Chapter 15 Flashcards
How does adaptive immune response improve
The adaptive immune response improves after exposure to microbial invaders or other foreign materials (Antigens)
Antigen
Molecule that reacts specifically with either an antibody or an antigen receptor on a lymphocyte.
What happens when an antigen is first encountered
When an antigen is first encountered, certain lymphocytes recognize it and then proliferate (multiply quickly). This dramatically increases the number of the most effective lymphocytes, allowing efficient removal of the invader.
Adaptive immunity
Protection provided by immune responses that improve due to exposure to antigens, involved B cells and T cells.
What are the main participants in adaptive immunity
Lymphocytes
What is an important characteristic of the adaptive immune response
Molecular specificity, meaning that the recognition of the antigen is precise.
On first exposure to a given microbe, how long does adaptive immunity take
On first exposure to a given microbe or other antigen, adaptive immunity takes a week or more to build.
During the delay when adaptive immunity is being built, what does the body depend on
During this delay, the host depends on innate immunity for protection, which may not be sufficient to prevent disease.
What happens when the forming of adaptive immunity when innate immunity is in use
When the response is successful, components of it are retained so that a faster and more effective reaction occurs upon reexposure. The system learns how to effectively protect against the pathogen
Immunological memory
The immune systems ability to respond more quickly and more effectively upon reexposure to a given antigen.
What prevents many diseases today
Vaccination
Why does vaccination prevent many diseases today
Vaccination prevents many diseases by exposing a persons immune system to relatively harmless forms of a pathogen or its product.
What do vaccines trigger
The vaccine triggers an adaptive immune response, so that if the vaccine recipient is then exposed to the actual pathogen, the memory response eliminates that agent before the disease develops
Immune tolerance
Decrease reactivity of the immune system to a specific antigen
Self versus non self recognitiom
The immune systems ability to distinguish between normal host cells and invading microbes.
Why is the ability to develop immune tolerance important
The ability to develop immune tolerance is crucial because without it the immune system would routinely turn against the body’s own cells, attacking them just as it does invading microbes.
It would also regularly attack harmless substances like pollen.
What are the two interacting mechanisms involved in adaptive immunity for eliminating foreign material in the body
- Cell mediated immunity
- Humoral immunity
Cell mediated immunity (CMI)
Immunity involving a T cell response
What is cell mediated immunity also called
Cellular immunity
What type of invader do cell mediated immunity deal with
Deals with invaders residing within a self cell, meaning within one of the body’s own cells. These invaders include viruses and bacteria replicating within a self cell.
What kind of cells does CMI rely on
CMI relies on T lymphocytes or T cells.
T cells or T lymphocytes
Type of lymphocyte that matures in the thymus.
What are the two types of T cells involved with eliminating antigens:
- Cytotoxic T cells
- Heller T cells
Cytotoxic T cells (CTL)
Type of lymphocyte programmed to destroy infected or cancerous self cells.
What do cytotoxic T cells induce
Cytotoxic T cells are responsible for inducing apoptosis in self cells infected with viruses or are otherwise corrupt.
Helper T cells
Type of lymphocyte programmed to activate B cells and macrophages, and assist other parts of the adaptive immune response.
Humoral immunity
Immunity involving B cells and an antibody response.
What kind of invaders does the humoral immunity deal with
Humoral immunity eliminates microbial invaders and toxins that are not within a self cell, in other words, invaders in the blood or in tissue fluids.
What kind of cells are involved in humoral immunity
It involves B lymphocytes of B cells.
B cell or B lymphocytes
Type of lymphocyte programmed to make antibodies.
Where do B cells develop
B cells are a cell you that develops in the bone marrow in mammals.
Antibody
Y shaped protein that binds to antigen
What happens when antibodies bind to specific antigens
In doing so, they mark them as an invader to be eliminated.
T and B cells have what that allow them to recognize specific antigens
T and B cells have thousands of copies of a receptor on their surfaces that allow them to recognize specific antigens.
What specific region of B and T cells are responsible for recognition of specific antigens
A region of the receptor called an antigen binding site is responsible for that recognition.
What are the antigen receptors like on a single lymphocyte
The antigen receptors on a single lymphocyte are identical and therefore recognize the same antigen.
