Immunology (Cytokines) Lecture 6 PDF

Al-Turath University /College of Pharmacy Microbiology II-2nd semester/2nd year students (2023/2024) Assist. Prof. Dr. Shaymaa Abdalwahed Immunology (Cytokines) Lec 6...

Al-Turath University /College of Pharmacy Microbiology II-2nd semester/2nd year students (2023/2024) Assist. Prof. Dr. Shaymaa Abdalwahed Immunology (Cytokines) Lec 6 Cytokines (Definition and properties) ▪ It is Mediators, low molecular (Less than 30 kDa) secreted proteins released by cells. ▪ It is responsible for interactions and communications between cells. ▪ other names include Lymphokine (cytokines made by lymphocytes). ▪ Monokine (cytokines made by monocytes). ▪ Chemokine (cytokines with chemotactic activities). ▪ Interleukin (cytokines made by one leukocyte and acting on other leukocytes). Cytokines are produced de novo in response to an immune stimulus. Cytokines are released by many cell populations, but the predominant producers are helper T cells (TH) and macrophages. Cytokines are nonspecific in their actions, the specificity of an immune response is determined by Ag recognition by B and T cells. Additionally, the half life of cytokines in the bloodstream or other extracellular fluids into which they are secreted is usually very short, ensuring that they act for only a limited period of time. Note: Dalton (Da) is an alternate name for the atomic mass unit, and kilodalton (kDa) is 1,000 daltons. Cytokines Action- include the following: ▪ Autocrine: they can act on the cells that produce them. ▪ Paracrine: they can act on other cells in the immediate vicinity (nearby cell). ▪ Endocrine: they can act on cells at a distance (endocrine) after being carried in blood or tissue fluids. 1 Cytokines Potent ❑ Pleiotropy: cytokine that secret from, or act on more than one cell. ❑ Redundant: similar functions can be stimulated by different cytokines. ❑ Synergistic / antagonistic: Synergy refers to the property of two or more cytokines having greater than additive effects. Antagonism refers to the ability of one cytokine inhibiting the action of another. ❑ Cascade & induction: Cytokines often induce the synthesis of other cytokines resulting in cascades of cytokine activity in which later cytokines may influence the activity of earlier cytokines. Function of Cytokines: Cytokines generally function as intercellular messenger molecules that evoke particular biological activities after binding to a receptor on a responsive target cell. Their function are: 1. Regulate intensity and duration of Immune Responses (IR). 2. Development of both cellular and humoral IR. 3. Stimulate or inhibit the activation, proliferation and differentiation of many cells (T cell, B cell, macrophages, Nk cell and other leukocyte). 4. Regulate the secretion of Abs and other cytokines. 5. Increase expiration of other cytokines. 6. Induction of inflammatory IR. 7. Regulation of hematopoiesis. 8. Heling of wounds. Hematopoietic stem cells (HSCs) continuously replenish/replace all classes of blood cells. Blood cells, which are categorized in either the common lymphoid or the myeloid progenitor, are generated from hematopoietic stem cells (HSCs). I. Common Lymphoid Progenitor cells (CLPs) include T- lymphocyte, B- lymphocyte, and natural killer (NK) cells. II. Common Myeloid Progenitor (CMP) includes: A. Megakaryocytes and Erythrocytes (MegE) progenitor include erythrocyte and platelets. B. Granulocytes and macrophages (GM) progenitor include: 2 1. Myeloblasts immature WBC that form in bone marrow and become mature WBC called granulocyte that include: Neutrophils, Basophils/ mast cell, and Eosinophils. 2. Monocytes include: Macrophage. III. Another cell type, Dendritic Cells (DCs), is not clearly grouped either in lymphoid or myeloid lineage, because DC can be arise from either CLPs or CMPs. Cytokine families include: 1. Hematopoietic family. 2. Interferon family. 3. Tumor necrosis factor (TNF) family. 4. Chemokine family: - I, II, and III elicit physiological responses. - IV serves as a chemoattractant. Cytokine receptor families: There are 5 families of receptor proteins: 1. Immunoglobulin (Ig) superfamily receptors- include: Interleukin (IL)-1, Macrophage colony stimulating factor (M-CSF). 