L9L10 Pharmacology of the Immune System PDF

L9L10 Pharmacology of the Immune System Pharmacology of the immune system - and Hypersensitivity reactions Year 2 Drugs and Disease Peter McNaughton [email protected] After these two lectures students should be able to: o understand the basis of innate and acquired immunity o distinguish be...

L9L10 Pharmacology of the Immune System Pharmacology of the immune system - and Hypersensitivity reactions Year 2 Drugs and Disease Peter McNaughton [email protected] After these two lectures students should be able to: o understand the basis of innate and acquired immunity o distinguish between the different types of inflammatory cells and have an understanding of their function o understand the origin of autoimmune diseases and the strategies used to control them o understand how interactions between components of the immune system lead to different types of hypersensitivity reactions o distinguish between the four types of hypersensitivity reactions o identify the mechanisms underlying each of these hypersensitivity reactions o describe the mechanisms of action of drugs used to treat hypersensitivity reactions Background reading: “Pharmacology” Rang et al. Very up to date and probably the best for background reading on this topic. Inflammation 2 Aulus Cornelius Celsus, De medicina, c. A.D. 25: “Notse vero inflammationis sunt quatuor, rubor et tumor cum calore et dolore” – “The true signs of inflammation are four”: Rubor - Redness (increase in local blood flow caused by vasodilator action of inflammatory mediators) Calor - Heat (ditto) Tumor - Swelling (increase in vascular permeability which causes fluid and blood proteins to leak from venules). Dolor - Pain (direct action on the pain-sensitive nerve terminals) "It is not cruel to inflict on a few criminals sufferings which may benefit multitudes of innocent people through all centuries." (De Medicina) Activation of the immune system. Innate immune response Adaptive immune response (acquired immunity) Ready for immediate action Slower in action Relatively nonspecific Specific to particular pathogens The responses of both the innate and the adaptive immune systems contain important targets for drug therapy. Innate – ready for immediate action. Non-Specific. Adaptive immune response – specific to pathogens. Innate Immune System 3 Events in innate immunity Bacteria express on their surfaces molecules (e.g. lipopolysaccharides) not present in mammals. These are called “Pathogen Associated Molecular Patterns” (PAMPs). PAMPs bind to Toll-Like Receptors (TLRs) present in immune cells such as macrophages Occurs in post capillary venules Release of cytokine – interleukin 1 and TNF-alpha (come from macrophages – tissue resident macrophages/sentinels). When a bacterium is detected, the macrophages recognize and engulf the bacterium and release cytokines. Cytokines signal endothelial cells which release chemicals to attract neutrophils. Phagocytes adhere to endothelium and migrate towards bacteria. Bacteria killed by reactive oxygen. Attack of immune system contributes to sepsis. Pus = neutrophils 4 10 toll like receptors. Typical cell signalling cascade involving adaptor proteins IKB releases nuclear factor kappa B (NF-kB) NF-kB enters nucleus and leads to transcription of cytokines. 5 Neutrophils are the first to invade infected tissue Stages of neutrophil entry: Rolling Activation Adhesion Flattening Transmigration Zone of high calcium at front of neutrophil for movement 6 Adaptive immune system Adaptive immune system Antigen engulfed by antigen presenting cell e.g., dendritic cell. Taken up into intracellular vesicles. Dangerous protein cleaved into several pieces 5-10 amino acids long. 7 Antigens presented to t cells. Antigen presenting protein (major histocompatibility complex 2) T cells capable of binding become activated. T cells release cytokine (interleukin 2) which acts back on the same T cell. AKA autokines. Can be targeted by drugs to combat autoimmune diseases. Branches to adaptive immune system (antibody based/b cell and cell based/t cell). Allergies are a special case. On first exposure to an allergen (e.g. pollen) the allergen is ingested by an antigen-presenting cell (see above) to activate a subset of T cells (Th2 cells) releasing IL4 as shown above and thus activating B cells. The antibody synthesized is IgE which can then bind to allergen on subsequent exposure to activate mast cells (sensitized state). IgE critical to allergies 8 Autoimmune diseases Autoimmune diseases Autoimmune diseases are caused when the immune system becomes directed against the body’s own tissues. The initial causative event is likely to be pathogen invasion (perhaps with only mild symptoms), against which an immune attack is mounted, but which expresses a protein with sequence similarity to endogenous proteins. In general the causative pathogen in autoimmune diseases has not been identified. Inflammatory episodes form an important element of the pathology of all these diseases (see Type II – IV hypersensitivity reactions below). Autoimmune diseases caused by immune system attack on body’s own tissues, often triggered by pathogenic infection with proteins similar to endogenous proteins. 