Because the body has hundreds of millions of different lymphocytes, the immune system can recognize a nearly infinite assortment of antigens.
T cell receptor (TCR)
Molecule on a T cell that enables the T cell to recognize a specific antigen.
What kind of antigens do T cell receptors only bind to
T cell receptors only bind an antigen presented by one of the body’s own cells, an interaction guided by a surface molecule called a CD marker.
T cell receptors only bind to antigens guided by what
Guided by a molecule called a CD marker.
Cytotoxic T cells have a CD marker called
CD8
Helper T cells have a CD marker called
CD4
B cell receptor (BCR)
Molecule on a B cell that enables the B cell to recognize a specific antigen; the receptor is a membrane bound derivative of the antibody that the B cell is programmed to make.
Are essentially membrane anchored version of y shaped antibody molecules that the B cell is programmed to make.
How do T cell receptors and B cell receptors differ
Unlike T cell receptors, B cell receptors bind free antigens (antigens not presented by one of the body’s own cells)
What happens when cell mediated and humoral immunity are misdirected
They can damage the body’s own tissues
To provide the immune tolerance necessary to prevent inappropriate responses, two sequential processes are used
- Central tolerance
- Peripheral tolerance
When does Central tolerance occur
This takes place as lymphocytes mature (T cells in the thymus and B cells in the bone marrow);
Central tolerance
It eliminates immature T and B cells found to recognize certain self molecules
When does Peripheral tolerance occur
This occurs after the lymphocytes mature.
Peripheral tolerance
It prevents T and B cells that were not eliminated during central tolerance from reacting against self or other harmless molecules.
Naive lymphocyte
A lymphocyte that has an antigen receptor but has not encountered the antigen recognized by the receptor.
Example of peripheral tolerance
A naive lymphocyte cannot react to an antigen until specific signals from another cell confirm that the antigen is a microbe or other potentially harmful material.
In the case of a naive T cell or B cell, the cell’s antigen receptor must bind the antigen and the confirmatory cell must provide the signal to indicate that a response is warranted.
What do some mechanisms of peripheral tolerance interfere with?
Some mechanisms of peripheral tolerance interfere with the body’s ability to destroy cancer cells, and medications that block these are now being used to treat certain types of cancer.
What happens once a naive lymphocyte receives a signal that a response is needed?
Once a naive lymphocyte receives the signals that a response is needed, it be becomes activated, meaning it can proliferate.
What do the descendants of activated lymphocytes become?
Some descendants of activated lymphocytes differentiate to become effector lymphocytes.
Other descendants become memory lymphocytes.
Effector lymphocytes
Differentiated descendant of an activated lymphocyte; its actions help eliminate antigen.
Descendants of activated lymphocytes, armed with the ability to produce specific cytokines or other protective substances.
Are short lived
Memory lymphocytes
Long lived descendants of activated lymphocytes that can quickly respond when a specific antigen is encountered again.
Primary response
The first adaptive immune response to a particular antigen
The response that marks the adaptive immune system’s first encounter with a particular antigen.
Secondary response (or memory response)
Enhanced immune response that occurs upon second or subsequent exposure to specific antigen, caused by the rapid activation of long lived memory cells.
What is responsible for the effectiveness of the secondary response?
Memory Lymphocytes
Dendritic cells
Antigen presenting cells that play an essential role in the activation of naive T cells.
How do dendritic cells help activate the appropriate naive T cells
- Dendritic cells first collect various antigens/ material that may have originated from invading microbes.
- Dendritic cells travel to regions where naive T cells gather and interact with T cells in a way that passes on info about the antigen.
How do dendritic cells simultaneously collect various antigens and interact with T cells?
- By presenting various pieces of the antigen and
- producing surface proteins called co-stimulatory molecules if the antigen being presented is microbial or otherwise represents “danger”
Cytotoxic T cells can differentiate to become
Cytotoxic T cell differentiate to become an effector form called Tc cell.
TC cell
Effector form of cytotoxic T cell; it induces apoptosis in infected or cancerous “self” cells; also called a CTL (cytotoxic T lymphocyte).
What happens once a cytotoxic T cell is activated?
Once a cytotoxic T cell is activated, it proliferates.
Some clones differentiate into TC cells.
