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BIO407: Immunology

Unit 4: Antigen Presentation   *The immune system can combat individual threats, but in order to do so, it must be able to identify these threats.  Immunogenicity, that is, whether a compound causes an immune response or not, is related to how foreign the compound is, as well as its molecular weight, complexity, chemical composition, and physical form. In general, the more foreign, the more immunogenic a compound is. Compounds of larger molecular weight are more immunogenic. Because complexity increases immunogenicity, homopolymers are unlikely to be immunogenic. In terms of composition, proteins are more immunogenic than carbohydrates while lipids and nucleic acids are rarely immunogenic. In terms of physical form, particulates are more immunogenic than soluble compounds while denatured compounds are more immunogenic than native structures. Immunogenicity is also influenced by how much of a compound enters the body and the manner in which it enters.

B cells can recognize soluble antigens, but T cells only react to antigens presented to them. Antigen presentation is the process through which immune system cells (such as dendritic cells, B cells and macrophages) identify antigens and “present” them to T cells in a form that T cells can recognize.  Once antigens have been presented, the T cells can begin to eliminate these invaders from the body.  This unit will cover how antigens are recognized by immune-system cells and presented to T cells.*

Unit 4 Time Advisory
This unit will take you 6 hours to complete.

☐    Introduction to Unit 4

☐    Subunit 4.1: 0.75 hours

☐    Subunit 4.2: 1.25 hours

☐    Subunit 4.3: 1.5 hours

☐    Subunit 4.4: 1.25 hours

☐    Subunit 4.5: 0.5 hours

☐    Unit 4 Assessment: 0.75 hours

Unit4 Learning Outcomes
Upon successful completion of this unit, students will be able to:

  • List and describe the different factors involved in immunogenicity, and use this information to identify levels of immunogenicity associated with different molecules.
  • Identify and distinguish between the molecules and cells involved in B and T-cell recognition.
  • Answer questions, in some detail, about the pathways of antigen presentation of MHC I and II.

  • Lecture: The University of South Carolina School of Medicine: Dr. Jennifer Nyland’s “Antigens” Link:  The University of South Carolina School of Medicine: Dr. Jennifer Nyland’s “Antigens” (Adobe Flash, MP3 or Quicktime)
     
    Instructions: Click on the arrow of the Immunology folder to open it, then click on the “Antigens” lecture.  You have the choice of watching this on your computer with audio and slideshow or downloading the lectures to an MP3 player.  This will cover the material in Unit 4.
     
    This resource will take approximately 45 minutes to complete.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

4.1 Immunogenicity   4.2 Antigen Recognition by B and T Cells   4.2.1 Recognition by Immunoglobulins (Antibodies)   Note: An epitope is the portion of the immunogen that binds with the antibody molecule, the part that fits in the paratope of the antibody. Conformation is often found to be important in the recognition of an epitope by an antibody molecule because an antibody can react to soluble, unprocessed antigens. 

  • Reading: National Institutes of Health: Professor Charles Janeway et al.’s Immunobiology: “Antigen Recognition by B-Cell and T-Cell Receptors” Link: National Institutes of Health: Professor Charles Janeway et al.’s Immunobiology: “Antigen Recognition by B-Cell and T-Cell Receptors” (HTML)
     
    Instructions: Read this page in its entirety.
     
    This resource will take approximately 15 minutes to complete.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

4.2.2 Recognition by T Cells   Note: T cells recognize antigens as peptides presented in the major histocompatibility molecules on the surface of an antigen-presenting cell. These molecules were termed major histocompatibility for their discovery during transplantation reactions, so the name comes from the major role of these molecules in tissue (histo) compatibility. CD8+ T cells (cytotoxic T cells) recognize antigens presented by antigen presenting cells in MHC Class I molecules, and CD4+ T cells (helper T cells) recognize antigens presented in MHC Class II molecules.  The CD4 molecule binds to the MHC Class II molecule and the CD8 molecule binds to the MHC Class I molecule. These are required co-receptors of the interaction. MHC Class I molecules are on all nucleated cells in our body, whereas MHC Class II molecules are on antigen-presenting cells. Because of the requirement for antigen-presenting cell presentation, T cells recognize processed antigens.
 
The T cell receptors of most T cells are composed of an alpha chain and a beta chain. A small set of T cells have T cell receptors that have gamma delta chains. Unlike immunoglobulin, the B cell receptor, T cell receptors are not secreted. 

  • Reading: National Institutes of Health: Professor Charles Janeway et al.’s Immunobiology: “Antigen Recognition by T Cells” Link: National Institutes of Health: Professor Charles Janeway et al.’s Immunobiology: “Antigen Recognition by T Cells” (HTML)
     
    Instructions: Read from the beginning of this page through section 3-13 along with all associated figures.  This will cover the material in 4.2.2.
     
