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97 Cards in this Set
- Front
- Back
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What happens to the "old" MHC proteins when a cell is infected by a virus? What is this called?
(2) |
The "old" MHC proteins exhibitng its own self-peptide will be degraded and replaced with a "new" MHC protein exhibiting the viral self-peptide protein. This process is called "turn over of proteins" and it occurs only in eukaryotic cells.
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How are MHC proteins I expressed on the surface of cells?
(2) |
MHC molecules must bind to antigenic peptides.
MHC class I proteins must bind to the antigenic peptides before it leaves the ER. MHC class I proteins are expressed on the surfaces of ALL nucleated cells |
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How are MHC proteins II expressed on the surface of cells?
(2) |
MHC molecules must bind to antigenic peptides.
For MHC class II proteins, the vesicle containing MHC class II proteins fuses with the vesicles containing antigenic peptides MHC class II proteins expression are more limited to certain cells. the MHC class II proteins can only be expressed on the "Antigen-presenting cells" (APC) such as macrophages, dendritic cells and B cells |
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Describe the structure of MHC class I proteins.
(3) |
MHC molecules consist of two types of polypeptide chains.
In MHC class I molecules, they have an α-chain transmembrane protein that that is non-covalently bound to a β2-microglobulin. Association of MHC I protein with β2-microglobulin is required for the expression of MHC I protein on the cell surface. MHC I has its groove within the α chains 3 types: HLA-A, HLA-B, HLA-C |
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Describe the structure of MHC class II proteins
(2) |
MHC II proteins are composed of 2 non-identical transmembrane polypeptides called α- and β- microglobulins
MHC II has its groove between the α and β chains 3 types: HLA-DP, HLA-DP, HLA-DQ |
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What is the function of MHC molecules?
(2) |
The goal of MHC molecules is to bind and present antigenic peptides derived from any protein types. This is so that it can activate an immune response to it.
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Why is polymorphism of MHC genes important in survival for any species?
(1) |
Polymorphism of MHC (presence of different alleles) is important to survival of any pathogen so that it is able to present and generate various immune response to various pathogen.
A reduction in MHC polymorphism may predispose species to infectious diseases |
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What are some cells that considered "Professional" antigenic-presenting-cells?
(2) |
dendritic cells, macrophages, and B cells.
These cells express primarily MHC class II proteins but may also express MHC class I protein |
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What are some similarities between both types of MHC proteins?
(4) |
1. MHC molecules must bind to antigenic peptides.
2. MHC molecules consist of two types of polypeptide chains. 3. each MHC class produces 3 types of proteins 4. Professional APC can express both classes of MHC proteins. 5. MHC genes are co-dominantly expressed. |
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Function of β2-microglobulin
(1) |
Association of MHC I protein with β2-microglobulin is required for the expression of MHC I protein on the cell surface.
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What are Antigens?
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plasma proteins that are recognized and bind to the immunoglobulins receptors of B cells and T cells receptors when complexed with MHC.
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What is common between B cells and T cells?
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1. have the ability to recognize AB when complexed with MHC.
2. they do not recognize the entire molecules of the Antigen. They only recognize a distinct part of the antigen known as epitopes or antigenic determinants. 3. Since only peptides can bind to antigens, the receptors of both cells can only bind to peptide antigens. |
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Describe the properties of the immunoglobulin B cell receptor.
(2) |
1. they only recognize the epitotes that are intact to naive, unprocesses Antigen
2. They can recognize several types of antigens: lipids, carbohydrates, chemicals and proteins |
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Describe the properties of the immunoglobulin T cell receptor.
(2) |
1. It can only recognize peptides or processed antigens that are complexed with MHC molecules attached to the surface of APC molecules.
2. 2 types of APC that usually activates a T cell is primarily dendritic cells but can also be activated by macrophages. |
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How are lymphocytes processed during the developing stages?
(1) |
In their developing stages, immature lymphocytes undergoes screening where if the lymphocytes are unresponsive towards self-antigens then they would be eliminated.
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What does "antigen processing and presentation" refer to?