TC cells then search for certain infected self cells- specifically any cells infected with the antigen the TC cell recognizes.
If one is encountered, the TC delivers a death package to that infected self cell- inducing it to go into apoptosis.
The invader is thus deprived of a host in which to multiply.
Meanwhile other clones become memory cytotoxic T cells that can respond quickly upon exposure to the same antigen.
What does helper T cells differentiate into
Helper T cells differentiate to become an effector form called TH cell.
TH cell
Effector form of a helper T cell; it activates B cells and macrophages, and releases cytokines that stimulate other parts of the immune system.
What happens once a helper T cell is activated?
- Once a helper T cell is activated, it proliferates.
- Some of the clones differentiate into effector form called TH cell.
- TH cells deliver cytokines to certain macrophages and B cells, activating them. TH cells also produce cytokines that direct and support other cells, including various T cells.
- Other clones become memory helper T cells that respond quickly if the same antigen is encountered again.
Regulatory T cell
Type of lymphocyte that helps control the immune response.
They aid in preventing an immune response
In most cases, what is required for activation of naive B cells?
TH cells
In humoral immunity, once a B cell becomes activated and proliferates, what happens?
Once a B cell becomes activated and proliferates, many of the clones differentiate to become plasma cells, which are effector B cells.
Plasma cell
Effector form of a B cell; it functions as an antibody secreting factory
What are the two functional regions of an antibody molecule?
- Two identical arms (Fab region)
- Single stem of the Y shaped molecule (Fc region)
Fab region (Fragment antigen binding) region
Portion of an antibody molecule that binds to the antigen
The “arms” of the antibody
Fc region
“Stem” portion of antibody.
It tags the antigen for rapid elimination by macrophages or other components of the immune system.
What is the resulting protection that occurs because of Antibody-Antigen Binding?
- Neutralization
- Opsonization
- Complement System Activation
- Immobilization and prevention of adherence
- Cross linking
- Antibody dependent cellular cytotoxicity (ADCC)
Neutralization
A toxin or virus particle coated with antibody molecules cannot attach to host cell and therefore cannot damage that cell
Opsonization
Phagocytic cells have receptors for the Fc portion of certain classes of antibody molecules, making it easier for the phagocyte to engulf antibody coated antigens.
Complement System Activation (as a result of antibody-antigen binding)
When multiple molecules of certain antibody classes are bound to a cell surface or other antigen, a specific complement system protein attaches to side by side Fc regions. This triggers the classical pathway of complement system activation, leading to production of the opsonin C3b, initiation of an inflammatory response and formation of membrane attack complexes.
Immobilization and prevention of adherence
Binding of antibodies to flagella interferes with a microbe’s ability to move; binding to pili prevents a bacterium from attaching to surfaces.
Cross linking
The two arms of an antibody can bind separate but identical antigen molecules, linking them. The overall effect is that large antigen antibody complexes form, creating big “mouthfuls” of antigens for phagocytic cells to engulf.
Antibody dependent cellular cytotoxicity (ADCC)
When multiple molecules of certain classes of antibodies bind to a virally infected cell or a tumor cell, that cell becomes a target for destruction by natural killer (NK) cells. The NK cell attaches to the Fc regions and then kills that cell.
Immunogenic
Refers to the relative ability of an antigen to elicit an immune response.
Epitopes
Region of an antigen recognized by antibodies and antigen receptors on lymphocytes.
Region where antibody, B cell receptor or T cell receptor binds to an antigen
What are most antigens
T-dependent antigens
T dependent antigens
Antigens that evoke an antibody response only with the participation of TH cells.
T independent antigens
Antigens that can activate B cells without the assistance of a TH cell.
What is an example of T- independent antigens
lipopolysaccharide (LPS) and molecules with identical repeating subunits like some carbohydrates.
Lymphatic system
Collection of tissues and organs that bring the population of B cells and T cells into contact with antigens.
Lymphatic (lymph) vessels
Vessels that carry lymph, which is collected from fluid that bathes the body’s tissues; also called the lymphatics
Lymph
Clear yellow liquid that contains leukocytes and flows within lymphatic vessels.
Clonal selection theory
Theory that explains the process in which a lymphocyte’s antigen receptor binds to an antigen, allowing the lymphocyte to multiply.
