• An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. • Detects a wide variety of agents, from viruses to parasitic worms. • Needs to distinguish them from the organisms own healthy cells and tissues. • Detection is complicated as pathogens can evolve rapidly, producing adaptations that avoid the immune system.
Layered defense The immune system protects organisms from infection with layered defenses of increasing specificity.physical barriers prevent pathogens such from entering the organism.If a pathogen breaches these barriers, the innate immune system provides an immediate, non-specific response. If pathogens successfully evade the innate response, vertebrates possess a third layer of protection, the adaptive immune system, activated by the innate response. Specific and has an immunological memory so immune system mount faster and stronger subsequent attacks.
Components of the immune system Innate immune system Adaptive immune systemExposure leads to Lag time betweenimmediate maximal exposure and maximalresponse responseCell-mediated andhumoral Cell-mediatedandcomponents humoral componentsNo immunological Exposure leads tomemory immunological memoryResponse isnon-specific Pathogen andantigen specific responseFound in nearlyall forms Found only invertebratesof life
CYTOKINES• Definition: Cytokines are soluble hormone-like proteins that allow for communication between cells and the external environment. The term cytokine, or immunocytokine, was used initially to separate a group of immunomodulatory proteins, called also immunotransmitters, from other growth factors that modulate the proliferation and bioactivities of non- immune cells .
The cytokines are important components of the immune system. They act in concert with specific cytokine inhibitors and soluble cytokine receptors to regulate thehuman immune response. Their physiologic role in inflammation and pathologic role in systemic inflammatory states are now well recognized.
• Cytokines are secreted by white blood cells as well as variety of other cells (fibroblasts, endothelial cells, epithelial cells, etc.) in response to inducing stimuli, and are not constitutively expressed. Cytokines comprise: (1) Interleukins initially thought to be produced exclusively by leukocytes, • (2) Lymphokines, initially thought to be produced exclusively by lymphocytes,• (3) Monokines initially thought to be produced exclusively by monocytes,
• (4) Interferon, initially thought to be involved in antiviral responses. • (5) colony stimulating factors, initially thought to support the growth of cells in semi-solid media. • (6) Chemokines thought to be involved in Chemotaxis, and a variety of other proteins and tumor necrosis factor (TNF).• The term Type-1 cytokines refers to cytokines produced by Th1 cells while Type-2 cytokines are those produced by Th2 cells. Type-1 cytokines include IL2, IFN-γ, IL12 and TNF-beta, while Type-2 cytokines include IL4, IL5, IL6, IL-9, IL10, and IL13 .
• It has been shown that a number of viral infectious agents exploit the cytokine repertoire of organisms to evade immune responses of the host. Virus-encoded factors appear to affect the activities of cytokines in at least four different ways: • (1) by inhibiting the synthesis and release of cytokines from infected cells;• (2) by interfering with the interaction between cytokines and their receptors.
• (3) by inhibiting signal transmission pathways of cytokines. • (4) and by synthesizing virus-encodedcytokines that antagonize the effects of host cytokines mediating antiviral processes. • An imbalance in cytokine production or cytokine receptor expression and/or dysregulation of a cytokine process contributes to various pathological disorders.
:properties of cytokines **• Cytokines are short-lived and may actlocally either on the same cell secreted it (autocrine), on other cells (paracrine) or like hormones they may act systemically (endocrine)
Cytokines interact in a network by: • a- including each other (cascade-like activity) • b- transmodulating cytokine cell surface receptors • c- interacting synergistically, additively or antagonistically on cell function - cytokines are nonspecific and antigen-independent in mode of activity
All cytokine receptor have thetypical receptor structure: an extra cellular domain, single membrane- spanning domain & a cytoplasmic domain. • Cytokines may exhibit considerable overlap in their biologic effects on lymphoid, myeloid & connective tissue
classifications of **: cytokines• 1- proinflammatory cytokines:- make the disease worse because they produce fever, inflammation, tissue destruction & sometimes shock & death including IL-1, IL-6, IL-12 & GM-CSF G-CSF, IFN-γ & TNF- α
Anti-inflammatory -2:cytokines • Potent activators of B- Lymphocytes. Include IL-1 receptor antagonist, IL-4, IL-6, IL-11 & IL-13. • They are anti-inflammatory cytokines by their ability to suppress genes for proinflammatory cytokines such as IL-1, TNF & chemokines.
