Session 9 - Immunity system 2 Flashcards
What are antigens
Antibody generators.
o Substances that are recognized as foreign and provoke immune responses are called antigens (Ags)
• Can be entire microbes, parts of microbes, bacterial toxins, pollen, transplanted organs, incompatible blood cells
(whole cells, parts of cells or chemicals)
Characteristics of antigens
- Immunogenicity = ability to provoke immune response
- Reactivity = ability to react to cells or antibodies it provoked
Describe the entrance of antigens and where they end up - why?
when they get past the bodies nonspecific defenses (physical and chemical barriers) antigens are directed to lymphatic tissues.
- enter the bloodstream to be deposited in spleen
- penetrate the skin and end up in lymph nodes
- penetrate mucous membranes and lodge in mucosa associated lymphoid tissue
** remember B cells and T cells are sitting there trying to detect antigens
Structure of Antigens/ Epitopes
o Structure: Large, complex molecules, usually proteins
o Epitope: small part of antigen that triggers/ creates the immune response
– antigenic determinant
Antigen Receptors
Where are they found and What casues diversity?
o Antigen Receptors: Present on plasma membranes of lymphocytes that can recognize and respond to a billion different epitopes - even artificially made molecules
o Diversity: Genetic recombination of few hundred small gene segments produce a huge variety of antigen receptors
o Specificity: Each B or T cell has its own unique set of gene segments that codes its unique antigen receptor in the cell membrane
Major Histocompatibility Complex Antigens - what are they and what are the two types ?
Self antigens, surface markers (flags that say ‘this is me !’)
o They define our cells as ‘self’
o They also serve as a signal to lymphocytes that antigens/ pathogens are present
- Glycoproteins located in the plasma membrane of all body cells
- Also called Human Leukocyte Antigens (HLA)
**o Two types:** • MHC class I antigens • MHC class II antigens
Major Histocompatibility Complex Antigens :
MHC-I antigens - where are they located and their function
built into the cell membrane of all cells except red blood cells
o Function: If a cell is infected with a virus, the MHC-I contains bits of virus marking the cell so T cells recognize that there is a problem in that cell
Major Histocompatibility Complex Antigens:
MHC-II antigens: where are they found and their function
Appear only on membrane of Antigen Presenting Cells (Dendritic cells, macrophages, B cells)
o Function: If antigen presenting cells ( Dendritic cells, macrophages, B cells) ingest foreign proteins, they will display some as part of their MHC-II
* this will tell innitate immune response!
Antigen recognition
B and T cells must recognize a foreign antigen before beginning their immune response
- B cells can bind to antigens in lymph, interstitial fluid, or blood plasma.
- T cellscan only recognize fragments of antigens that have been processed and presented to them as part of a MHC molecule
–Helper T cells “see” antigens if part of MHC-IImolecules on surface of antigen presenting cell
–Cytotoxic T cells “see” antigens if part of MHC-I molecules on surface of body cells
Processing of Exogenous Antigens
o Exogenous Antigens: Foreign antigens that are present in fluids outside body cells
•These include bacteria and bacterial toxins, parasitic worms, inhaled pollen and dust, and viruses that have not yet infected a body cell.
oProcessed by: Antigen-presenting cells (APCs) and presented together with MHC class II molecules to T cells to alert that “intruders are present”.
Refer to diagram ** when the MHC11 has something attached to it, this is an indication for B and T cells to start working
Processing of Endogenous Antigens
oEndogenous antigens: Foreign antigens that are present within the body cells
•include viral proteins or proteins produced by cancer cells
oProcessed by: Most of the body’s cells can process endogenous antigens
- Fragments of endogenous antigen are associated with MHC class I molecules inside the cell.
- The antigen-MHC-I complex moves to the cell’s surface where it alerts T cells
Interleukin 2 - Cytokine
Describe and what is their function
Small protein hormones secreted by lymphocytes and antigen presenting cells, fibroblasts, endothelial cells, monocytes, hepatocytes, and kidney cells
oFunctions:
ostimulate or inhibit many normal cell functions, such as cell growth and differentiation.
oAre essential in the immune responses of T and B cells through the process of ‘co-stimulation
A T Cell is activated when it recieves two signals - Explain
There are two types of T Cells.
•Helper T cells & Cytotoxic T cells
oFirst signal: Antigen recognition by a T-cell receptor (TCR)
•T-cell receptors (TCRs): recognize and bind to specific foreign antigen fragments that are presented in antigen–MHC complexes
oSecond signal: Costimulation by costimulators or plasma membrane molecules
•Costimulators: cytokines such as interleukin-2 (IL-2)
Activation of Helper T Cells
The helper T cell becomes activated through
- Antigen recognition: TCRs on Helper T cells bind to foreign antigen fragment associated with MHC-II at the surface of an APC with the help of CD4 proteins
- Costimulation: by interleukin-2
Clonal Selection of Helper T Cells
Clonal Selection: activated helper T cell undergoes clonal selection to form a clone of helper T cells:
- Active helper T cells: secrete cytokines including interleukin-2 (IL-2), ( Once they are activated the helper T cells actively divide so now we have clones of that exact same helper T cell which recognises that specific antigen that it was just bound to)
- Memory helper T cells: Available for swift response if a second exposure should occur ( Sit in your lymph nodes and recognise antigens that have infected before)
oInterleukin-2 (IL-2): act as a costimulator for resting helper T cells or cytotoxic T cells, and it enhances activation and proliferation of T cells, B cells, and natural killer cells.
Clonal Selection Cytotoxic T Cells (cells that kill cells)
oClonal Selection:activated cytotoxic T cell undergoes clonal selection to form a clone of cytoxic T cells:
•Active Cytotoxic T cells: attack other body cells that have been infected with the antigen
•Memory Cytotoxic T cells: Available for swift response if a second exposure should occur
How do Cytotoxic T cells kill infected cells
1.Releasing Granzymes: Protein-digesting enzymes that trigger apoptosis ( death of cells )
2.Releasing proteins from their granules
- Perforin: creates channels in the plasma membrane of a target cell causes cell lysis. (the dissolution or distruction of cells)
- Granulysin: Enters through the channels and destroys the microbes by creating holes in their plasma membranes
3.Secreting Lymphotoxin that activates enzymes in the target cell causing its DNA to fragment ( therefore it can no longer replicate)
4.Secrete gamma-interferon to activate phagocytic cells
Ways to acquire adaptive immunity