(1) |
it refers to the degradation of the protein into peptide fragments (processing) and the binding and display of the Ag as a peptide fragment when bound to MHC mlcs on the surface of cell (presentation)
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What are the 2 systems for processing and presenting protein in peptide fragments?
(2) |
1) the first system deals with proteins that are intracellular created.
2) the second system deals with proteins that are taken up via phagocytosis or endocytosis, |
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Describe the first processing-and-presenting-protein system. Talk about the process, as well.
(5) |
1. It involves normal, intracellular, proteins in healthy, uninfected cells
2. It also involves viral proteins from viral-infected cells 3. Proteins are synthesized via the free ribosomes in the cytoplasm of the uninfected cells. 4. Peptides-MHC complex presented to T cells 5.[process] the protein is degraded into peptide fragments by protease-complex known as "PROTEASOME". A specific transporter called TAP transport the peptides from the cytoplasm into the lumen of ER, where peptides are complexed with MHC class I protein molecules. MHC class I proteins are then transported to the surface of the cell where it will be presented into the T cells. |
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Describe the second processing-and-presenting-protein system. Talk about the process, as well.
(2) |
1. Involves normal extracellular proteins (blood proteins), virus, bacteria and toxins.
2. Only specialized APC cells can present antigens from these sources. APC express primarily MHC class II proteins. 3. [process] a) Soluble proteins (blood proteins, toxins) are taken up by cell via endocytosis into an intracellular vesicle where they will be degraded into peptides. b) Bacteria and viruses are taken in by cell via phagocytosis into an intracellular phagosome vesicle , which fuses with the lysosome vesicles containing protease, lysozyme and other bactericidal substances, PROTEASE degrades the bacterial and viral proteins into peptides. These peptides remain inside the vesicles and are NOT IN THE CELL's cytoplasm. c. for all the proteins involved, MHC class II proteins leave the ER in a vesicle and fuses with the organelle processing the antigens (endosome, phagolysosome) and binds the peptides. MHC class II protein complex is then finally transported to cell surface where it will be presented to T cells. 4. Toxins, blood proteins, bacteria and virus-derived peptide antigen complex with MHC class II proteins are expressed on the cell surfaces of macrophages, dendritic cells and B CELLS. |
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What is a TCR?
(3) |
a membrane bound protein receptor composed of 3 parts:
1. an Ag-binding receptor that is composed of both TCR-α and TCR-β polypeptides. 2. a signaling subunit, CD3 complex 3. CD4 or CD8 accessory molecule (never both) |
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TCR components:
a. TCR-α and TCR-β are polypeptides joined together by a disulphide bond |
1. they are diverse. It involves the rearrangement of TCR "gene segment" to form a complete gene.
2. they are expressed at cell surface 3. Each polypeptide has one (V) Variable and (C) constant region. Vα and Vβ combine to form an Ag binding site. There is only one Ag binding site in each TCR. 4. Function of the Antigen binding portion: i. to recognize Ag-peptides that are bound to MHC proteins ii. they do not recognize native, unprocessed intact Antigen. 4. |
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TCR components:
b. CD3 of TCR (what is its function?) (2) |
The 2 functions of CD3 of the TCR:
1. It sends signals to the nucleus of the T cell to divide when T cells bind to the antigen-peptide MHC protein of the APC 2. It activates the T cell and causes it to divide |
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TCR components:
c. co-receptors CD4 and CD8 (3) |
1. they are effector molecules
2. they have 2 functions: a) they bind to the Antigen-peptides on the MHC class I proteins and be bound to different sites of TCR. b) this binding increases the affinity of interaction between T cell (TCR) and APC (MHC peptide complex) c) they do not influence the antigen specificity of the TCR. ----- CD4 + TCR = Helper T cells ----- CD8 + TCR = Cytotoxic T cells (TLC) |
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What do the developing T cells experience during maturation?
