc in Immunology and Immunotherapy Outline Hypersensitivity Classification of Hypersensitivity Pathogenesis Symptoms and Disease. Lab Diagnosis Hypersensitivity Are exaggerated o...

Clinical Immunology & Serology CLS 311 Mr. Abdullah Abdali CLS Lecturer MSc in Immunology and Immunotherapy Outline Hypersensitivity Classification of Hypersensitivity Pathogenesis Symptoms and Disease. Lab Diagnosis Hypersensitivity Are exaggerated or inappropriate immunologic responses occurring in response to an antigen or allergen known as hypersensitivity reactions. Allergen: Any antigen that are harmless in most people, but sometimes causes allergic reactions such as pollens, mites, foods, etc. Antigen: foreign substance (hetero-antigens) that able to induce immune response such as bacteria, viruses, etc, and they are usually proteins compounds. An immune response to an antigen may result in sensitivity to challenge with that antigen, and therefore hypersensitivity is a reflection of excessive or aberrant immune responses. Hypersensitivity Hypersensitivity reactions may occur in three situations. ▪ Responses to foreign antigens (microbes and noninfectious environmental antigens) may cause tissue injury, especially if the reactions are repetitious or poorly controlled. ▪ Responses to allergen antigens ▪ The immune responses may be directed against self (autologous) antigens, as a result of the failure of self-tolerance (autoimmunity) Classification of Hypersensitivity Hypersensitivity reactions are classified on the basis of the principal immunologic mechanism that is responsible for tissue injury and disease. - Antibody mediated hypersensitivity: ❖ Type I (IgE-mediated) ❖ Type II (Fc and complement-mediated – by antibodies that activate cellular cytotoxicity) ❖ Type III (Immune complex-mediated) - Cell mediated hypersensitivity: ❖ Type IV (Delayed-type hypersensitivity – T cell mediated)  Immediate hypersensitivity, or type I hypersensitivity Is a type of pathologic reaction that is caused by the release of mediators from mast cells. Most often depends on the pre-production of immunoglobulin E (IgE) antibody against environmental antigens and the binding of IgE to mast cells in various tissues. Triggered by antigens known as atopic antigens or allergens. Atopy: refers to an inherited tendency to respond to naturally occurring inhaled and ingested allergens with continued production of IgE, the disease known as atopic disease/allergic disease. Examples include asthma, anaphylaxis, allergic rhino conjunctivitis. Most allergic reaction are IgE mediated, therefore, most allergy are Type I hypersensitivity reaction. Develop within minutes of exposure (immediate) Allergens Inhaled or ingested: - Foods - Mold - Drugs/medication - Dander (dead skin) - Bee stings - Pollen - Dust - Mineral - Cow’s milk - Peanuts - Eggs Contact with skin: - latex - Lotions - Soaps Pathogenesis of Type I Hypersensitivity Immediate hypersensitivity reactions are mediated by IgE. T and B cells play important roles in the development of these antibodies. CD4+ T cells classes Cytokines Role/action Th1 IFN-γ and IL-2 Promote cell mediated immune response Th2 IL-4 and IL-13 Act on B cells to promote the production of antigen-specific IgE Th17 IL-17, IL-21, and IL-22 Help fight extracellular pathogens, to produce antimicrobial peptides and promote neutrophils inflammation essential for immunity at the akin and mucosal surfaces. T reg (regulatory) IL-10 and TGF-β Essential in peripheral tolerance and serve to suppress dysregulated (CD4+CD25+FOXP3+) immune responses. Inhibits TH2 cytokine production Memory T cells Rapidly differentiate into effector T cells in secondary immune responses.  Pathogenesis of Type I Hypersensitivity Happens in two steps first exposure “sensitization” and subsequent exposure (gets more serious) People that react to allergens, they usually have a genetic predisposition. The allergen is typically introduced through the respiratory tract (inhaled), through the gastrointestinal tract (ingested) or through contact of the integument (on the skin) The allergen/antigen is then processed by an antigen-presenting cell (APC), such as a dendritic cell, macrophage, or B-cell. The antigen-presenting cell(s) then migrate to lymph nodes, where they prime naïve T- helper cells that bear receptors for the specific antigen. Pathogenesis of Type I Hypersensitivity After antigen priming, naïve T-helper cells differentiate