Chapter 17: Adaptive Specific Host Defenses Slides Flashcards
What are the agranulocytic lymphocytes of the adaptive immune system?
T cells
B cells
Natural Killer cells (NK)
What are the two types of adaptive immune responses?
Cell-mediated immune response
Antibody immune responses which includes the humoral immune response.
What is an antigen?
A molecule that is recognized by a specific antibody or the T-cell receptor (TCR) on a T cell.
What macromolecule is usually an antigen?
Protein.
What is an epitope?
A discrete part of antigen that antibody/TCR recognizes.
Which are mores specific PAMPs or antigens?
Antigens.
What are exogenous antigens?
Include toxins and other components of microbial cell walls, membranes, flagella, and pilli.
What are endogenous antigens?
Produced by microbes that reproduce inside a body’s cells.
What are auto-antigens?
Usually a normal protein or complex of proteins that is recognized by the immune system of patients suffering from a specific autoimmune disease. Derived from normal cellular processes.
How can T cells recognize an antigen?
T cells can only recognize antigen through Major Histocompatibility Complex (MHC).
What are the two classes of MHC?
MHC I and MHC II.
They have different roles and are found on different cells.
What are CD 4 + T cells?
Helper T cells.
What antigen complex do CD 4+ T cells recognize?
MHC II
What antigen complex do CD 8+ T cells recognize?
MHC I
What are CD 8+ T cells?
Cytotoxic T cells.
Where are MHC II receptors found?
They are found on immune cells; specifically macrophages, dendritic cells, and B cells.
What is the MHC II antigen derived from?
Derived from previously phagocytized material (bacteria, viruses, proteins).
What is the role of helper T cells?
To coordinate the immune response by the secretion of different cytokines.
What is the primary role of cytotoxic T cells?
They remove intracellular pathogens by inducing apoptosis.
What are the two pathways that cytotoxic cells use to induce apoptosis?
Perforin-granzyme pathway and CD95 pathway.
What is synthesized during the perforin-granzyme pathway?
Involves the synthesis of special killing proteins.
How does the perforin-granzyme pathway work?
Perforin punches a hole in the membrane and creates a complex (pore in the membrane).
Granzymes activate apoptotic enzymes that induce apoptosis.
How does the CD95 pathway work?
CD95L (T cells) makes a bridge with CD965 to the virally infected cell.
Enzymatic portion of CD95 becomes active, which activates enzymes to induce apoptosis.
What cells are MHC I made by?
All cells except RBCs because they do not have a nucleus.
What is the first step of CD4+ T cell activation?
TCR binds to MHC-II with recognized antigen and the T cell becomes primed.
What is the second step of CD4+ T cell activation?
The second co-stimulation signal occurs with additional APC and TCR signaling complexes.
True or False: MHC-1 and CD8+ T cells allow for detection and clearance of infected walls.
True
What is MHC-I antigen derived from?
The cytoplasm of infected cells.
What things are being loaded into the MHC-I antigen?
Antigen from proteins being degraded and recycled from the cytoplasm.
True or False: MHC-I antigen can be derived from intercellular pathogens but not host-derived.
False; it can be both.
What is the first step of CD8+ T cell activation?
1st signal occurs upon TCR binding to MHC-I with recognized antigen and causes an increase in IL-2 receptors.
What is the second step of CD8+ T cell activation?
Second signal occurs when a CD4+ T cell is stimulated via MHC-II and secretes IL-2, which binds to IL-2 receptors on CD8+ T cells.
Where can you find B cells and antibodies in the body?
The spleen, lymph nodes, and MALT (Mucosa-associated lymphatic tissue). A small amount circulates in the blood.
What is the major function of B cells?
The secretion of antibodies.
True or False: Each B cell generates a single BCR that recognizes only one epitope.
True.
What forms the antigen-binding sites of BCRs?
Two variable regions.
What are the specific cells antibodies are secreted from?
Plasma cells.
What are antibodies?
Immunoglobulins similar to BCRs.
True or False: Plasma cells have antigen-binding sites and antigen specificity identical to the BCR of the activated B cell.
True.
Where are antibodies found?
Serum or mucosal secretions.
What are the 5 major antibody categories?
IgG, IgA, IgM, IgD, and IgE.
What is the IgM antibody?
It is pentameric in shape and is first produced in humoral immune response.
What is the IgA antibody?
It forms dimers, is the primary type found in secretions.
What is the IgG antibody?
It is monomeric in shape and is the primary type found in blood and extracellular fluid.
What is the IgE antibody?
It is monomeric in shape and has low levels in blood and extracellular fluid, mainly found in tissue bound by mase cells and participates in allergic reactions.
What is complementary to epitopes?