(4) |
*****DURING T CELL DEVELOPMENT IN THYMUS, THYMOCYTES START TO EXPRESS THE TCR AND both CD4 AND CD8 CO-RECEPTORS.
2 types of screening process: 1. Positive selection (immediate process) 2. Negative selection 3. Tregulation |
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T Cell Maturation:
1. Positive selection Describe the functions (2) and it's process (2) |
Function:
- ensures that the thymocyte will be reactive against MHC protein displaying foreign antigenic peptides. - this is to guarantee effective immunity against pathogens [process] 1. only thymocytes that have a TCR capable of binding to MHC I & 2 are positively selected by thymic epithelial cells. 2. those positively selected will receive a "survival signal" and permitted to mature. Those without this signal dies of neglect. 3. ULTIMATELY AT THE END, those positively selected are based on their TCR low affinity binding to the MHC class 1 & 2 proteins. |
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T Cell Maturation:
2. Immediate process between Positive and Negative selection (1) |
After positive selection, the thymocytes stop expressing both accessory molecules and only begin expressing EITHER CD4 ORCD8.
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T Cell Maturation:
3. Negative selection Describe the functions (3) and its process (4) |
Function:
1. to ensure that the mature T cells are not self-reactive 2. Ensures that the mature T cells are TOLERANT against self-antigens. Process: 1. is subjected to screening process by dendritic cells and macrophages 2. Those that bind to the Ag-peptide MHC class 1 or 2 proteins with high affinitty are directed to be "apoptosis" (process of elimination) 3. Only those with low affinity towards MHC-self antigen peptide are permitted to mature into functional T cells and leave the thymus. ** this process is not limited to self-antigen expressed in the thymus! "Autoimmune regulator (AIRE)" is regulatory gene expressed in THYMIC epithelial cells that promotes a wide variety of tissue Ag. |
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T Cell Maturation:
4. Negative Selection Escapees: T-regulation Function (3) |
refers to those T cells that are self reaction but was unfortunately enough to bypass the Negative selection.
1. regulates the activity of self-reactive T cells 2. produces T-regulatory (T-reg) cells that is thought to be dependent on relatively high affinity interactions with self-Ag |
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What is the Antigen binding site on the TCR complex comprise of?
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the Vα and Vβ portion of the polypeptides TCRα and TCRβ.
There is only 1 Antigen binding site for each TCR complex molecule. |
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this TCR developing screening process is not limited to self-antigen expressed in the thymus!
What is AIRE? (1) |
this process is not limited to self-antigen expressed in the thymus! "Autoimmune regulator (AIRE)" is regulatory gene expressed in THYMIC epithelial cells that promotes a wide variety of tissue Ag.
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What is a T-regulatory cell?
(4) |
1. It is a T cell generated in they thymus that regulates the activity of self-reactive T cells.
2. It expresses a high level of CD25 (a part of the IL-2) 3. It prevents conventional T cells from mounting immune response. 4. There are different types of T regulatory cells outside the thymus and are not necessarily specific for self-Ag. |
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What is the function of the Antigen-binding site on the TCR molecule?
(2) |
Function of the Antigen binding portion:
i. to recognize Ag-peptides that are bound to MHC proteins ii. they do not recognize native, unprocessed intact Antigen |
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What is clonal selection?
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the activation process of mature T cells who are capable of binding to APC's MHC Antigen-peptide.
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After TCR binds to the MHC peptide complex on the APC, CD3 of TCR signals TCR to activate and divide.
How does the differentiation work? What is the difference between H1 T cell and H2 T cell? |
T cells are differentiate into T helper 1 cells and T helper 2 cells based on which accessory molecules is associated with it.
T h1 cell = TCR + CD4 - function: recognize antigenic peptides/ epitopes that are only found in MHC II proteins on APC T h2 cells: - function: recognize antigenic peptides/ epitopes found on MHC class I proteins on APC. |
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Recap:
How is the T cell activated? What is difference found between non-APC and APC when activating cells? Why is APC unique? |
T cells are activated via 2 signals:
[signal 1] occurs during binding between the APC MHC-peptide and the TCR. CD3 mlc signals T cell to divide [signal 2] occurs during the interaction between B7 co-stimulatory mlc found on the APC and CD28 accessory molecule of TCR. The difference between non-APC and APC when activating cells is that non-APC are less efficient in providing signal 2. Example of non-APC is epithelial star. APC are unique in that they are they only ones that can activate the T cells since they are the only cells that contain the necessary co-stimulatory particles. (CD28 and CD3) |
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What is "clonal anergy"?
