IMS - Cytokines

CYTOKINES 

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small soluble proteins that regulate the immune system, orchestrating both innate immunity and the adaptive response to infection Chemical messengers that influence the activities of  other cells.

ACTIONS OF CYTOKINES Autocrine – affecting the same cell that secreted it Paracrine – affecting a target cell in close proximity Endocrine - systemic   

FEATURES OF CYTOKINES 

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Pleotropism single cytokine has many different actions Redundancy different cytokines often have very similar effects Act in networks stimulate the release of other cytokines Act as growth factors for hematopoietic cells modulate the number and composition of cells

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CYTOKINES IN INNATE IMMUNITY Non-immune (Type 1) Interferons IFN-α, IFN-α, IFNIFN-β Tumor Necrosis factor Interleukins IL-1, IL-6, IL-10 , IL-12, IL-15 Chemokines C-X-C, C-C, C subgroup 

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TYPE 1 INTERFERONS 

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ROLES OF CYTOKINES Innate immunity Adaptive immunity Growth and differentiation of immature leukocytes 

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CATEGORIES/FAMILIES Tumor Necrosis Factor Chemokines Interferons Hematopoietic Factors

Colony-stimulating Colony-stimulating Factors Stimulate hematopoietic hematopoietic progenitor cells to form colonies (G-CSF, GM-CSF) Transforming Growth Factors Products of virally transformed cells Induce phenotypic transformation in nonneoplastic cells

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IFN-α IFN-α Produced by mononuclear mononuclear phagocytes IFN-β IFN-β Produced by fibroblasts * Viral infection may produce these molecules Induce expression of proteins that inhibit viral replication Inhibits cell proliferation They bind to same receptor They increase the ability of NK cells to kill virally infected c ells Enhance expression of MHC class I molecules

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TUMOR NECROSIS FACTOR  Triggered by the lipopolysaccharide from gramnegative bacteria Bound by a specific LPS-binding protein that binds to a receptor on mononuclear phagocytes CD14 IL-1, IL-6 In low concentration it acts on leukocytes and endothelium to induce acute inflammation At moderate concentrations it mediates the systemic effects of inflammation IL-1, IL-6, IL-8 High concentrations leads to metabolic alterations and shock 

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TUMOR NECROSIS FACTOR  Principal mediator of the acute inflammatory response to gram-negative bacteria and other infectious microbes Stimulates gene transcription or induces apoptosis TNF α and TNF β share similar activities Stimulate the recruitment of neutrophils and monocytes to sites of infection Activate these cells to eradicate microbes 

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CHEMOKINES Stimulate trans-endothelial leukocyte movement from the blood to the tissue site of infection and regulate the migration of PMNs and mononuclear leukocytes within tissues 

INTERLEUKINS Modulate inflammation and immunity by regulating growth, mobility and differentiation of lymphoid cells Each interleukin functions through a separate receptor system and a distinct molecule by gene cloning and sequencing 

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INTERFERONS Discovered in virally infected cultured cells Enhances expression of specific genes, inhibiting cell proliferation, and augmenting immune effector cells Antiviral agents, immunomodulators, immunomodulators, antineoplastic agents  

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INTERLEUKIN-1 Produced by macrophages and monocytes in response to bacterial LPS and TNF Pro-inflammatory cytokine Induces IL-2 and IL-2 receptor(CD25) in T-cells, proliferation and differentiation of B-cells Enhancement Enhancement of cytotoxicity of NK cells Two types (α,β) (α,β) α type – possesses activity without further processing β type – require cleavage before its functional 

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INTERLEUKIN-6 Appears after IL-1 has been triggered Primary mediator of acute phase response Signal for enhanced fibrinogen synthesis Growth factor to activated B-cell and plasma cell Synergist with IL-3 to promote growth of  hematopoietic progenitor cells and activation and generation of T-cytotoxic cells     

HEMATOPOIETIC FACTORS 

Stem cell Factor it acts on immature stem cells, needed to make Bone Marrow stem cells responsive to other CSF