Thus the antigen determine which lymphocytes multiply.
Immature lymphocytes
The antigen specific receptors on these are not yet fully developed
Activated Lymphocyte
A lymphocyte that is able to proliferate because it has received the necessary signals and its antigen receptor has bound to an antigen
Effector lymphocytes
Differentiated descendant of an activated lymphocyte; its actions help eliminate antigen.
They are armed with the ability to produce specific cytokines or other protective substances.
Examples of Effector lymphocytes
Plasma cells are effector B cells
Tc cells are effector cytotoxic T cells,
TH cells are effector helper T cells
Memory lymphocytes
Long-lived descendants of activated lymphocytes that can quickly respond when a specific antigen is encountered again.
They are responsible for the speed and effectiveness of the secondary response.
At first exposure to an antigen, how long does it take for a protective response to develop?
10-14 days
Antigen presentation
Process in which animal cells display antigen on MHC molecules for TH cells to inspect.
How does the host cell do antigen presentation
The host cell does this by partly degrading (processing) the antigen to release its component fragments and then placing individual peptides into the groove of the proteins major histocompatibility complex (MHC) molecules.
Major histocompatibility complex (MHC) molecules
Host cell surface proteins that present antigen to T cells
What happens when a T cell recognizes and binds to a presented antigen?
When a T cell recognizes and binds to a presented antigen, the TCR is actually binding both the antigen (peptide fragment) and the MHC molecule simultaneously.
How are the TCR of conventional T cells?
Conventional T cells have a TCR composed of two different polypeptide chains, called alpha and beta, connected by a disulfide bond.
Variable region of TCR
Lot of variation is seen in the amino acid sequences of the domains farthest from the cell surface
This region accounts for the antigen MHC binding specificity
Constant region of TCR
The domain closest to the cell surface have a consistent amino acid composition and make up the constant region.
What are the two types of MHC molecules used to present antigen?
- MHC class I
- MHC class II
Major Histocompatibility class I molecules (MHC class I)
Molecules that cells use to present antigen to cytotoxic T cells
Major Histocompatibility Complex Class II molecules (MHC class II)
Molecules on the surface of antigen-presenting cells (APCs) that present antigen to helper T cells.
CD markers
Cell surface molecules that allow scientists to distinguish subsets of T cells and other white blood cells.
What do dendritic cells activate?
Dendritic cells activate T cells
Cytotoxic T cells only recognize antigens presented on what
Cytotoxic T cells only recognize antigens presented on MHC class I molecules
Helper T cells only recognize antigens presented on what
Helper T cells only recognize antigens presented on MHC class II molecules.
CD markers
Cell surface molecules that allow scientists to distinguish subsets of T cells and other white blood cells.
Cross presentation
Dendritic cells can place peptides from material they have taken up on both types of MHC molecules (class I and class II); this ability is called cross presentation.
What does cross presentation allow dendritic cells to do
Allows them to present the antigens to cytotoxic T cells as well as helper T cells.
What activated T cells?
Dendritic cells
Steps to activating T cells (beginning –> transported to secondary lymphoid organs)
- Immature dendritic cells reside in the skin and tissues must gather materials from those areas (by phagocytosis and pinocytosis)
- Dendritic cells used TLR and other PRRs to recognize microbes.
- If danger is present, they take up more material and enter lymphatic vessels, which transport them to secondary lymphoid organs where naive T cells gather.
Activation of dendritic cells- what do dendritic cells do in the secondary lymphoid organs
- The dendritic cells contact naive T cells; any dendritic cells that detected “danger” produce co stimulatory molecules to communicate the significance of the material to the T cells.
- Naive T cells that recognize antigen presented by dendritic cells displaying costimulatory molecules can become activated.
What happens to naive T cells that recognize antigen presented by a dendritic cell not displaying co stimulatory molecules?
They often become anergic (unresponsive) and eventually undergo apoptosis; this eliminates lymphocytes that might recognize autoantigens or other harmless material and is an important mechanism of peripheral tolerance.
What happens once naive T cells are activated by dendritic cells?
Once activated, a T cell proliferates eventually giving rise to effector cells.
Activated T cells also give rise to long lived memory cells.