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Clonal anergy is a state of non-responsiveness a T cell will undergo if it only receives signal 1 and not signal 2.
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What are APC (3) and what are their functions as an APC (3)? How do each of them differ (1)?
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APC consist of dendritic cells, macrophages and B cells.
Function of APC: 1. provide stimulatory signal 2 to completely active T cell. 2. expresses B7, co-stimulatory molecule, which binds to the CD28 mlc on the APC in order to expess signal 2 The APC differs in their expression of B7 |
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Describe the Dendritic cells in their immature (3) and mature forms (4)
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[immature]
1. highly phagocytic 2. does not contain homing signal to LN or other peripheral organs. 3. found in tissues (in skin, they are known as "Langerhann Cells") [mature] 1. maturation occurs when it phagocytose its first pathogen and the PRRs interact with the pathogen's PAMPs. 2. express high concentration of [MHC class II] and [B7] 3. express homing receptors to LN and other peripheral signal 4. becomes powerful activators of T cell (but by then, they are no long phagocytic) |
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Describe macrophages cells in their immature (2) and mature forms (2).
How do the macrophages mature? |
[immature]
1. Express small [MHC class II] 2. Express no [B7]. therefore, unable to active naiive, T cells [mature] 1. increase expression in [MHC class II proteins] and [b7] 2.able to active T cell Maturation is stimulated by phagocytosis of an Ag and the interaction between PRRs and PAMPS. |
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How are macrophages infected by bacteria activated?
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Macrophages infected with bacteria are activated via Helper 1 T cells... allowing macrophages to eliminate bacteria more efficiently.
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Describe the B cells in their immature (2) and mature forms (3)
How are B cells activated? |
[immature]
1. expess low [MHC class II] 2. do not express [b7] [mature] 1. increase its expression of MHC class II and b7 2. if interaction between PRRs and PAMPs occur, B cells will upregulate their expression of B7 molecules. |
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How does Helper T cells differentiate into TCH1 and TCH2?
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Helper T cells differenttiate into TCH1 and TCH2 based on the cytokines environment they are exposed to. Generation of either TCH1 or TCH2 are cytokine mediated/dependent.
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How do Helper T cells become TCH1 and TCH2?
Macrophages and DC (APC) produces different cytokines during infection in which bacteria replicates outside the APC vs. an infection in which bacteria replicate inside APC |
Macrophages and DC (APC) produces different cytokines during infection in which bacteria replicates outside the APC vs. an infection in which bacteria replicate inside APC
Helper T cells exposed to a) IL-12 and IL-18 (produced by macrophages or DC): become TCH1 * cytokines produced by macrophages or Dc positive regulates the APC that produces it and negatively regulates the other subsets. b) IL-4 (produced by mast cells): becomes TCH2 |
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What is the function of TCH1?
(4) |
1. involved in many cytokine-mediated/dependent activities. For e.g. in the activation of macrophages where TCH1 generates a positve feedback by activating the macrophages in return. this helps macrophages to kill bacteria more efficiently.
2. involved in delayed-type sensitivity reactions 3. involved in activation of cytotoxic cells. 4. the cytokines produced by one subsets of the T helper cells positive regulates the subset that produces it and negatively regulates the other subsets |
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What is the function of TCH2?
(1) |
helps B cells produce antibodies
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Relate the activation of macrophages to the T H1 cells.
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the cytokines (IL-12, IL-18) produced by one subsets of the T helper cells (TCH1) positive regulates the subset (TCH1) that produces it (IL-12, IL 18) and negatively regulates the other subsets
In other words, macrophages and dendritic positively regulates itself?????????? |
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Activation of CTL-Precursor into a functional CTL requires?