Antigen-binding sites.
What are the different functions of antibodies?
Activation of complement and inflammation
Neutralization
Opsonization
Killing by oxidation
Agglutination
Antibody-dependent cellular cytotoxicity (ADCC)
What is neutralization?
When antibodies block the toxins of bacteria and viruses so they cannot bind and cannot replicate.
What is opsonization?
Macrophages can recognize the Fc receptor protein in antibody and makes it want to eat it more.
What is oxidation?
Converting molecular oxygen into hydrogen peroxide to kill the bacterial cell.
What is agglutination?
When antibodies connect bacterial cells all together, stopping them from getting into the bloodstream or deeper tissue.
What is antibody-dependent cell-mediated cytotoxicity?
NK cell binds to Fc receptor protein of antibodies.
Perforin allows granzyme to enter, which triggers apoptosis and lysis.
What does the initiation of the complement system do?
Promotes the inflammatory response, recruiting phagocytes to site of infection, enhancing phagocytosis by opsonization, and killing gram-negative bacteria pathogens with the membrane attack complex (MAC).
What are the two steps of T cell-dependent B cell activation?
Binding directing to antigen (phagocytize antigen).
Present antigen via MHC II (second signal comes from helper T cells (CD4+) (TH2)).
What is special about the B cells formed from T cell-dependent B cell activation?
They are the only B cells that can form memory.
What are the two steps of T cell-independent B cell activation?
T1-T1 Antigen stimulation with PRR stimulation (at the same time).
T2-T2 Antigen that directly stimulates B cells (Often contains repeating subunits).
What are plasma cells?
Fully matured B cells.
What do plasma cells do?
Secrete anitbodies.
What happens first after the B cells are activated?
They proliferate through clonal expansion which is when B cells clone themselves and differentiate.
Where do B cells develop?
The bone marrow.
Why do BCRs have massive diversity?
A complex series of gene-slicing events.
True or False: Only 10% of B cells make it out of the bone marrow.
True
When is a B cell called an immature B cell?
After gene rearrangement and expression of unique BCR cell.
What happens if the BCR reacts with its antigen during the immature B cell stage?
Apoptosis.
Why does apoptosis occur if BCR reacts with its antigen?
It prevents the release of self-reactive B cells.
Why does apoptosis occur if BCR reacts with its antigen?
It prevents the release of self-reactive B cells.
What type of antibody do all B cells secrete first?
IgM.
What is isotype switching?
A splicing event in B cell DNA which can result in changes to the Fc region but leaves the variable region unchanged.
When does isotope switching occur?
After B cell activation.
What is the new isotype dependent on?
Cytokine signals.
During isotype switching, which class of antibody do you want lots of?
IgG.
What is affinity maturation?
After activation B cells increase the mutation rate of the genes encoding for the variable region (antigen binding) f the BCR and therefore antibody.
What does affinity maturation result in?
Some B cells will have higher affinity for an antigen.
What does the higher affinity do for B cells within the germinal center (site within lymph nodes/spleen)?
It increases the amount of stimulatory signals given to these B cells.
Where do the stimulatory signals in the germinal center come from?
Dendritic cells presenting antigen.
What does the increase of stimulatory signals to B cells in the germinal center do?
Increases the rate of growth of these high-affinity cells.
What are some characteristics of memory B cells?
Long-lived
Easier to induce antibody secretion
Produce IgG
High affinity for antigen
Provides immunity
True or False: B cells that have undergone affinity maturation are not more likely to become memory B cells.
False.
Where do all leukocytes come from?
The bone marrow.
What cells migrate from bone marrow to the thymus?
Prothymocytes (T cell precursors).
What do the thymocytes lack upon arrival to the thymus?
TCRs, CD4, and CD8.
True of False: Quickly upon arriving at thymus the thymocytes express CD4, CD8, and TCRs.
True.
True or False: Most thymocytes will not survive and 95%-99% will be “weeded out”.
True.
What is the cortex of the thymus?
The dense outer region.
What is the medulla of the thymus?
The looser inner region.
What are the epithelial reticular cells in the thymus?
Macrophages, dendritic cells and epithelial cells there to teach the T cells.
What is the first round of selection for T cells?
Positive selection, where T cells must recognize MHC I or MHC II with or without peptide.
What happens if the T cells don’t recognize MHC I or MHC II?
They die.
What happens to the T cells that interact with MHC I?
They quickly stop expressing CD4.
What happens to the T cells that interact with MHC II?
They quickly stop expressing CD8.
What is the second round of T cell selection?
Negative selection where T cells interact with antigen-presenting cells which present self-antigen.
What happens if a T cell binds to and recognizes self-antigen?
They are eliminated.