into TH1, TH2, or TH17 cells based upon antigen and cytokine signaling. In the case of allergen sensitization, the differentiation of naïve T-helper cells is skewed toward a TH2 phenotype. These allergen-primed TH2 cells then release IL-4, IL-5, IL-9, and IL-13. IL-5 plays a role in eosinophil development, recruitment, and activation. IL-9 plays a regulatory role in mast cell activation. IL-4 and IL-13 act on B cells to promote production of antigen-specific IgE antibodies. IgE antibodies then sensitize mast cells by binding to Fcε Receptor on them and the sensitizatization phase is completed. Pathogenesis of Type I Hypersensitivity Secondary exposure: Sensitized mast cells binds to the antigen (two or more to cross link IgE antibodies) This make mast cell to degranulate and release a group of pro-inflammatory molecules called mediators. These mediators (ex. histamine) are the main responsible of the effect seen in an allergic reaction. Histamine binds the H1 receptors and causes the smooth muscles around the BRONCHI to contract causing: – Airway to get smaller (difficulty breathing) – Blood vessel dilation and increased permeability of the blood vessel walls. Causing Edema (swelling) and Urticaria (hives). Pathogenesis of Type I Hypersensitivity In addition to histamine, mast cells release other prof-inflammatory mediators including: – Pro-inflammatory mediators that activates eosinophils – Proteases that chop up large proteins into small peptides. The effects of these molecules is known as early phase reactions and happen within minutes of the second exposure.  Late Phase Reaction Cytokines produced by mast cells stimulate the recruitment of leukocytes, which cause the late-phase reaction (8-12 hours of second exposure). The principal leukocytes involved in this reaction are eosinophils, neutrophils, Th2 cells, and basophils. These are recruited to the site of inflammation. Mast cell–derived tumor necrosis factor (TNF) and IL-4 promote neutrophil- and eosinophil-rich inflammation. Pro-inflammatory mediators that are involved in late phase are similar to the early phase, except that it include leukotrienes (made of fatty acid and facilitate communication between local group of cells). Particularly, LTB4 and LTC4 can cause smooth muscles contraction (like histamine) as well as attracting immune cells such as neutrophils , mast cells, and eosinophils to the site of infection even after the allergen is gone. Different Mediators of Mast Cells Summary  Symptoms of Type I Hypersensitivity reaction Most of patients with type I hypersensitivity can experience mild syndromes or localized allergic reaction including : ▪ Skin (Hives “Urticaria”, and Eczema) ▪ Eyes (conjunctivitis) ▪ Allergic rhinitis (inflammation of the nose) ▪ Bronchopulmonary tissues (Asthma) ▪ Gastrointestinal tract (gastroenteritis) Certain people might experience severe form of allergic reaction (systemic response), especially when they are exposed to a large load of the allergens resulting in that the body cannot supply the vital organs like the brain with enough oxygen. This is known as Anaphylactic shock (Anaphylaxix) Symptoms of Immediate Hypersensitivity Lab Diagnosis Skin test: Cutaneous test (prick test) a small drop of material is injected into the skin at a single point. After 20 minutes, the spot is examined, and the reaction is recorded. Intradermal test (ex Tuberculin test) Uses a greater amount of antigen Only performed if prick test is negative  Lab Diagnosis Radioimmunosorbent test (RIST) – The first test developed for the measurement of total IgE was the competitive radioimmunosorbent test (RIST). – Competitive RIST uses radio- labeled IgE to compete with patient IgE for binding sites on a solid phase coated with anti-IgE. – In noncompetitive RIST solid-phase immunoassay, antihuman IgE is bound to a solid phase such as a paper disk or microtiter well. Patient serum is added and allowed to react, and then a radiolabeled anti—IgE is added to detect the bound patient IgE. Lab Diagnosis Radioimmunosorbent test (RIST) Lab Diagnosis The radioallergosorbent test (RAST- Antigen-Specific IgE Testing): ▪ Is the method of choice for serologic determination of antigen-specific IgE ▪ Useful in the detection of allergies to common allergens such as ragweed, trees, grasses, molds, animal dander, milk, and egg albumin. ▪ Is a noncompetitive solid-phase immunoassay in which the solid phase is coated with specific