9 Females have a more activated immune system than males, which makes them better defended but more likely to suffer from autoimmune diseases. Autoimmune diseases Examples: ØMultiple sclerosis (immune attack on oligodendrocytes) ØType I diabetes (immune attack on pancreatic beta cells) ØRheumatoid arthritis (immune attack on synovium surrounding joints) ØHyper and hypothyroidism (Graves disease and Hashimoto’s thyroiditis respectively) Oligodendrocytes responsible for wrapping myelin around CNS axons. Synovium = tough membrane surrounding joints. 10 Rheumatoid arthritis (RA) Affects proximal phalanges but also feet, spine etc Effects on heart, lungs, kidney, skin, sclera of eye Corticosteroids 11 What are corticosteroids? Corticosteroids are released from the outer layer (cortex) of the adrenal glands. The name glucocorticoids is reserved for endogenous steroids regulating glucose metabolism (hydrocortisone, corticosterone) – corticosteroids includes these plus artificial steroids used in therapy (e.g. dexamethasone, prednisolone). Corticosteroids produce anti-inflammatory effects by inhibiting or activating transcription of genes encoding proteins involved in regulating inflammation. Many genes associated with inflammation are up or down-regulated in most cells of the body. Some clinically used corticosteroids short acting (< 24hrs): intermediate (24-48 hrs): long acting; (>48 hrs): Pro drug = drug precursor 12 hydrocortisone (cortisol, the natural corticosteroid) prednisone, prednisolone (NB prednisone is a prodrug of prednisolone, which is the active steroid) triamcinolone dexamethasone Side effects of steroids: Cushing’s syndrome Immunosuppressive drugs 13 Short-term immunosuppression § High-dose corticosteroids (often I/V). Severe side effects with long-term usage (see Cushing’s syndrome above). § Cyclophosphamide – a prodrug from which the active compound is released in liver. Alkylates DNA and so kills proliferating B, T cells. Severe side effects – hair loss, haemorrhagic cystitis, infertility. Drugs suppress adaptive immune system but not innate immune system. Cyclophosphamide – only used in life threatening conditions due to severe side effects. Alkylates DNA – binds covalently. Prevents process of DNA replication. 14 Longer-term immunosuppression: sites of action of immunosuppressive drugs used in maintenance therapy antibodies to T cell markers resting T lymphocyte early activation cyclosporin tacrolimus IL-2 IL-2R antibodies to IL-2R sirolimus azathioprine mycophenolate late activation proliferation This process is prevented e.g., by cyclosporin and tacrolimus Soil bacteria useful source of drugs to switch off early activation. For transplants: azathioprine and mycophenolate. Immunosuppressant drugs: mechanisms and examples of those used in maintenance therapy antibodies against T cell markers (alemtuzumab) calcineurin inhibitors (cyclosporin, tacrolimus). mTOR (Target Of Rapamycin) inhibitors (sirolimus aka rapamycin) antibodies against IL-2 receptors on T cells (basiliximab) inhibitors of T, B cell proliferation Ø azathioprine – active metabolite inhibits guanosine synthesis and so inhibits DNA synthesis in B, T cells. Other cells obtain guanosine via salvage pathway. Ø mycophenolate – also inhibits guanosine synthesis. 15 ** Basiliximab – against IL 2 receptors Azothioprine and mycophenolate – inhibits guanosine synthesis therefore inhibits DNA synthesis. Alternative pathway for guanosine synthesis. Mast cells – patrol areas exposed to the external world e.g. skin, lungs – the “grenades” of inflammation Inflammation markers Allergy- must be pre-exposed 16 Mast cells are activated by allergens, by complement and by neuropeptides. They release a host of autacoids granule release (prestored) histamine proteases heparin serotonin (5-HT) membrane-derived (on demand) cytokine production (on demand) prostaglandins tumour necrosis factor a (TNFa) leukotrienes Interleukins thromboxane platelet activating factor (PAF) IgE produced against allergens. IgE binds to allergen and Fc receptor when activated. Mast cell contains granules – released during reaction Granule contains histamine, proteases, heparin, and serotonin. ** Cells release cytokines. 17 Histamine and antihistamines Histamine Where is histamine found? Mast cells (in tissues) Basophils (in blood) ECL cells of oxyntic gland in stomach Histaminergic neurons in the CNS Histamine = amino acid. 18 Actions of Histamine contraction of smooth muscle in bronchi, gut dilation of small arterioles – mediated by NO production from endothelial cells (rubor, calor) increased permeability of post-capillary venules via effects on endothelial cells (tumor) sensitizes nerve endings, leading to itching (dolor) injection of histamine response elicits a classical triple response of Lewis: Ø local redness Ø wheal (swelling) Ø red flare from an axonal reflex releasing peptides from nerve endings Increase permeability = swelling. Pathophysiological roles of histamine Involved in various allergic conditions including: allergic rhinitis (hay fever) urticaria (skin rashes) anaphylaxis All are classified as Type 1 hypersensitivity reactions (allergies) - see below 19 Antagonists of the histamine H1 receptor H1: involved in inflammation. Target of ‘antihistamines’ original antagonists e.g. mepyramine non-selective. Actions in the CNS caused drowsiness second generation antagonists eg terfenadine more selective and could not cross the blood-brain barrier but had off-target cardiac effects (block of HERG ion channels leading to ventricular fibrillation – torsades de pointes). third generation antagonists e.g. loratidine and fexofenadine (Allegra) have less CNS action and no action on the heart and are now used widely lack of selectivity useful in other ways eg dimenhydrinate (Dramamine) for treating motion sickness (anticholinergic?). Mepyramine – H1 receptor antagonist and antagonises H2 and H3 in CNS. Terfenadine cannot cross blood brain barrier but has off target cardiac effects. Side effects caused by grapefruit juice. 