2. Class I cytokine receptor family (hematopoietin receptor family)- include: IL-2, 4,13,15, Granulocyte Macrophage colony stimulating factor (GM-CSF), Granulocyte colony stimulating factor (G-CSF). 3. Class II cytokine receptor family (interferon receptor family)- include: Interferon – γ. 3 4. Tumour Necrosis factor (TNF) receptor family – include: TNF-α, β, Fas, Cluster Differentiation (CD) 40, Nerve growth factor. 5. Chemokine receptor family -IL8, Regulated on Activation Normal T cell expressed and secreted (Rantes), Macrophage inflammatory protein (MIP)-1, Platelet Factor. Cytokine Secretion by TH1 and TH2 Subsets: T helper 1 (TH1) subset (CD4+ T cells) produce IFN-γ has antiviral and antiparasitic activities and also inhibits the proliferation of a number of normal and transformed cells. IFN-γ is act to: 1. IFN-γ activates macrophages, stimulating these cells to increase microbicidal activity. 2. IFN-γ up-regulate the level of class II MHC and is the only interferon that stimulates the expression of these proteins. 3. IFN-γ secrete cytokines such as IL-12, which induces TH cells to induces antibody-class switching to IgG and support phagocytosis and fixation of complement. 4. TNF-β and IFN-γ are cytokines that mediate inflammation. 5. IFN-γ promote the differentiation of Tc CD8+ (IFN-γ induces upregulation of MHC class I molecules which have a pivotal role for host defense against intracellular pathogens) 6. IFN-γ inhibits the expansion of the TH2 population. Note: IFN-γ secretion by T cells is transient, reaching its peak at approximately 24 h after cell stimulation and then returning to baseline levels. All CD8+ T cells are programmed to produce IFN-γ on activation, only TH1-differentiated CD4+ T cells produce IFN-γ efficiently. T helper 2 (TH2) subset: produce- IL-4 and IL-5 and IL-10. 1. TH2 act to eosinophil activation and induces production of IgE and supports eosinophil- mediated attack on helminth (roundworm) infections (act as protective immunity against helminths and other extracellular parasites). 2. TH2 produce IL-4 and IL-10 that suppress the expansion and production of TH1 cell populations. ▪ Typically, the TH1 profile of cytokines is higher in response to intracellular pathogens. ▪ the TH2 profile is higher in allergic diseases and helminthic infections. 4 Cytokine-Related Diseases: 1. Bacterial Septic Shock ▪ Occur in gram-negative bacteria, including E. coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterobacter aerogenes, and Neisseria meningitidis. ▪ Bacterial septic shock is often fatal, and symptoms include drop in blood pressure, fever, diarrhea, and widespread blood clotting in various organs. Bacterial septic shock apparently develops because bacterial cell-wall endotoxins stimulate macrophages to overproduce IL-1 and TNF- to levels that cause septic shock. 2. Bacterial Toxic Shock is Caused by Superantigens ▪ Superantigens bind simultaneously to a class II MHC molecule and to the V domain of the T- cell receptor ▪ Activate large numbers of T cells irrespective of their antigenic specificity. ▪ Bacterial superantigens include several enterotoxins, exfoliating toxins, and toxic-shock syndrome toxin (TSST1) from Staphylococcus aureus. ▪ high levels of TNF and IL-1 is produced. ▪ Cause fever, widespread blood clotting, and shock. 5 3. Lymphoid and Myeloid Cancers ▪ Ex: high levels of IL-6 are secreted by cardiac myxoma cells (a benign heart tumor), myeloma and plasmacytoma cells, and cervical and bladder cancer cells. 4. Chagas’ Disease ▪ Trypanosoma cruzi is the causative agent (parasitic protozoan). ▪ It is characterized by severe immune suppression. ▪ Caused by dramatic reduction in the expression of the 55-kDa α subunit of the IL-2 receptor. ▪IL-2 activates NK cells, CD4, and CD8 T cells and may be necessary to immunity development. Therapeutic Uses of Cytokines Ex: cytokine receptor blockade and the use of cytokine analogs and cytokine-toxin conjugates. Problems with cytokine therapies: ▪ Effective dose levels. ▪ Short half-life (poor pharmacokinetics). ▪ Potent biological response modifiers can cause unpredictable side effects (a narrow therapeutic window). The adaptive immunity acts selectively and specifically. It characterized by: 1 Antigen specificity (highly specific). 2 Diversity. 3 Self/non-self recognition. 