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Term Paper on Cytokines
Term Paper Contents:
- Term Paper on the Introduction to Cytokines
- Term Paper on the Process and Classification of Cytokines
- Term Paper on the Properties of Cytokines
- Term Paper on the Detection of Cytokines
- Term Paper on the Cytokine Receptors
- Term Paper on the Clinical Application of Cytokines
Term Paper # 1. Introduction to Cytokines:
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Cytokines (Greek cyto – cell; and, kinos – movement) are small cell-signaling protein molecules. “Cytokine” refers to the immuno-modulating agents, such as interleukins and interferons. Cytokines are secreted by the cells of the immune system and glial cells of the nervous system and are used extensively in intercellular communication. Cytokines can either be proteins, peptides or glycoproteins. All nucleated cells and especially endothelial cells, epithelial cells and macrophages are potent producers of IL-1, IL-6, and TNF-α. Cytokine is a small protein released by cells that has a specific effect on the interactions between cells, on communications between cells or on the behaviour of cells. The cytokines includes the interleukins, lymphokines and cell signal molecules, such as tumor necrosis factor and the interferons, which trigger inflammation and respond to infections.
On the basis of function, cell of secretion, or target of action, cytokines can be classified as lymphokines, interleukins and chemokines. The term interleukin was earlier used for cytokines whose targets were principally leukocytes. Majority of the interleukins are produced by T-helper cells. The term chemokine refers to cytokines that mediates chemo-attraction (chemotaxis) between cells.
Term Paper # 2.
Process and Classification of Cytokines:
Cytokines are released by cells into the circulation or directly into tissue. The cytokines locate target immune cells and interact with receptors on the target immune cells by binding to them. The interaction triggers or stimulates specific responses by the target cells.
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Classification of Cytokines:
The cytokines can be classified on the basis of structure and function.
On the basis of structure cytokines can be classified into the following types:
i. The four-α-helix bundle family — Cytokines of this family have three-dimensional structures with four bundles of α-helices.
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This family further includes three sub-families:
1. IL-2 subfamily
2. Interferon (IFN) subfamily
3. IL-10 subfamily.
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ii. The IL-1 family which includes IL-1 and IL-18
iii. The IL-17 families which have a specific effect in promoting proliferation of T-cells that cause cytotoxic effects.
Functional classification divides cytokines into those that enhance cellular immune responses, type 1 (IFN-g, TGF-β, etc.), and type 2 (IL-4, IL-10, IL-13, etc.)
Term Paper # 3.
Properties of Cytokines:
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A cytokine may exert:
i. Autocrine action by binding to the receptors on the membrane of the same cell that secreted it.
ii. Paracrine action by binding to receptors on the target cell in close proximity to the cell that secreted it.
iii. Endocrine action by binding to the target cells in distant parts of the body.
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Cytokines also exhibit various attributes like pleiotropy, redundancy, synergy, antagonism, and cascade induction. All these attributes permit the cytokines to regulate cellular activity in a coordinated and interactive way.
i. Pleiotropy:
When a given cytokine has different biological effects on different target cells, it is said to have pleiotropic action.
ii. Redundancy:
When two or more cytokines mediate similar functions, they are said to be redundant.
iii. Synergy:
When the combined effect of two cytokines on cellular activity is greater than the additive effects of the individual cytokines.
iv. Antagonism:
When the effects of one cytokine inhibit the effects of another cytokine.
v. Cascade Induction:
When the action of one cytokine on a target cell induces that cell to produce one or more other cytokines, which in turn induce other target cells to produce other cytokines.
Term Paper # 4. Detection of Cytokines:
Cytokines can be measured by analytical techniques, i.e., immunoassays and bioassays. However, high performance liquid chromatography (HPLC) and electrophoresis has also been used for the measurement of cytokine.
These techniques are used to measure:
(i) Intracellular cytokine levels.
(ii) Cytokine levels in the biological fluids.
(iii) Cytokine production by blood cells.
(iv) Cytokine receptors.
Bioassays:
Bioassays are slow and difficult to perform and therefore, bioassays are now being replaced by immunoassays. Thus, immunoassay is the practical method of choice for cytokine measurement.