3- Growth factors:• Such as platelet-derived growth factor (PDGF), transforming growth factor-β(TGF-β) & Epidermal growth factor (EGF) influence the proliferation of many structural cells such as fibroblasts & airway smooth muscle cells.
Functional Categories of **Cytokines Cytokines classified according to their biologic actions into three groups: 1) Mediators and regulators of innate immunity - Produced by activated microphages and NK cells in response to microbial infection. - they act mainly on endothelial cells and leukocytes to stimulate the early inflammatory response to microbes.
2) Mediators and regulators of acquired immunity: - Produced mainly by T lymphocytes in response to specific recognition of foreign antigens.- They include IL-2, IL-4, IL-5,, IL-13, IFN, Transforming growth factor-β (TGF-β) and lymphotoxin (TNF- β). 3) Stimulators of haematopoiesis: - Produced by bon marrow, stormal cells, leukocytes. - Stimulate growth and differentiation of leukocytes. - Stem cell factor, IL-3, IL-7, GM-CSF.
(Interferons (IFNs* Interferons (IFNs): are proteins secreted in response to viral infections or other stimuli * They include: - INF-α produced by leucocytes induced by virus infected cells - INF-β produced by fibroblasts - INF-γ produced by NK cells,TH1 cells, CD8 T-cells
: Action of INF-α and IFN-β - Prevent viral replication- Increase MHC-I expression on viral infected cells helping their recognition by CD8 T cells - Increase cytotoxic action of Nk cells - Inhibit cell proliferation and tumor growth
: Action of IFN-γ • Activate Macrophages. • Increase expression of MHC-I and II on APCs. • Enhance cytotoxic actions of Nk cells. • Promote production of TH1 and inhibits proliferation of TH2.
summary of selected cytokines **Cytokine ActionsIL-1 NK cells -Attract Enhance activity of- neutrophil¯ophageIL-2 antigen-primed Induce proliferation of- T-cells NK cells Enhance activity of-IFN-γ macrophages & NK enhance activity of - cells - increased expression ofMHC molecules - enhance production of IgG2aIFN-α cytotoxic effect ontumor cells - induces - cytokine secretion in the inflammatory response
:Immune activation cascade ** 1- Signal-1APC activates specific receptors on outer surface of T- cell (CD3) 2- Signal-2 : Costimulation of CD80:86 on APC to T-lymphocytes 3- Signal-3: Activation of different cellular pathway in T-cells themost important is calcium calcineurin pathway where intracellular Ca++ activates calcineurin.
Activated calcium calcineurin activates inactive (phosphprylated) NFATc into activated (dephosphorylated) NFATc 4- Signal-4 NFATc associates with other nuclear factors leading to activation of genes encoding cytokines5- gene expression leads to IL-2 & IL-2 receptors release 6- IL-2 activates lymphocytes proliferation
Immunosuppressive drugs ** Immunosuppressive drugs can be categorized according to their mechanism of action to: • Some agents interfere with cytokines production or action. • Others disrupt cell metabolism , preventing lymphocyte proliferation .• Mono- or polyclonal antibodies block T-cell surface molecules.
- Earlier immuno-suppressant suppress both humoral & cell mediated immunity but recent drugs suppress lymphocyte function by drugs or antibodies aginst immunoproteins. - No single agent is used but 2-4 combination drugs or agent with different mechanisms of actions which disturb various level of T—cell activation.
I- selective inhibitor of cytokine:production & function A) Cyclosporine: ** Source & nature: - lipophilic cyclic polypeptide extracted from soil fungus ** Uses: 1 - Prevent rejection of kidney, liver & cardiac allogeneic transplants: Prevent acute phase rejection specially when taken with corticosteroids & mycophenolate mofetil. 2- Alternative to methotrexate for severe active rheumatoid arthritis. 3- In patient with psoriasis not respond to other drugs.