4 Immunological memory and can respond rapidly and vigorously to a second antigen exposure. Adaptive (Acquired or Specific) Immunity- Work by two mechanisms: 1) Humoral immune response: - Antibodies are produced by B-lymphocytes. - These have the ability to recognize and bind specifically to antigen that induced their formation. 2) The Cell Mediated Immune response (CMI) - It is mediated by certain types of T-lymphocytes. - T-lymphocytes recognize foreign material by means of surface receptors. - T-lymphocytes attack and destroy foreign material directly or through release of soluble mediators i.e. cytokines. Cells of the adaptive immune system: 1. B cells- is: mature within bone marrow (BM). 6  express Ag-binding receptors, which is a membrane-bond Ab (glycoprotein in nature) molecule. B cells may be activated by an encounter with antigen to become antibody-secreting plasma cells. Each antibody (Ab) consists of four polypeptides– two heavy (H) chains and two light (L) chains joined to form a "Y" shaped molecule. The four chains are covalently linked by disulfide bonds. The Y molecule is composed of two identical halves, each with the same antigen-binding site. (i.e. antibodies with the same antigen-binding sites can have any one of several different tail regions. Each type of tail region gives the antibody different functional properties, such as the ability to activate the complement system, to bind to phagocytic cells, or to cross the placenta from mother to fetus). Ab composed of two different kinds of polypeptide chain: One, of approximately 50 kDa, is termed the heavy or H chain. the other, of 25 kDa, is termed the light or L chain. The amino terminal portion of each H chain participates in the antigen-binding site; the other (carboxyl) terminal forms the Fc fragment, which has various biologic activities (eg, complement activation and binding to cell surface receptors). Therefore, an individual antibody molecule always consists of identical H chains and identical L chains. Antibodies are divided into five major classes, IgM, IgG, IgA, IgD, and IgE, based on their constant region structure and immune function. The binding of antibodies to invading pathogens also recruits various types of white blood cells and a system of blood proteins, collectively called complement (C). The white blood cells and activated complement components work together to attack the invaders. 7 ❑ As predicted by the clonal selection theory, all antibody molecules made by an individual B cell have the same antigen-binding site. ✓ The first antibodies made by a newly formed B cell are not secreted. Instead, they are inserted into the plasma membrane, where they serve as receptors for antigen. ✓ Each B cell has approximately 105 such receptors in its plasma membrane. ✓ Each of these receptors is stably associated with a complex of transmembrane proteins that activate intracellular signaling pathways when antigen binds to the receptor. ✓ Each B cell produces a single species of antibody, each with a unique antigen-binding site. ✓ When a naïve or memory B cell is activated by antigen (with the aid of a helper T cell), it proliferates and differentiates into an antibody-secreting effector cell (e.g. activated lymphocytes and phagocytes). Such cells make and secrete large amounts of soluble (rather than membrane-bound) antibody, which has the same unique antigen-binding site as the cell-surface antibody that served earlier as the antigen receptor. ✓ Effector B cells can begin secreting antibody while they are still small lymphocytes, but the end stage of Effector B cells maturation pathway is a large plasma cell, which continuously secretes antibodies at the astonishing rate of about 2000 molecules per second. 8 The two arms of the immune response, cell mediated and antibody mediated, develop concurrently. In the antibody-mediated arm, helper (CD4) T lymphocytes recognize the pathogen’s antigens complexed with class II MHC molecules on the surface of an APC (eg, macrophage, B cell) and produce cytokines that activate B cells expressing antibodies that specifically match the antigen. The B cells undergo clonal proliferation and differentiate into plasma cells, which then produce specific immunoglobulins (antibodies). Thus, this arm of the immune response is excellent for combating extracellular pathogens and their toxins. Protective Functions of Antibodies: 1. Enhanced Phagocytosis. 