Bacterial Defense System Flashcards
What are the features of the adaptive immune response?
Specificity, Memory, and Tolerance
Explain specificity
Immune cells recognize and react with individual molecules (antigens) via direct molecular interactions
Explain the memory feature of the adaptive immune response
The immune response to a specific molecule is faster and stronger upon subsequent exposure because the initial antigen exposure induced growth and division of antigen-reactive cells, resulting in multiple copies of antigen-reactive cells.
Explain the tolerance feature of the adaptive immune response
immune cells are not able to react with self antigen. Self-reactive clones are destroyed during development of the immune response.
What is an antigen?
An antigen is anything the immune system recognizes as foreign. Reacts with an epitope ( short group or sequence of 4-6 amino acids).
What are antibodies?
Protein complexes that play a central role in both the specific and nonspecific immune system.
-produced by B-cells
-recognize specific regions of molecules called epitopes (the very tips)
What are the two different ways an antibody can bind to an antigen?
-Linear Sequence Determinants: A sequence of amino acids
-conformational Determinants: a group of amino acids that are close together when the antigen is folded.
What are lymphocytes and what two forms do they come in?
-Lymphocytes are antigen-specific leukocytes
-T-cells that mature in the thymus
-B-cells that mature in the bone marrow
What are B-cells?
-B is for bone marrow
-responsible for antigen interactions, antibody production, and immune memory (reminds what microbe is dangerous)
-have immunoglobulin (Ig0 molecules that are copies of the type of antibody the B-cell will produce and are on the surface
What happens to the B-cell after it is exposed to antigens?
They are split into memory cells or plasma cells
-Memory cells are long lived and can remain in the cortex for years
-plasma cells are differentiated antibody producing cells that only live for a few days (located in the medulla of the lymph node)
What are T-cells?
-T-cells are produced in the thymus
What are T-cell receptors (TCRs)
All T-cells have antigen-specific T-cell receptors on their surface and interact specifically with antigen.
Note: The antigen is always presented in processed form to the TCR by another cell-the aptly named antigen presenting cell or APC
What are the two types of APCs
-The amateurs: infected cells that present internally made foreign proteins (react for survival)
-The professionals (immune cells): phagocytes cells (macrophages) that ingest foreign particles and present proteolyses components on cell membrane (do it on purpose)
What are the two types of T-cells
-CD4 positive T helper cells
-CD8 positive cytotoxic T-cells
What are cytotoxic T cells?
CD8 positive cytotoxic T cells (CTLs) kill antigen bearing cells directly through interaction between a cell surface antigen on the target cell and the TCR (look at slide 28 to see how it works)
What are the two types of Helper T cells?
-TH1 cells: are responsible for recruiting and activating nonspecific effector cells like phagocytes (T inflammatory cells/ signals body to respond to antigen)
-TH2 cells: stimulate B lymphocytes to produce antibodies (signals to B-cells they have been infected w/antigens.
Where are T-cell receptors (TCRs) expressed and what do they consist of?
-TCR is expressed on the surface of all T cells -It consist of a constant region and a variable region that can bind specific antigens when they are presented on the surface of an MHC
-Like Igs, the variable region can recognize millions of different antigens
What are the two types of Major Histocompatibility Complex (MHC)
-Class I: which are on the surface of the amateur APCs (antigen presenting cells)
-Class II: on the. Surface of professional APCs like macrophages
NOTE: individual MHCs recognize a wide variety of antigens relative to Igs and TCRs
What happens between MHC class I APCs and Cytotoxic T cells
-Team up against intracellular pathogens and cancer cells-Class I MHCs present antigen that have been processed by the host degradation machinery and are bound by MHC class I in the ER
- MHC class I presenting antigen on the surface of a host cell interacts with TCR on the surface of cytotoxic T cells
What happens between MHC class II APCs and helper T cells?
-extracellular pathogens engulfed by phagocytes
-Class II MHCs bound to a self-peptide (li) line the inner surface of lysosomes of phagocytes cells (professional APCs)
-Foreign peptides formed from the degradation of the pathogen in the phagolysosome displace li and the complex is displaced to the surface of the APC
-MHC class IIs bound to antigen on the surface of the APC are recognized by T helper cells
What are Interleukins?
Cytokines that mediate interactions between leukocytes (how leukocytes talk to each other/ communication between white blood cells)
What is Interleukin 1 (IL-1) do?
-secreted by macrophages
-signals TH cells to make more TH cells
What is IL-2
-Produced by activated TH cell in response to IL-1(the signal)
-Binds to IL-2R on surface of TH cell
-Induces cell to divide and make clonal copies
What is IL-4?
-Produced by activated TH cells in response to IL-1 and IL-2
-Binds to IL-4R on B-cells
-Stimulates B cells to proliferate and differentiate into antibody producing plasma cells
What is Precise Definition (Cell mediated Immunity)
Any immune response that involves antigen-specific cells of the immune system but where antibody production or activity is not important
What is Working definition (cell mediated immunity)
Cell mediated immunity can only be transferred between animals by transferring lymphocytes
What is primary Response?
TH2 cell activated by APC presenting MHC II activated B-cell with same MHC II antigen complex on its surface
What is direct B-cell Stimulation?
In second encounter with antigen, antigen binding to antibodies on B-cell surface activate B-cell directly. This response is much more rapid.
What is the antibody primary response?
Following antigen introduction there is a latent period before a specific antibody appears in the blood. This is followed by a gradual increase in antibody titer and then a slow fall.
What is the antibody secondary response?
When a second exposure to antigen occurs several days or weeks later the antibody titer rises rapidly to 10 to 100 times that of the primary response.