:mechanism of action ** Cyclosporine enters T- lymphocyte to bind with cyclophillin forming complex which binds to & inhibits calcineurin that responsible fordephosphorylation & activation of NFATc (cytosolic Nuclear Factor of Activated T-cell) so this NFATc cannot enter the nucleus so decrease production of IL-2 & IL-2 receptors essential for proliferation of T- cells.
** Pharmacokinetics: - Oral or I.V infusion- Hepatic metabolism by CYP3A4 to inactive metabolites excreted billiary ** Adverse effects: - Nephrotoxicity: irreversible in 15% of patients - Hepatotoxicity - Viral infection due to herpes group or cytomegalovirus (CMV) - Anaphylactic reactions on parentral administration- Hypertension, hyperlipidema , hyperkalemia, hirsutism & gum hyperplasia
:(B( Tacrolimus : (FK506 Differs from cyclosporine in the following: 1- Preferred than cyclosporine due to : a- more potent. b- lower dose of corticosteroids is needed so less toxicity. c- ointment preparation has been approved for moderate to severe atopic dermatitis. 2- Mechanism of action as cyclosporine but bind to different immunophyllin (FK-binding protein (FKBP1-2) ) .3- Pharmacokinetics: as cyclosporine but better bioavailability. 4- Adverse effects: Mainly neurotoxic & insulin dependent diabetes mellitus but less C.V.S toxicity & no hirsutism or gum hyperplasia.
( C( Sirolimus: (earlier name rapamycin ** Source & nature: Macrolide obtained from fermentations of soil mold. ** Uses:1-In combination with cyclosporine & corticosteroids in renal transplantation values: a- lower doses of drugs so less toxicity. b- combination of CsA & SRL has synergistic effect as SRL acts later in immune activation cascade . N.B) to limit toxicity of CsA, SRL usually is used during calcineurin inhibitor withdrawal protocols. 2- Due to its anti-proliferative effect: SRL-coated stents inserted into cardiac Vasculature inhibit restenosis of blood vessels by ↓ proliferation of endothelial cells.
** Mechanism of action: • Binds to the same cytolpasmic binding protein of TAC ( KFBP) but not form complex with calcineurin but form complex with mTOR ( mammalian target of rapamycin) • mTOR is kinase enzyme responsible for: a- T-cell proliferation by promote transmission of cells from G1 to S phase of cell cycle b- DNA repair c- Regulator in protein translation binding of SRL to mTOR inhibits T-cell proliferation
N.B) CsA & TAC inhibits IL-2 production while SRL inhibits IL-2 function ** Adverse effects: • Hyperlipidemia • Headache • Leucopenia • Thrombocytopenia • Impaired wound healing
II- Immunosuppressiveantimetabolites : Usually used in combination with corticosteroids & calcineurin inhibitors CsA & TAC : A- Azathioprine: ** mechanism of action: Prodrug converted to 6-mercaptopurine (6-MP) then to corresponding nucleotide, thioinosinic acid which interferes with purines synthesis which are essential for proliferation of lymphocytes. ** was widely used in organ transplantation. ** adverse effects: - Bone marrow suppression - nausea & vomiting ** Captopril & cotrimoxazole exaggerate leukopenic response while allopurinol inhibit the metabolism of azathioprine .
B- Mycophenolate mofetil ( MMF(: - Replace azathioprine in organ transplantation because it is more safe & more efficacious. ** Mechanism of action: Potent reversible uncompetitive inhibitor of inosine monophosphate dehydrogenase so blocking the de novo formation of guanosine phosphate so deprive proliferating T- & B-cells of a key precursor required for nucleic acid synthesis. ** Adverse effects: • diarrhea , nausea & vomiting • abdominal pain, leucopenia & anemia • higher risk of CMV infection
C- Enteric coated:mycophenolate sodium In order to minimize gastrointestinal effects associated with MMF so used delayed release formulation of active drug mycophenolic acid
** Mono- and Poly-clonal Antibodies Prepared by either immunization of rabbits or horses with human lymphoid cells (producing a mixture of polyclonal antibodies directed against a number of lymphocyte antigens) or by hybidroma technology ( producing antigen-specific, monoclonal antibodies)
N.B) Recombinant DNA technology can also be used to replace part of the mouse gene sequence with human genetic material thus humanizing antibodies produced. Replace of FC portion of animal antibodies by human FC region not affect on antigen specificity.N.B) The name of monoclonal antibodies contain muro if they are from murine (mouse) source and xi or iz if they are humanized.