CHEMOKINES CC chemokine Attract mononuclear cells to sites of chronic inflammation (MCP-1) 

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CXC chemokine Attracts PMNs to sites of inflammation, activates monocytes and may direct the recruitment of  these cells to vascular lesions (CXCL8) CX3 chemokine Forms a cell-adhesion receptor capable of  arresting cells under physiologic flow conditions

INTERLEUKIN-10 Inhibits production of pro-inflammatory cytokines by mononuclear phagocytes Inhibits the accessory functions of mononuclear mononuclear phagocytes for T-cell activation

Antigens and the Major Histocompatibility Complex Antigens a substance that reacts with antibody of sensitized cells but may or not may provoke an immune response. 

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INTERLEUKIN-12 Triggers secretion of IFN-γ IFN- γ by T-cells T-cells and NK cells Promotes differentiation of T-helper1 to secrete IFNγ Enhances the cytotoxic function of NK cells CD8+ T cells  

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Immunogen a macromolecule capable of eliciting the formation of  immunoglobulins or sensitized cells in an immunocompetent immunocompetent host 

Factors Influencing the Immune Response Age Dose Route of Inoculation Health status of the host Genetics     

INTERLEUKIN-15 Release occurs in response to viral, LPS, or other pathogens Supports the development of NK cells 

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Traits of Immunogens Foreignness Macromolecular size Chemical composition and molecular complexity The ability to be processed and presented with MHC molecules   

CYTOKINES IN SPECIFIC IMMUNITY 

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Th1 cytokines IL-2, IFN-γ IFN-γ Th2 cytokines IL-4, IL-5, IL-10

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Foreignness The immunogen must be recognized as foreign or non-self to induce immune response The greater the difference the greater the immune response 

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IFN-Γ IFN-Γ 

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stimulates antigen presentation by MHC I and MHC II molecules Strong stimulator of macrophages and boosts their tumoricidal activity

INTERLEUKIN-2 T-cell growth factor drives the growth and differentiation of both T and B cells and induces lytic activity in NK cells

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The larger the molecule, the more immunogenic. The number of epitope increases proportionally with the size of the molecule. Potent Antigen should be greater than 10,000 daltons

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INTERLEUKIN-4 Triggers activation, proliferation and differentiation differentiation of B-cells Responsible in allergic r eactions, parasitic infections and autoimmune diseases

Parts of an Antigen 

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TUMOR NECROSIS FACTOR Β FACTOR  Β Formerly called as lymphotoxin Binds to a scpecific receptor and triggers apoptosis of the target cell Short-lived and localized

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CYTOKINE ANTAGONISTS

Chemical composition and Complexity  

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Antagonists Exist In 2 Forms Receptor Antagonists (Bind Receptor, No Activation) Bind Cytokine (Prevent Cytokine From Binding Receptor) Well Studied Example: IL1Ra In Many Cases Antagonist Is A Soluble Receptor Derived From Proteolytic Cleavage Of  Extracellular Domain Of Particular Receptor IL-2, IL-4, IFN-γ IFN-γ, IFN-α IFN-α Viruses Produce Cytokine Mimics Or Cytokine Binding Proteins Ex. Poxviruses Produce IL-1-Binding Protein And TNF-binding-protein These Agents Offer Viruses An Advantage

Carrier Portion Protein in nature High molecular weight Immunogenic Epitope Key portion (determinant site) small part of the immunogen that is actually recognized in the immune response Can be linear or conformational

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Proteins - the best and strongest antigen Polysaccharides - ex. endotoxin, pneumococcal capsule Glycoproteins - like ABO, Rh antigens Polypeptide - ex. Insulin Nucleic Acids and Lipids - Least Immunogenic

The ability to be processed and presented with MHC molecules 

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Involves enzymatic digestion to create small peptides or pieces that can be complexed to MHC molecules to present to r esponsive lymphocytes Macromolecule can’t be degraded and presented with MHC molecules, then it would be a poor immunogen

Hapten 

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An incomplete antigen; not immunogenic by itself  but when coupled by a carrier protein can elicit an immune response Complexed artificially with carrier molecules in a laboratory setting, or this may occur naturally within a host and set off an immune response