(3) |
Cytotoxic t cells required 3 steps:
1. [signal 1] TCR binding with Ag-peptide MHC I on APC triggers CD3 to signal nucleus to differenctiate 2. [signal 2] B7 co-stimulatory molecule of APC interaction with CD28 of TCR 3. Sufficient concentration of IL-2 is needed to drive its differentiation -- majortity of IL-2 is provided by activated CD4 T cells (helper 1), some are made by CD8 T cells. |
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What is the function of activated CD8 T cells (cytotoxic T cells)?
(4) |
1. kills target cells by releasing perforin to lyze infected cell
2. release granzyme to induce apoptosis (programmed cell death) 3. important in eliminating viral and tumor based cells 4. they are involved the rejection of transplanted tissues. |
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how does the binding of the TCR (cytotoxic T cell) to MHC class I proteins help the binding of CD8 with the MHC proteins?
(1) |
Recognition of the TCR of the cytotoxic cell with the viral-Ag peptide on MHC I proteins enchances the binding of CD8 of cytotoxic T cell with the MHC proteins.
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what is the difference between an inactivated naiive cytotoxic cell and a mature one?
(1) |
A mature cytotoxic cell can recognize Antigen present in the MHC class I proteins and eliminate the pathogen.... but the naiive cytotoxic cell (precursor) are incapable of killing target cells yet.
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what happens when CD8 T cells becomes activated?
(1) |
they turn in to killer cytotoxic cells.
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Where is do the B cells mature and reside in?
(1) |
bone marrow
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What is a B cell?
(3) |
1. It is a modular receptor
2. It's immature form undergoes a screenning process called "clonal delection" where if it's mIg bind to an Antigen (usually self) in the bone marrow, the Ig-α and Ig-β co stimulatory molecules will send signals to cause the cell to die. 2. For those with unbound mIg are permitted to mature and leave the bone marrow, circulate in blood and reside in the spleen and lymph node. 3. the b cell is composed of 2 units: a) membrane bound immunoglobulin (mIg) b) Ig-α and Ig-β co-stimulatory molecules. |
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BCR subunits:
1. membrane bound immunoglobulin (mIg) (3) |
1. the mIg component of the mature, naiive B cell can differentiate into either IgM or IgD.
2. Each Ig molecule consist of 4 polypeptides: 2 identical heave and light chains. Each chain has one Variable and one Constant region. The V heavy and V light join together to form an antigen binding pocket. Since there are 2 of each region, there is 2 Antigen binding sites per immunoglobulin. 3. All mIg on the same B cell have the same Ag specificity becuase they all have the same V light and V heavy regions. Hence a single B cell can only bind to 1 or few similar epitopes. |
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BCR subunits:
2. Ig-α and Ig-β (1) |
the function of Ig-α and Ig-β
1. co-stimulatory molecules that send termination signal that cause the immature B cells to die if the mIg of the immature B cell binds to Ag in the bone marrow. (clonal deletion) |
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What is clonal deletion?
(1) |
A screening process that terminates immature B cells whose mIg binds to the Ag (usually self) in the bone marrow. Termination is signaled by Ig-α and Ig-β
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What is the relationship between activated T helper 2 cell and activating B cell?
(1) |
When B cells receives additional signals from activated helper T cells, it will proliferate. Some progeny will differentiate into AB-secreting plasma cells or into memory B cells.
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How do B cells activate? (turn into AB secreting plasma cells or memory B cells)
(3) |
Activation requires 2 signals.
[signal 1] occurs when Antigen cross-link with mIg (when 1 Antigen is bound by several mIg of B cell). This results in the internalization of Antigen and an increase expression of MHC class II and B7 molecule so that B cells can act as an APC for T cells. [Signal 2] When T cell is activated with its 2 required signals, it also begins to express CD40L (ligand). The 2nd signal is mediated by the binding of CD40 on b cell with CD40L on the activated T (h2) cell. 3. In addition, T (h2) must provide B cells with cytokines to complete B cell activation. |
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How can B cell get activated without T cell
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Some antigens (such as LPS or polymeric antigens) can activate B cellls in the absences of T cell because the cross-linking of mIg by these antigen are sufficient to activate B cells to convert adn secrete mIg into IgM. These are sometimes refered to as mitogens. This mitogenic response is less sophisticated and do not generate memory B cells.