A number of factors affect the measurement of cytokine levels. For example, cytokine inhibitors (auto-antibodies and soluble receptors) can bind cytokines and may contribute to inaccurate results. Collection tubes can become contaminated with microorganisms which act as a stimulus for the cytokine production. Cytokines can bind to receptors during their storage period. Cytokines can also be degraded during the storage period.
For Bioassays, pyrogen free tubes should be used for serum collection. Serum should then be stored at -80°C after centrifugation. Detection limit for bioassays is < 1 pg/mL. Bioassays have narrow assay range and less specificity. Assay time is 1-4 days. Calibration of bioassays is difficult.
Bioassays include the following approaches:
i. Cytotoxicity test.
ii. Proliferation tests.
iii. Test for chemotactic activity.
Advantages of Bioassays:
1. Sensitive (0.1 pg/mL).
2. Biologically active molecules can be measured.
Disadvantages of Bioassays:
1. Long analysis time.
2. Low precision.
3. Less specificity.
Immunoassays:
Specific antibodies can be generated against recombinant cytokines (as cytokines are proteins). Endotoxin is the major contaminant in the tubes containing heparin and cytokines can be released during coagulation. Therefore, for immunoassays of cytokines in biological fluids, protease inhibitors-plasma or EDTA-plasma is the suitable sample. Detection limit for immunoassays is 1-10 pg/mL. Immunoassays have wider assay range and are highly specific. Assay time is a few hours. Calibration of immunoassays is comparatively easier than bioassays.
Immunoassays include:
i. ELISA (Enzyme linked immunosorbent assay)
ii. IRMA (Immuno radiometric assay)
Disadvantages of Immunoassays:
1. Measure both, functional and non-functional cytokine levels.
2. Cross reactivity.
3. Detection limit.
Advantages of Immunoassays:
1. Excellent analytical performance.
2. Can be automated.
Cytokine scan also be measure by following techniques:
1. Immuno-histochemistry.
2. Flow cytometry.
Flow cytometry is the recent approach. It can identify and quantify the intracellular levels of cytokines in less than 2 hours. Flow cytometry analyses a large number of samples and gives results very rapidly. For flow cytometry, peripheral blood mononuclear cells are used. For more specific analysis, cells from synovial fluid, cerebrospinal fluid, broncho-alveolar fluid are also used.
Term Paper # 5
. Cytokine Receptors:
Structurally, all the receptors for various cytokines are quite diverse, but all belong to one of five families of receptor proteins mentioned below:
i. Immunoglobulin Superfamily Receptors:
Immunoglobulin superfamily receptors members of this family share structural homology with immunoglobulins, cell adhesion molecules, and some cytokines.
Examples- IL-1 receptor types.
ii. Class I Cytokine Receptor Family:
Class I cytokine receptor family (hematopoietin receptor family)—members of this family have some conserved motifs in their extracellular amino-acid domain.
Example- IL-2 receptor, whose g-chain deficiency is directly responsible for the x-linked form of Severe Combined Immunodeficiency (X-SCID).
iii. Class II Cytokine Receptor Family:
Class II cytokine receptor family (interferon receptor family)—members of this family are receptors for IFN β and g.
iv. TNF Receptor Family:
TNF receptor family members of this family share a cysteine-rich common extracellular binding domain and include several other non-cytokine ligands like CD40, CD27 and CD30, besides the ligands on which the family is named (TNF).
v. Chemokine Receptor Family:
Chemokine receptor family it is a seven trans-membrane helix family. Examples, all the G protein-coupled receptors belong to this family; two chemokine receptors (CXCR4 and CCR5), which act as binding proteins for HIV.
Term Paper # 6. Clinical Application of Cytokines:
Measurement of cytokine levels has gained interest in the last few years because of the following clinical applications:
1. Increased production of cytokines leads to elevated levels of cytokines in the body fluids (e.g., synovial fluid, amniotic fluid, blood, cerebrospinal fluid, broncho-alveolar fluid). Thus, cytokines can be directly implicated in the patho-physiological conditions.
2. Cytokine inhibitors (IL-IRA) and anti-inflammatory cytokines (IL-10, IL-13) are being used nowadays for treatment purposes. We need to monitor the level of cytokines during the course of such treatments.
3. Alterations in the normal cytokine levels indicate the occurrence of some diseases. For example, immune disorders and infectious diseases like (bacterial septic shock, bacterial toxic shock, rheumatoid arthritis, asthma, etc.).