A( Antithymocyte globulins :((ATG • Thymocytes are developed from thymus and acts as precursors of T-cells.• ATG prepared by immunization of large rabbits or horses with human lymphoid cells so considered polyclonal. • Rabbit is usually preferred than horses as more potent.
- The produced antibodies bind to surface of circulating T-lymphocytes which then undergo complement mediated destruction or antibody-dependent cytotoxicity or apoptosis. - ATG used with immunosuppressive drugs at time of transplantation to prevent early phase of graft rejection.Also used to treat severe rejection episodes in corticosteroids-resistant cases. N.B) Because humoral mechanism still active antibodies can be formed against these foreign protein.
Monoclonal antibodies: Monoclonal antibodies (mAb or moAb) are monospecific antibodies that are the same because they are made by identical immune cells that are all clones of a unique parent cell. This has become an important tool in biochemistry, molecular biology and medicine. When used as medications, the non- proprietary drug name ends in –mab.
: Production Hybridoma cell production:Monoclonal antibodies are typically made by fusing myeloma cells with the spleen cellsfrom a mouse that has been immunized with the desired antigen. However, recent advances have allowed the use of rabbit B- cells. Polyethylene glycol is used to fuse adjacent plasma membranes, but the success rate is low so a selective medium in which only fused cells can grow is used.
• This mixture of cells is then diluted and clones are grown from single parent cells on microtitre wells. The antibodies secreted by the different clones are then assayed for their ability to bind to the antigen (with a test such as ELISA or Antigen Microarray Assay). The most productive and stable clone is then selected for future use.• The hybridomas can be grown indefinitely in a suitable cell culture media, or they can be injected in mice (in the peritoneal cavity, the gut), they produce tumors containing an antibody-rich fluid called ascites fluid.
Recombinant: • Recombinant antibody engineering involves the use of viruses or yeast to createantibodies, rather than mice. These techniques rely on rapid cloning of immunoglobulin gene segments to create libraries of antibodies with slightly different amino acid sequences from which antibodies with desired specificities can be selected
• Humanized monoclonal antibodies that acts on the HER2neu (erbB2) receptors. • As inhibition of cell growth by trastuzumab is limited to HER2- positive cancers, testing tumors for HER2 expression became integral to selecting patients • HER2 testing of breast cancer patients becomes a routine
Uses:Herceptin is used mainly to treat women with breast cancer. It may be used in the early stages to increase the chances of a cure. It also used in metastatic breast cancer. In most cases it is used in combination with chemotherapeutic agents paclitaxel or docetaxel.
• Cetuximab attaches to the EGFRs and prevents the receptors from being activated. • This stops the cells from dividing. therefore stop the cancer cells from growing. • Cetuximab also make the cancer cells moresensitive to chemotherapy and radiotherapy• Tests may be done to find the level of EGFR in the tumour cells before cetuximab is given.
IMMUNOSTIMULATIO N• In contrast to immunosuppressive agents that inhibit the immune response, a few immunostimulatory drugs have been developed with applicability to infection, immunodeficiency, and cancer. • Problems with such drugs include systemic (generalized) effects at one extreme or limited efficacy at the other.
• LevamisoleIt was synthesized originally as an anthelmintic but appears to "restore" depressed immune function of B-lymphocytes, T-lymphocytes, monocytes, and macrophages. Its only clinical indication is as adjuvant therapy with 5-fluorouracil after surgical resection in patients with stage C colon cancer, where it occasionally has been associated with fatal agranulocytosis.
