PSIO202 Exam 2 Lecture 17-18 Flashcards
What is an aquired immune response?
immune response resulting from a specific foreign protein or antigen
What is an antigen?
toxin or other foreign substance which induces an immune response in the body, especially the production of antibodies
What are the two types of adaptive immunity?
cell mediated and antibody mediated
What are they key properties of complete antigens?
immunogenicity, reactivity
What is immunogenicity?
ability to stimulate an immune response, the proliferation of specific lymphocytes and antibodies
What is reactivity?
ability to initiate reactions with the activated lymphocytes and antibodies released in response to them
What are examples of complete antigens?
foreign proteins, nucleic acids, some lipids, and large polysaccharides
What is the difference in where cell-mediated and antibody-mediated immune responses take place?
cell-mediated: inside the cells
antibody-mediated: in body fluids
What makes receptors so specific?
They are composed of random rearrangements of a series of gene segments
How many receptors are on a lymphocyte?
10^5
The receptors are identical on a lymphocyte’s…
daughter cells
What are the three properties of an immune response?
tolerance, specificity, and memory
What is tolerance?
the ability to discriminate self from non-self
What is specificity?
receptors and antibodies recognize just ONE antigen
What is memory?
on re-exposure, the immune response is faster and more intense
What is notable about the immature lymphocytes in bone marrow?
they are all nearly identical
What are the two ways lymphocytes mature/are selected?
positive and negative selection pressure
What is positive selection pressure?
selecting FOR t lymphocytes that have a weak response to self antigens, thus being both immunocompetent and self-tolerant
What is negative selection pressure?
select AGAINST t lymphocytes that are strongly anti-self (would attack itself)
What percent of the t lymphocytes do NOT pass selection?
95%
What is a major histocompatibility complex?
a collection of genes coding for MHC molecules found on the surface of all nucleated cells of the body
What cells are the only ones which do not have an MHC expressed?
RBCs
How is an MHC expressed?
viral particle broken down into proteins, some of those proteins form an MHC which is expressed on the surface. T cells with a receptor look for the right MHC
Where does selection for t lymphocytes occur?
the thymus
How else can cytotoxic T cells be denoted?
CD8
How else can helpter T cells be denoted?
CD4
What determines which foreign substance our immune system will recognize and react to?
genes
Once immunocompetent lymphocytes are exported to secondary lymphoid tissue, what happens?
they encounter antigens and mature into fully functional antigen-activated cells
What types of structures do T lymphocytes recognize? (cytotoxic and helper)
High Specialty
peptides: small, only when they are presented on an MHC (has to come from inside the cell)
cytotoxic recognize MHC1
helper recognize MHC2
What types of structures do B lymphocytes recognize?
Broad Specificity
proteins, lipids, carbohydrates, nucleic acids, parts of macromolecules
large and diverse microbes and toxins
What is an epitope?
the region on an antigen which will bind to a T or B cell receptor
What is required for T cells to recognize an epitope?
It has to be on an MHC
What are the 5 steps for T lymphocyte immune response?
antigen presentation, antigen recognition, activation, proliferation/differentiation, and destruction
What are the three types of antigen presenting cells?
What is the best type?
dendritic cells, macrophages, and B lymphocytes
dendritic are the best
What is the role of antigen presenting cells in immunity?
engulf antigens (phagocytose and break down) and present fragments of the antigen on their surface for T lymphocytes to recognize
How are DC’s better functioning APC’s? What do they do that is special?
they actively migrate to the lymph nodes and secondary lymphoid organs and present antigens to T and B lymphocytes
What type of MHC will a cytotoxic T cell recognize, and what is that MHC located on?
cytotoxic recognize MHC1, which are located on any nucleated cell. They present antigens that infect the cell.
What type of MHC will a helper T cell recognize and what is that MHC located on?
helper T cells recognize MHC2, which are located on APCs
What type of MHC do APCs have on them?
both - MHC2 because they are an APC, but also MHC1 because they are nucleated
Give an overview of how a nucleated cell/MHC1 presents an antigen.
when an antigen is brought into the cell, it is broken down into peptides. Those peptides are taken into the ER through a transporter, and then given to the MHC1 waiting in the ER. The MHC1 binds the antigen peptide, and moves/inserts into the cell membrane to display the peptide for cytotoxic T cells
Give an overview of how an APC/MHC2 presents an antigen.
An antigen is phagocytosed and broken down into peptide fragments which are then packaged into a vesicle. A vesicle of MHC2 molecules fuses with the vesicle of peptides, and then inside the peptides bind to the MHC. Vesicle will exocytose the complex, which then inserts into the membrane to present to helper T cells.
What other protein is required for T lymphocytes to bind to an MHC/antigen complex?
helper T/MHC2 - CD4
cytotoxic T/MHC1 - CD8
What final step is required for only APCs/MHC2 antigen complexes to be recognized by a T lymphocyte?
co-stimulation by interleukins 1 and 12
Without co-stimulation of the APC’s MHC/antigen complex, what would happen regarding the T lymphocytes?
they would become tolerant to the antigen, would not secrete more cytokines, and would be unable to divide/proliferate
What happens to a T lymphocyte as a direct result of costimulation?
more cytokines are released, including IFN-gamma, interleukin 2, and more IL2 receptors
What happens to a T lymphocytes as a result of the cytokines which are released after costimulation?
IFN-gamma: stimulate more MHC2 on the APC
IL2: proliferation (clonal expansion) and differentiation (memory T and activated T)
What two things are stimulated when a helper T lymphocyte is exposed to an antigen?
proliferation of more T lymphocytes and B lymphocytes that are already bound to an antigen
What are the only cells that can directly attack and kill other cells? What do they target?
cytotoxic T lymphocytes
virus infected cells, cells with intracellular bacteria or parasites, cancer cells, foreign cells from blood transfusions or transplants
What are the two mechanisms of CTL action?
1) release granzymes which cause apoptosis, releasing microbes to be phagocytosed
2) insert a perforin ring which allows ISF in to lyse (burst) the cell, and then the microbes are destroyed by granulysin