allergen and reacted with patient serum. ▪ Radioactivity or enzyme activity in the sample is measured. Lab Diagnosis RAST- Antigen-Specific IgE Testing:  Type II Hypersensitivity (Cytotoxic Hyperconnectivity) Refers to an antibody-mediated immune reaction in which antibodies (IgG or IgM) are directed against cellular or extracellular matrix antigens, resulting in cellular destruction, functional loss, or damage to tissues. It is also known as cytotoxic reaction. IgM and IgG antibodies (Ab) that bind to: Intrinsic antigens on cell surfaces (e.g., RBCs) or extracellular materials (e.g., basement membrane) Extrinsic antigens (e.g., blood products, drugs) The killing of cells can occur by one of the three mechanisms: ❖ Complement mediated cell lysis ❖ Antibody dependent cell mediated cytotoxicity (ADCC) ❖ Antibody-mediated cellular dysfunction (non-cytotoxic):  Pathogenesis of Type II Hypersensitivity The first mechanism of cytotoxic type II hypersensitivity is: ❖ Activation of complement system is a family of small proteins that work in enzymatic cascade to fight against bacterial infections using variety of mechanisms. This mechanism include: A. C3a, C4a, and C5a: ▪ Mediators of inflammation = anaphylatoxins ▪ Mast cell and basophil degranulation ▪ C5a also causes neutrophil chemotaxis ▪ This might result in autoimmune Haemolytic anemia, Thrombocytopenia, and Neutropenia Pathogenesis of Type II Hypersensitivity B. C5b and C6, C7, C8, C9: ▪ Membrane attack complex (MAC) Attaches to cell membrane and creates ion- permeable channels causing osmotic changes and cell lysis Pathogenesis of Type II Hypersensitivity C. C3b (opsonisation): ▪ An opsonin (tags antigens for elimination by phagocytes = opsonization) mediating phagocytosis of target cells Examples: transfusion reaction, autoimmune hemolytic anemia  Pathogenesis of Type II Hypersensitivity The second mechanism of cytotoxic type II hypersensitivity is: ❖ Antibody-dependent cell-mediated cytotoxicity (ADCC): ▪ Antibodies , or opsonins, bind their antigen-binding fragment (Fab ) sites to antigens and tag them for phagocytosis. ▪ If antigen-Ab complexes are too large to be phagocytosed, Fc-receptor– bearing effector cells , mainly natural killer (NK) cells, are recruited. ▪ NK cells bind to Fc receptor of Ab → release toxic granules into cells → perforin and granzymes boreholes in membrane → cell lysis Examples: transplant rejection, immune reaction against neoplasm Pathogenesis of Type II Hypersensitivity  Pathogenesis of Type II Hypersensitivity The third mechanism of cytotoxic type II hypersensitivity is: ❖ Antibody-mediated cellular dysfunction (non-cytotoxic): ▪ cell function impaired without cell injury or inflammation ▪ Autoantibodies bind to cell-surface receptors to produce an abnormal activation/blockade of the signaling process. Examples: Myasthenia gravis (Ab causes blockade of acetylcholine receptor) Graves’ disease (Ab causes stimulation of thyroid stimulating hormone (TSH) receptor) Pernicious anemia (Ab against intrinsic factor): Ab prevents absorption of vitamin B12, causing B12 deficiency anemia  Symptoms of Type II Hypersensitivity Human antibody-mediated diseases (type II hypersensitivity): Transfusion reactions (ABO or blood group incompatibility) Goodpasture syndrome: Antibodies attack antigens in the basement membrane of alveoli (pulmonary hemorrhage) and kidneys (nephritis).  Lab Diagnosis Direct antiglobulin test (DAT) is performed to detect transfusion reactions, hemolytic disease of the newborn, and autoimmune hemolytic anemia. The indirect Coombs’ test is used in the crossmatching of blood to prevent a transfusion reaction. ▪ It is used either to determine the presence of a particular antibody in a patient or to type patient red blood cells for specific blood group antigens. Pernicious anemia: CBC, B12, folate level with confirmatory tests if with borderline levels Lab Diagnosis Goodpasture syndrome: Diagnosis: clinical along with labs (antineutrophil cytoplasmic antibodies (ANCA), anti-glomerular basement membrane (anti-GBM) Ab), renal biopsy Acute rheumatic fever: (C-reactive protein (CRP), erythrocyte sedimentation rate (ESR ), antistreptolysin O (ASO)) with Jones criteria echocardiogram Hypersensitivity Part II Immune complex- mediated(Type III Hypersensitivity) Antibodies against soluble antigens may form complexes with the antigens, and the immune complexes may deposit in blood vessels in