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Regulate the immune response and play a role in graft rejection bring antigen to the cell surface for recognition by T cells Genes coding for the MHC molecules in humans are found in the short arm of chromosome 6 Synthesized in the rough endoplasmic reticulum Referred to humans as Human Leukocyte Antigen

Types of Antgens 

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Autoantigens - antigens derived from the same individual. Alloantigens - derived from the body of other individuals of the same species. Heteroantigens - derived from other species. Heterophile antigensantigens - those that exist in unrelated plants or animals but which are either identical or closely related in structure so that that antibody to one will crossreact with antigen of the other. Ex. Polysaccharide type XIV of pneumoncoccus reacting with anti-A antisera

Genes coding for the MHC molecules Found on the short arm of chromosome 6 Divided into classes (I, II, III) Each class is found on different locations or loci   

Class I  

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Adjuvants Substances added to an immunogen to enhance immune response prolongs the retention time of the immunogen in the body increases the effective size of immunogen stimulates the influx of macrophage and/or lymphocytes 

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Class II  

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Examples of Adjuvant Freund’s Complete Adjuvant Water in oil emulsion of Mycobacteria butyricum or Bordetella pertussis Lipopolysaccharides Alum Adjuvants  

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Loci – A, B, C Highest on lymphocytes and low or undetected on liver hepatocytes, neural cells, muscle cells, and sperm Glycoprotein dimer ( α, β2-microglobulin) β2-microglobulin) Non-classical antigens ( E, F, G) Presents antigen to CD8+ T-cytotoxic cells

Loci – DP, DQ, DR Found primarily on antigen-presenting antigen-presenting cells, which include B lymphocytes, monocytes, macrophages, macrophages, and dendritic cells Glycoprotein dimer (α, β) Non-classical antigens ( DO, DM, DN) Presents antigen to CD4+ T-helper cells

Class III Genes which code for complement proteins and cytokines such as Tumor necrosis factor Not expressed on cell surfaces 

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Antigen Presentation Thymus dependent antigen Capable of mounting immune response provided there’s assistance from T cells Capable of stimulating B cells Capable of inducing production of memory cells Can induce B cell to form different immunoglobulin classes Examples: viral hemagglutinin, hemagglutinin, diphtheria toxin, PPD

Thymus Independent antigen Can mount immune response without the help from Thelper cells

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Capable of stimulating B cells Not capable of inducing proliferation of memory cells Only IgM can be produced

Examples: Type 1: bacterial polysaccharide, Brucella abortus Type 2: pneumococcal polysaccharide, salmonellapolymerized flagellin,hapten flagellin,hapten conjugated ficoll (polysucrose), dextran

AFFINITY - the strength of the attraction between an epitope and the antigen combining site of the antibody AVIDITY - refers to the strength of interaction between complex antigens

Major Histocompatibility Complex Genes that control expression of a large group of  proteins 

Class II HLA Effective for exogenous antigens Bacteria

Presented in CD8+ Tcytotoxic cells

Presented in CD4+ Thelper cells

Proteasomes

Invariant chain , Invariant chain peptide

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Affinity vs. Avidity 

Class I HLA Effective for endogeneous antigens Tumors Viruses Parasites 

Transporting peptides TAP1 TAP2  

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The highly polymorphic genes within the MHC gene segment of DNA code for a wide range of cell surface structures that T cells must recognize in association with foreign antigen for a successful immune response.

MHC Restriction or MHC Restricted Recognition The process whereby the MHC control interactions between cells. It involves the recognition of foreign antigen in associaiton with Class I or Class II molecules. Antigen Presentation T and B cell cooperation Cytotoxic T cell interaction with target cells HLA Typing 

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Tissue/Organ Transplantation Transplantation Disease Association Paternity Testing Studies of Racial Ancestry and Migration Forensic Medicine

Methods    

Lymphocytotoxicity Test Polyspecific Reagent Mixed-lymphocyte Reaction PCR