    This resource will take approximately 1 hour to complete.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

4.2.2.1 TCR? and TCR? (T-cell Receptor)   Note: This subunit is covered by the reading for subunit 4.2.2.

4.2.2.2 CD4 and MHC II   Note: This subunit is covered by the reading for subunit 4.2.2.

4.2.2.3 CD8 and MHC I   Note: This subunit is covered by the reading for subunit 4.2.2.

4.3 Recognition   - Reading: National Institutes of Health: Professor Charles Janeway et al.’s Immunobiology: “The Generation of T-Cell Receptor Ligands” Link: National Institutes of Health: Professor Charles Janeway et al.’s Immunobiology: “The Generation of T-Cell Receptor Ligands” (HTML)
 
Instructions: Read the introduction and section 5-1 along with all associated figures.  This will cover the material in 4.3.
 
This resource will take approximatley 1 hour to complete.

 Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.
  • Lecture: The University of South Carolina School of Medicine: Dr. Jennifer Nyland’s “Cells of the Immune System and Antigen Recognition” Link: The University of South Carolina School of Medicine: Dr.  Jennifer Nyland’s “Cells of the Immune System and Antigen Recognition” (Adobe Flash, MP3 or Quicktime)
     
    Instructions: Click on the arrow of the Immunology folder to open it, then click on the “Cells of the Immune System” lecture.  You have the choice of watching this on your computer with audio and slideshow or downloading the lectures to an MP3 player.  This will cover the material in subunit 4.3.
     
    This resource will take approximately 30 minutes to complete.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

4.3.1 Dendritic Cell and MHC II   Note: This subunit is covered by the reading for subunit 4.3.

4.3.2 Macrophage Activation   Note: This subunit is covered by the reading for subunit 4.3.

4.3.3 T Lymphocyte Activation   Note: This subunit is covered by the reading for subunit 4.3.

4.4 Antigen Presentation of MHC I   - Reading: National Institutes of Health: Professor Charles Janeway et al.’s Immunobiology: “The Generation of T-Cell Receptor Ligands” Link: National Institutes of Health: Professor Charles Janeway et al.’s Immunobiology: “The Generation of T-Cell Receptor Ligands” (HTML)
 
Instructions: Read sections 5-2 through 5-4 along with all associated figures.  This will cover the material in subunit 4.4.
 
This resource will take approximately 30 minutes to complete. 

 Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.
  • Lecture: The University of South Carolina School of Medicine: Dr. Jennifer Nyland’s “Major Histocompatibility Complex and T-Cell Receptors” Link: The University of South Carolina School of Medicine: Dr.  Jennifer Nyland’s “Major Histocompatibility Complex and T-Cell Receptors” (Adobe Flash, MP3 or Quicktime)
     
    Instructions: Click on the arrow of the Immunology folder to open it, then click on the first “MHC” lecture.  You have the choice of watching this on your computer with audio and slideshow or downloading the lectures to an MP3 player.  This will cover the material in subunits 4.4-4.5. Please don't be confused by a slight mistake at time 5:27 when the speaker accidentally says that Clas I molecules bind to T helper cells, although she means that Class I molecules bind to cytotoxic T cells. Also listen to her second file with the same title but with II in the title. 

    This resource will take approximately 45 minutes to complete.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

    Note: It is important to keep in mind that recognition of non-self and not self is key to understanding immunity. Recognition controls how an MHC Class I or MHC Class II molecule is loaded with the peptides that will be presented to T cells. While Class I molecules present antigens on the surface of the infected cells (endogenous antigens), Class II molecules present antigens taken up by phagocytosis. The method that loads Class I molecules is critically different from the method which loads Class II molecules.  helps  

4.4.1 Ubiquitination and Proteasome Degradation   Note: This subunit is covered by the reading for subunit 4.4.

4.4.2 TAP (Transporter associated with Antigen Processing) Transport   Note: This subunit is covered by the reading for subunit 4.4.

4.4.3 Binding to MHC I   Note: This subunit is covered by the reading for subunit 4.4.

4.4.4 Vesicular Presentation   Note: This subunit is covered by the reading for subunit 4.4.

4.5 Antigen Presentation of MHC II   - Reading: National Institutes of Health: Professor Charles Janeway et al.’s Immunobiology: “The Generation of T-Cell Receptor Ligands” Link: National Institutes of Health: Professor Charles Janeway et al.’s Immunobiology: “The Generation of T-Cell Receptor Ligands” (HTML)
 
Instructions: Read sections 5-5 through 5-7 along with all associated figures.  This will cover the material in subunit 4.5.
 
This resource will take approximately 30 minutes to complete.

 Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.

4.5.1 MHC II Invariant Chain   Note: This subunit is covered by the reading for subunits 4.4 and 4.5. 

4.5.2 Acidified Endocytic Vesicles   Note: This subunit is covered by the reading for subunits 4.4 and 4.5. 

4.5.3 MHC II Loading   Note: This subunit is covered by the reading for subunits 4.4 and 4.5. 

Unit 4 Assessment   - Assessment: The Saylor Foundation's "BIO407 Unit 4 Quiz" Link: The Saylor Foundation's "BIO407 Unit 4 Quiz" (PDF)

 Instructions: Please take the quiz. When you have finished, check
your work against the "[BIO407 Unit 4 Quiz Answer
Key](http://www.saylor.org/site/wp-content/uploads/2012/11/BIO407-Unit-4-Quiz-Answer-Key-FINAL.pdf)."
(PDF)  

 The assessment should take approximately 45 minutes to complete.