various tissues, causing inflammation and tissue injury. Such diseases are called immune complex diseases and represent type III hypersensitivity. As with type II hypersensitivity, cell injury is similar: Complement system leads to a reaction that produces cellular damage. Also, IgG and IgM are involved. Develop 4 to 10 days after exposure to antigen and, if exposure to the antigen continues, can become chronic. Immune complex- mediated(Type III Hypersensitivity) Unlike type II hypersensitivity, in type III reactions: ▪ Antigens are not bound to cell surfaces. ▪ Ag-Ab complexes form in circulation ▪ Target of the immune response is not the tissue or cell. ▪ Target is the IC deposited in the tissue. Physiology Immune complex formation normally results in antigen neutralization (blocking the antigen from entering the target cells). The complement system reduces pathologic IC accumulation: Antibodies (Ab) have 2 regions: ▪ Fab region: attaches to antigens ▪ Fc region: interacts with complement and Fc-bearing receptor (FcR) cells (ex. Neutrophils) C1q: activates complement system and binds Ab Fc region, mediating IC clearance by FcR-bearing cells. C3b: makes ICs soluble and tags them for phagocytosis (opsonization). Pathogenesis of Type III hypersensitivity The process takes place in three steps: ❖ Immune complex formation: ▪ Endogenous or exogenous antigen exposure triggers an antibody formation. ▪ In both cases, the antigens bind to antibodies, forming circulating immune complexes, later migrating out of plasma and depositing in host tissues.  Pathogenesis of Type III Hypersensitivity ❖ Immune Complex Deposition: ▪ Physical properties of the IC: o Affinity of Ab to complement, size, and charge of the IC o Increased rate of IC formation → overwhelms clearing mechanism → IC freely circulate out to organs ▪ Antigen-to-antibody ratio: o Low antibodies or excess antibodies → decreased effector activation (insoluble, do not circulate, and are phagocytosed by macrophages in the lymph nodes and spleen) ▪ Tissue specific hemodynamics: o ICs first localize within blood vessels → vasculitis o Common areas affected are “permeability”-susceptible tissues: o Glomeruli (nephritis) o Joints/synovium (arthritis)  Pathogenesis of Type III Hypersensitivity ❖ Inflammatory reaction: IC deposits activate the complement cascade (classical pathway) C3a initiates mast cell degranulation: Histamine increases vascular permeability in the involved tissue. ICs enter tissue → normal tissue with IC becomes a target for inflammatory response. C5a (chemoattractant) recruits neutrophils → release lysozymes and inflammatory mediators → cell death and tissue injury C3b opsonizes the tissue → phagocytosis and membrane attack complex (MAC)- mediated cell lysis Pathogenesis of Type III Hypersensitivity Macrophages and natural killer cells → release lytic mediators and injure tissue cells Platelet aggregation can occur → micro thrombus formation  Disease of Type III Hypersensitivity Arthus reaction: ▪ A locally injected antigen (e.g., immunization like Tdap) causes a localized reaction. ▪ Due to antigen excess and IC deposition on vascular walls ▪ Necrosis of affected tissues: pain, redness , induration, and edema at the site of injection. ▪ Complement is fixed, attracting neutrophils and causing aggregation of platelets. Neutrophils release toxic products such as oxygen- containing free radicals and proteolytic enzymes. ▪ Activation of complement is essential for the Arthus reaction because the C3a and C5a generated activate mast cells to release permeability factors, with the consequent localization of immune complexes along the endothelial cell basement membrane. The Arthus phenomenon. (A) Antigen is injected into the skin of an individual who has circulating antibody of that specificity. (B) Immune complexes are formed and deposit on the walls of blood vessels, activating complement. (C) Complement fragments cause dilation and increased permeability of blood vessels, edema, and accumulation of neutrophils. Disease of Type III Hypersensitivity Serum sickness: ▪ results from passive immunization with animal serum, usually horse or bovine serum, used to treat such infections as diphtheria, tetanus, and gangrene. (systemic administration of a protein antigen) ▪ Approximately 50 percent of the individuals who receive a single injection develop the disease. ▪ Vaccines and bee stings may also trigger this type of reaction. ▪ 