2. Virus Neutralization. 3. Neutralization of Toxins 4. Complement-Mediated Lysis. 5. Antibody-Dependent Cell Cytotoxicity (ADCC) In the cell-mediated arm, the antigen–MHC class I complex is recognized by cytotoxic (CD8) T lymphocytes. Each class of T cells produces cytokines, becomes activated, and expands by clonal proliferation. T cells can differentiate into effector cells. ✓ T Cell are lymphocytes and they are called T cells because they mature in the thymus (first they develop in the BM then they travel to thymus). ✓ T Cell can be distinguished from other lymphocytes, such as B cells and natural killer cells (NK cells), by the presence of a T-cell receptor (TCR) on the cell surface. ✓ T Cell do not have antigen-presenting properties (but rather, requiring B cells or macrophages for its antigen-presenting property). There are several subsets of T cells, each with a distinct function: T helper cell (TH cell or CD4 T cell): assist other white blood cells in immunologic processes, including maturation of B cell into plasma cell and memory B cell, and activation of cytotoxic T cell and macrophage. These cells are also known as CD4+ T cell because they express CD4 glycoprotein on their surface. It promotes the development of delayed hypersensitivity and thereby also serves in the defense against intracellular agents, including intracellular bacteria (eg, mycobacteria), fungi, protozoa, and viruses. Helper T cell become activated when they are presented with peptide antigen by MHC class II molecules, which are expressed on the surface of antigen presenting cells (APCs). Once activated, they divided rapidly and secrete small protein called cytokines that regulate or assist in the active immune response. 9 Cytotoxic T cell (Tc cell or CTLs or CD8+ T cell): destroy virally infected cells and tumor cells, and are also implicated in transplant rejection. These cells are also known as CD8+ T cell since they express the CD8 glycoprotein at their surface. These cells recognize their targets by binding to antigen associated with MHC class I. Memory T cells: are a subset of antigen-specific T cells that persist long-term after an infection has resolved. They quickly expand to large numbers of effector T cells upon re-exposure to their cognate antigen, thus providing the immune system with “memory” against past infections. Regulatory T cells (Treg cells), formerly known as suppressor T cells, are crucial for the maintenance of immunological tolerance. Their major role is to shut down T cell-mediated immunity toward the end of an immune reaction and to suppress auto-reactive T cells that escaped the process of negative selection in the thymus. Treg cells contribute to immune homeostasis by maintaining unresponsiveness to self-antigens and suppressing exaggerated immune responses. ❖All T cells originate from haematopoietic stem cells in the bone marrow. ❖Haematopoietic progenitors derived from haematopoietic stem cells populate the thymus and expand by cell division to generate a large population of immature thymocytes. ❖The earliest thymocytes express neither CD4 nor CD8, and are therefore classed as double- negative (CD4-CD8-) cells. ❖As they progress through their development they become double-positive thymocytes (CD4+CD8+) ❖ and finally mature to single-positive (CD4+CD8- or CD4-CD8+) thymocytes that are then released from the thymus to peripheral tissues. Both adaptive & innate immunity are work together e.g. Phagocytic cells which are important in the non-specific immune response involve in the activation of T cells. Antigens can be bound by macrophages and dendritic cells. These act as antigen presenting cells. These APCs belong, as lymphocytes, to the exclusive group of immune cells that express in their membranes MHC II (every nucleated cell presents MHC I, but only APC express MHC II). Thus, they are the only cells able to present antigens (epitopes) to the helper T lymphocytes CD4 +. Inflammatory mediators are important in recruitment of specific immune cells, at the same time the specific immune response will act to regulate the intensity of the inflammatory response. 10 Thank You 11