20 Ventricular fibrillation: torsades de pointes Second-generation H1 antagonists blocked cardiac hERG K+ channels (particularly effectively when concentration was increased by blocking breakdown by P450 liver enzymes – e.g. with grapefruit juice). This could lead to ventricular fibrillation and sometimes to death. Type I - IV hypersensitivity reactions Type 1 – immediate e.g., anaphylaxis, hay fever Type 2 – antibody mediated cytotoxic reactions e.g., drooping eyelid Type 3 – large amount of antibody injected/produced 21 Type 4 – cell mediated/ autoimmune Reminder: adaptive immune system has two main arms - Production of antibodies Cell-based immunity. T cells can Directly attack a cell expressing an antigen Attack a cell “marked” by an antibody Type I hypersensitivity reactions (“allergies” – anaphylactic/immediate) An allergic reaction provoked by an allergen, commonly from the environment. Pollen a common problem. In a sensitized subject allergen binds to circulating IgE which then activates mast cells, releasing a wide variety of mediators. 22 Type I hypersensitivity reactions (“allergies” – anaphylactic/immediate) Immediate hypersensitivity reaction: Occurs in minutes. Release of e.g. histamine, prostaglandins from mast cells. Late hypersensitivity reaction: 2-24 hours. Release of cytokines from mast cells and from other cells such as neutrophils, lymphocytes, macrophages which migrate to the site of entry of the antigen (e.g. lungs, eyes). Examples: allergic asthma, allergic conjunctivitis, allergic rhinitis (hay fever), urticaria (hives), bee-stings, nut allergies, anaphylactic shock. Type I hypersensitivity reactions (“allergies” – anaphylactic/immediate) Treatments: Avoid allergen Injected low-dose allergens to desensitize response Antihistamines (H1 receptor antagonists) Corticosteroids Cromolyn sodium – reduces mast cell activation (“mast cell stabilizer”). Mechanism unknown. Leukotriene receptor antagonists (e.g. montelukast) Epinephrine (adrenaline), injected. Used for emergency treatment of anaphylaxis (“Epi-pen”). Inhibits release of mediators from mast cells Corticosteroids can be administered as a nasal spray to reduce systemic effects. 23 Adrenaline inhibits release of mediators from mast cells due to cAMP release. Type II hypersensitivity reactions (cytotoxic, antibody-dependent) Reaction of the immune system against an antigen adsorbed to the surface of the body’s own cells. Examples include penicillin (bound to red cells) or pathogens adsorbed onto the surfaces of the cells. The antigen can be a body protein (e.g. ACh receptor – myasthenia gravis). Antibodies (IgG and IgM) bind to the foreign antigen. The Fc domains of these antibodies are recognised by natural killer (NK) cells and the cell bearing the foreign antigen is destroyed (antibody-dependent cellmediated cytotoxicity or ADCC). Penicillin allergy = type 2 hypersensitivity reaction. Antibody depended cell mediated cytotoxicity (ADCC) – t cells destroy unwanted foreign antigens on the surface of a self-cell 24 Type II hypersensitivity reactions (cytotoxic, antibody-dependent) Examples: Penicillin binds to red cells which are then recognized as foreign and destroyed by the immune system. Myasthenia gravis (autoimmune attack on the ACh receptor and resulting muscle weakness) Treatments: Avoid allergen (e.g. withdraw penicillin) Corticosteroids (immunosuppressant – see above) Azathioprine (immunosuppressant – inhibits purine synthesis and so inhibits B cell proliferation). Type III hypersensitivity reactions (immune complex-mediated) Excess antigen leads to antigen-immune complexes which can accumulate in tissues, blood vessels etc and initiate an inflammatory reaction. Examples: o “Farmer’s lung” – mould or hay dust causes inflammation of lung alveoli. o “Arthus reaction” after injection of vaccine Treatments: o Avoid allergen o Corticosteroids o Cromolyn sodium (interferes with release of inflammatory mediators from mast cells). Rare Local inflammatory reaction 25 Type IV hypersensitivity reactions (delayed, cell-mediated) Delayed reaction – takes days or weeks to develop. Unlike types II, III it is cell-mediated, not antibody-mediated. Activated T cells bind to and destroy target cells which are presenting an antigen. Many autoimmune diseases fall into this category. Attack carried out by t cells Type IV hypersensitivity reactions (delayed, cell-mediated) Examples: Contact dermatitis Many autoimmune diseases: Type 1 diabetes – immune system attacks pancreatic b cells Multiple sclerosis – immune system attacks oligodendrocytes myelinating CNS neurons Rheumatoid arthritis – immune system attacks synovial membrane in joints Treatments Avoid allergen (in case of contact dermatitis) Corticosteroids Immunosuppressants (ciclosporin, azathioprine, monoclonal antibodies targeting immune system). Contact dermatitis – localised skin inflammation in response to a surface allergen or irritant. 26 The End 27