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when B cells binds an Antigen by its mIg, it brings the Ag inside the cell by receptor-mediated endocytosis (PRRs)
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when B cells binds an Antigen by its mIg, it brings the Ag inside the cell by receptor-mediated endocytosis (PRRs)
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What is an antibody (AB)?
(3) |
a plasma secreting B cell that is also considered as an immunoglobulin.
- It circulates in blood and other fluid. - It provides humoral immunity: an fluid immunity that is due to antibodies. |
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What are the functions of an Antibody?
(6) |
1. provide humoral immunity
2. binds to foreign macromolecules 3. prevent virus and toxins from entering cells. 4. binds to Ag's epitope 3D structure via complementary Key-fit-lock interaction 5. targets Ag for phagocytosis by neutrophils and macrophages. 6. Promotes opsonization by allowing more types of bacteria to be eliminated efficiently via Complementary proteins. |
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Describe the structure of the antibody.
(9) |
1. 4 polypeptides: 2 Light and Heavy chains (1 variable and 1 constant)
2. Light chains consist of 2 types: kappa (κ) and lambda (λ) 3. 5 types of heavy chain: α (alpha), μ (mu), ε (epsilon), γ (gamma), δ (delta) 4. The type of Heavy chains defines the class of Ig class (aka isotypes): IgG (γ), IgM (μ), IgA (α), IgE (ε), IgD (δ) 5. Each isotope can have either κ or λL chains but never both. 6. The N-terminal portions of both H and L chains are the variable regions (V light and V heavy) and may vary from one AB to another, 7. The rest of the Heavy and Light chains are Constant region and are identical for all chains. 8. The Hypervariable (HV) regions within the Variable regions consist of 3 a.a. that vary from one AB to another that make up the AB-binding site. The a.a in here determine the shape of the side chains of the HV region and binds to the AB with high affinity. 9. The 4 polypeptides are held via S-S bonds which forms when 2 cysteine residues whose R groups (CH2-SH) becomes covalently linked to form CH2-S-S-CH2 bond. |
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why is the difference of a.a in the C regions of heavy chains important?
(2) |
It causes problems during tissue transplantation.
However it is possible for another species (e.g goat) to generate an AB that recognizes the heavy chain C region of the human AB. These antibodies are called species (goat) anti-human Ig because it is a goat antibody that recognizes the constant region of a human antibody. |
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What is the functions of the heavy chains (αμεγδ) in the C regions? What of the light chains in the C regions (κλ)
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The function vary based on the various amino acid sequences in its C region. These a.a sequence determines the function of the antibody and how it help eliminate the antigen.
The light chains in the C regions may have variable a.a but it does not influence the function of the antibody. |
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What are the key features of Antibodies?
(3) |
1. the Variable regions of the heavy and light chains determine the Ag-binding specificity of antibodies.
2. The H chains C region determine the function of the antibody 3. The H chain C region is species specific. It allows the possibilities of generating AB in one species that recognizes H chain of C regions of different species. |
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why is an Antibody referred to as bivalent?
(2) |
An antibody is bivalent because it has 2 identical antigen binding site (due to 2 heavy and 2 light chains).
Its shape is determined by the R-groups that make up the HV regions. The shape determines the specificity of Antibodies. |
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What is the difference and similarities between both IgM and IgD?
(3) |
IgM and IgD are capable of activating Complement proteins
Only IgD can bind to the receptor of phagocytic cells Only IgM can be produced without the help of T (h2) cells. |
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What does the binding of the AB to epitopes rely on?
(2) |
The ability of AB to bind to epitope depends on the surface shape complementary. Close contact allows formation of H-bonds as well as ionic and hydrophobic interactions between the epitope and the Ag bindign site.
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Describe the synthesis of AB.
(1) |
Synthesis of AB follows protein synthesis.
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Where can antibodies be found in body?