•Thalidomide Known for the severe, life-threatening birth defects it caused when administered to pregnant women. For this reason, it is available only under a restricted distribution program and can be prescribed only by specially licensed physicians who understand the risk of teratogenicity if thalidomide is used during pregnancy. Thalidomide should never be taken by women who are pregnant or who could become pregnant while taking the drug.
• It is indicated for the treatment of patientswith erythema nodosum leprosum and also is used in conditions such as multiple myeloma. Its mechanism of action isunclear. Reported immunologic effects vary substantially under different conditions. For example, thalidomide has been reported todecrease circulating TNF-α in patients with erythema nodosum leprosum, severe refractory rheumatoid arthritis.
• Bacillus Calmette-Guerin (BCG(:Live bacillus Calmette-Guerin is an attenuated, live culture of the bacillus of Calmette and Guerin strain of Mycobacterium bovis, that induces a granulomatous reaction at the site of administration. By unclear mechanisms, this preparation is active against tumors and is indicated for treatment and prophylaxis of carcinoma in situ of the urinary bladder Adverse effects include hypersensitivity, shock, chills, fever, malaise, and immune complex disease.
Recombinant Cytokines Interferons: Although interferons (alpha, beta, and gamma) initially were identified by their antiviral activity, these agents also have important immunomodulatory activities: • Induction of certain enzymes. • Inhibition of cell proliferation. • Enhancement of immune activities, including increased phagocytosis by macrophages and augmentation of specific cytotoxicity by T lymphocytes.
• Recombinant interferon alfa-2b (IFN-alpha 2, INTRON A)Produced and secreted by cells in response toviral infections and other inducers. Interferon alfa-2b is indicated in the treatment of a variety of tumors, including hairy cell leukemia, malignant melanoma, follicular lymphoma, and AIDS-related Kaposis sarcoma. It also is indicated for infectious diseases, chronic hepatitis B & in combination with ribavirin for treatment of chronic hepatitis C.
• Side effects: Flu-like symptoms, including fever, chills, and headache, are the most common adverse effects after administration. Other adverse reactions involving the cardiovascular system (hypotension, arrhythmias, and rarely cardiomyopathy and myocardial infarction) and CNS (depression, confusion) are less-frequent side effects.
• Interferon beta-1a (AVONEX, REBIF), and interferon beta-1b (BETASERON), have antiviral and immunomodulatory properties. They are FDA approved for the treatment of relapsing and relapsing-remitting multiple sclerosis to reduce the frequency of clinical exacerbations . The mechanism of their action in multiple sclerosis is unclear. • Flu-like symptoms (fever, chills, myalgia) and injection-site reactions have been common adverse effects.
**Tumor necrosis factor (TNF α ( inhibitors : • Infliximab: A monoclonal antibody against tumor necrosis factor alpha (TNFα). Infliximab was approved by the U.S. Food and Drug Administration (FDA) for the treatment of psoriasis, Crohns disease, ankylosing spondylitis, psoriatic arthritis,rheumatoid arthritis and ulcerative colitis.
EtanerceptEtanercept is a dimeric molecule, and this dimeric structure is necessary for its proper therapeutic activity. To reduces the effect of naturally present TNF, and hence is a TNF inhibitor, functioning as a decoy receptor that binds to TNF.
Drug allergy **(immunological reactions to:(drugs • Drug reactions mediated by immune responses may have different mechanisms thus any of the four major types of hypersensitivity can be associated with allergic drug reactions: Type I: • IgE-mediated acute allergic reactions to stings, pollens, & drugs including anaphylaxis, urticaria, angioedma. IgE is fixed to tissue mast cell.
• Type II: Drugs modify host proteins eliciting antibody responses to modified protein. These allergic response involve IgG& IgM in which the antibody become fixed to a host cell which is then subject to complement-dependent lysis or to antibody-dependent cellular cytotoxicity. • Type-III:Drugs may cause serum sickness which involves immune complexes containing IgG & is multisystem complement-dependent vascuilitis that may result in urticaria.
• Type-IV: Cell-mediated allergy is the mechanism involved in allergic contact dermatitis from topicallyapplied drugs or induration of the skin at site of an antigen injected intradermally.