1–2 weeks after exposure: fever , rash , arthritis ; proteinuria occurs with renal involvement Serum Sickness Reaction Green venom antigen, Red anti- venom, Blue preformed antibody Disease of Type III Hypersensitivity Autoimmune Disease: Systemic lupus erythematosus (SLE) ▪ Antibodies directed against parts of the nucleus : antinuclear antibodies (ANA), a universal finding in SLE ▪ Ag-Ab complexes deposit in multiple areas: o Skin/mucocutaneous o Kidneys (glomerulonephritis) o Joints (arthritis) o Central nervous system (strokes, seizures) Lab Diagnosis Clinical history and findings (Arthus reaction, serum sickness often diagnosed clinically) Laboratory tests: o CBC o Anemia, thrombocytopenia, leukopenia: SLE o Complement levels (general methods) o Generally found in low levels in associated conditions o Antibodies: ANA, anti-dsDNA Ab. o Latex agglutination test such as RF. o Fluorescent staining of tissue sections. Surgical procedures: renal biopsy, skin biopsy, bronchoscopy Type IV (Delayed-type hypersensitivity) Result from the reactions of T lymphocytes, often against self antigens in tissues. These T cell–mediated diseases represent type IV hypersensitivity, usually a subpopulation of Th1 cells, play the major role in its manifestations. Antibody and complement are not directly involved. A cytokine-mediated process is activated by T-helper cells while cytotoxic T cells directly release cytotoxins to infected or dysfunctional cells, causing cell lysis Does not occur until 24–72 hours after exposure of a sensitized individual (thus, delayed-type hypersensitivity) Physiology T cells are involved. Major types: T-helper (Th) cells CD4+ T cells /Th cells Regulate immune response by secreting cytokines that activate B cells , other T cells , and phagocytes Cytotoxic T cells CD8+ T cells /Tc (cytotoxic or killer T cells) Directly kill cells or utilize cytokines in an immune response Pathogenesis of delayed Hypersensitivity ❖ Sensitization phase: Uptake, processing, and presentation of the antigen (Ag) by APC (DCs and Macrophages) and MHC (class I & II) to activate T cells. ❖ Effector phase: ▪ Cytokine-mediated Ag (on the surface of APCs) is recognized by primed Th cells → APCs produce interleukin (IL- 12), which induce differentiation to Th1 cells Th1 cells produce: o IL-2: increases T-cell production of Th1 cells o Interferon-gamma (IFNγ): recruits macrophages o Tumor necrosis factor (TNF): increases vascular permeability and recruits more leukocytes Release of inflammatory mediators → cellular damage, then tissue injury. Pathogenesis of delayed Hypersensitivity Pathogenesis of delayed Hypersensitivity Pathogenesis of delayed Hypersensitivity Persistent antigen stimulation → granuloma formation o Ag could not be phagocytosed, so the immune system attempts to “wall off the area.” o Macrophages become elongated (epithelioid) and can fuse (Langhans giant cell). o Activated macrophages release lysosomal enzyme, complement components, and reactive oxygen species that cause tissue damage. o More lymphocytes are recruited, with fibroblasts forming a “walled off-ball formation.” ▪ Direct cell cytotoxicity: o CD8+/cytotoxic T cells release cytotoxins → kill targeted cells → tissue injury. Pathogenesis of delayed Hypersensitivity Disease of Delayed Hypersensitivity Disorders typically are chronic and progressive, in part because T cell reactions tend to be prolonged. Allergic contact dermatitis: poison ivy (antigen: urushiol), nickel, perfume, can spread to other parts with antigen transfer by touch. Tuberculin: Intradermal injection of tuberculin, a purified protein derivative (PPD) of the tubercle bacillus. Reaction is generally minimal and short-lived Diabetes mellitus type I: T (CD8+) cells mediate destruction of beta cells in pancreatic. Disease of Delayed Hypersensitivity ❖ Systemic Diseases: Rheumatoid Arthritis (RA): inflammation of the joint Multiple Sclerosis: inflammation of myelin around the nerve fibers Inflammatory Bowel Disease: inflammation in the lining of the intestine Lab Diagnosis Patch test: used to diagnose allergic contact dermatitis, where the allergen is fixed on a patch then applied on skin (back or arm). Then the result read after 2 days and on day 4 or 5. Tuberculosis: is detected by tuberculin test, chest X-ray, and Sputum acid fast bacillus. (AFB) Diabetes Mellitus Type I: is detected by measuring haemoglobin A1c as well as to others lab tests. Thank You