(2) |
B cells secrete AB into extracellular fluid, found mainly in blood. AB are also found in fluids such as breast milk, tears, saliva, gastrointestinal secretions, mucus (IgA)
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What are the main type secreted Antibodies?
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IgA, IgG and IgM
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What AB are secreted in individuals who has allergies?
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IgE
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Why can AB of different isotopes recognize the same antigen?
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Ab of different isotopes can recognize the same antigen because they have the same V region although their C regions are the same.
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Structure and Function of Secreted Antibodies:
1. IgM (5) |
[Structure]
1. pentamer structure with five IgM monomer bonded by disulphide bonds. 2. there is 2 IgM monomers that will be bonded via a Joining J-polypeptide chain. 3. Although the Antigen binding site has a low affinity, the IgM pentamer has a high avidity (total binding strength) because there will be a total of 10 binding sites. 4. It is a major class serum secreted in the primary adaptive immunity response. 5. Function: to kill bacteria by coating them with IgM so that complement proteins can lyse them. The a.a in μ chain of the constant region binds to the complement proteins. |
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Structure and Function of Secreted Antibodies:
2. IgG |
1. it is a major class serum in the secondary adaptive immune response (second time encounter)
2. It eliminated bacteria in 2 ways: a) C proteins kills bacteria coated with IgG. a.a sequence in the γ chain constant region bind to complementary proteins. b) Opsonization: Phagocytes ingest bacteria coated with IgG antibodies more readily. a.a sequence in the γ chain constant region bind to complementary proteins. 3. in pregnancy, AB is transfered from mother's placenta to provide protection for the fetus. |
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why is an Antibody referred to as bivalent?
(2) |
An antibody is bivalent because it has 2 identical antigen binding site (due to 2 heavy and 2 light chains).
Its shape is determined by the R-groups that make up the HV regions. The shape determines the specificity of Antibodies. |
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What is the difference and similarities between both IgM and IgD?
(3) |
IgM and IgD are capable of activating Complement proteins
Only IgD can bind to the receptor of phagocytic cells Only IgM can be produced without the help of T (h2) cells. |
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What does the binding of the AB to epitopes rely on?
(2) |
The ability of AB to bind to epitope depends on the surface shape complementary. Close contact allows formation of H-bonds as well as ionic and hydrophobic interactions between the epitope and the Ag bindign site.
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Describe the synthesis of AB.
(1) |
Synthesis of AB follows protein synthesis.
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Where can antibodies be found in body?
(2) |
B cells secrete AB into extracellular fluid, found mainly in blood. AB are also found in fluids such as breast milk, tears, saliva, gastrointestinal secretions, mucus (IgA)
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What are the main type secreted Antibodies?
(3) |
IgA, IgG and IgM
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What AB are secreted in individuals who has allergies?
(1) |
IgE
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Why can AB of different isotopes recognize the same antigen?
(1) |
Ab of different isotopes can recognize the same antigen because they have the same V region although their C regions are the same.
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Structure and Function of Secreted Antibodies:
1. IgM (5) (5) |
[Structure]
1. pentamer structure with five IgM monomer bonded by disulphide bonds. 2. there is 2 IgM monomers that will be bonded via a Joining J-polypeptide chain. 3. Although the Antigen binding site has a low affinity, the IgM pentamer has a high avidity (total binding strength) because there will be a total of 10 binding sites. 4. It is a major class serum secreted in the primary adaptive immunity response. 5. Function: to kill bacteria by coating them with IgM so that complement proteins can lyse them. The a.a in μ chain of the constant region binds to the complement proteins. |
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Structure and Function of Secreted Antibodies:
2. IgG (3) |
1. it is a major class serum in the secondary adaptive immune response (second time encounter)
2. It eliminated bacteria in 2 ways: a) C proteins kills bacteria coated with IgG. a.a sequence in the γ chain constant region bind to complementary proteins. b) Opsonization: Phagocytes ingest bacteria coated with IgG antibodies more readily. a.a sequence in the γ chain constant region bind to complementary proteins. 3. in pregnancy, AB is transfered from mother's placenta to provide protection for the fetus. |
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Structure and Function of Secreted Antibodies:
c. IgA (6) |
~ in serum, it exist as a monomer.
~ in body secretions, it exist as a dimer that are connected by a J-polypeptide chain. ~ it is associated with a "secretory piece" which aids in bringing IgA across layers of epithelial cells and get to various body sites. ~ it is a major class in external body secretion (e.g. tears, saliva, breast milk) ~ Function: it binds and neutralize pathogens, preventing the attachement of pathogens to host's surfaces. ~ IL-5 induces AB class switching to IgA |
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Structure and Function of Secreted Antibodies:
d. IgE (3) |
~ secreted in serum but MAJORITY of it binds to mast cells' and basophils' receptor (FRI). It is the only AB class that binds to this receptor.
~ It is responsible for triggering allergic response. IgE binds on mast cells' and basophils' binding to Ag... which causes cell to degranulate and release large concentration of histamine... which stimulates allergic responses. ~ it is also the primary AB class secreted during parasitic infections. Mast degranulation result in diarrhea and vomitting helps expel worms. |
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Whe is the adaptive immune response induced?
(1) |
Adaptive immune response is triggered when naiive, incompetent T or B cells encounter Antigen and becomes activated and proliferate until there is a population of cells with specificity against that antigen. During clonal selection and expansion, progeny cells differentiate into effector cells or memory cells.
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Describe the Primary response of the adaptive immune system.
(3) |
1. It is induced when it first encounter an antigen for the first time.
2. Response is not immediate; it takes up to 5-7 days after immunization with Antigen before Antibody can be detected. 3. During the delay period, a) mature, naive B cells with mIg (IgM or IgD) bind to its specific antigen and becomes activated. b) Signal from Helper T cells cause the activated B cell to divide and make identiacal daughter cells with same Antigen specificity. c) B cells divide into plasma secreting cells or memory B cells. |
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How is inducibility demonstrated in adaptive immunity?
(1) |
Activated b cells divide into plasma cells that secretes large amount of IgM. This demonstrates inducibility of the adaptive immune system as concentration of Antibodies increase in blood serum.
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Describe the Secondary response of the adaptive immune system.
(3) |
1. is induced when B cells is re-immunized with same Ag.
2. response is faster and more vigorous. 3.Memory T(h2)cells and B cells are reactivaed and BC respond quickly by differentiating into more memory cells and plasma cells (demonstrates memory of the AIS), The more plasma cells develop, the more AB is secreted. AB is typically IgG. |
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What are memory B cells?
(1) |
They are long lived cells that do not secrete AB and have the same Antigen specificity as the mIg on the original B cells
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How is specificity demonstrated in the AIS?
(1) |
It is demonstrated by immunizing with a second different Antigen. Immune system will develop a separate primary response to this new antigen.
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What does "immunoglobulin class switching" means?
(2) |
It means that activated helper T cell releases cytokines to induce B cells to switch to a particular class of AB.
In the 2ndary response, the plasma cells secrete AB that have the same Ag specificity as IgM (secreted in primary response) but the AB is not IgM; rather the AB is mostly IgG (some IgA and IgE). IgG has a different heavy chain in the constant region. |
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What does "active immunity" mean?
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It means the immune system produces effector cells (plasma cells producing AB, activate T cells) and memory cells.
2. It can be induced via a) naturally via exposure to pathogen b) artificially via vaccination |
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What does "passive immunity" mean?
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1. It is an immune system that provides immediate but temporary immunity.
2. It is the transfer of pre-formed AB or activated T cells from an immune donor to a non-immune recipient. 3. It can be acquired via a) naturally - important in the early life development before the child's adaptive immune system is fully developed. - IgG AB from mom crosses placenta to provide protection to fetus - IgA AB from breast milk provide immunity for baby before immune system is developed. b) artificially - in life threatening emergencies - when primary immunity is unable to make enough specific AB to neutralize virus or toxin. Therefore, passive immunity treatment allows for pathogen neutralization. |
