Exam IV Flashcards
What is MHC?
Major Histocompatibility Complex protein
Where is MHC located?
On the surface of plasma membrane of cells
Which type of T cells do MHC class I and MHC class II interacts with?
MHC Class I = Tc and CTL cells MHC class II = Th cells.
What happens when an MHC class I protein is bound to an antigen?
It interacts with a Tc or CTL cell
What happens when an MHC class I protein is not bound to an antigen?
It keeps NK cells from killing the cell.
What type of cells are MHC class II proteins found on?
APC cells including dendritic, macrophages and B cells.
On what type of cells are MHC class I proteins found on?
On all cells.
When an MHC class II protein is bound to an antigen, what does it do?
Interacts with Th cells.
What is TCR?
T cell receptor.
What does a TCR do?
A TCR (T cell receptor) is used by T cells to interact with antigens displayed by MHC.
What is used by T cells to interact with antigens displayed by MHC?
TCR (T cell receptor)
What are CDs?
Clusters of differentiation
What are clusters of differentiation (CDs) used for and what are the types?
CDs are co-receptors that help T cells distinguish between MHC I and II proteins.
CD4 and CD8
What is CD4 used for?
CD4 is a cluster of differentiation that is found on Th cells to distinguish MHC class II cells.
What cluster of differentiation is found on Th cells to distinguish MHC class II cells?
CD4
What is CD8 used for?
CD8 is a cluster of differentiation that is found on Tc cells and recognizes MHC class I proteins.
What type of cluster of differentiation is found on Tc cells and recognizes MHC class I proteins?
CD8
Th are what?
T helper cells
What do T helpers do?
Th cells recognize an antigen presented by an APC on an MHC class II protein.
What type of cell recognizes an antigen presented by an APC on an MHC class II protein?
T helper
What do cytotoxic T cells do?
Tc cells recognize an antigen presented by an APC on an MHC class I protein (all cells).
What cells recognize an antigen presented by an APC on an MHC class I protein (all cells)?
Cytotoxic T cells (Tc)
What do activated T helper cells do?
Divide and differentiate into several cell types, including memory cells.
What type of T cell when activated divides and differentiate into several cell types, including memory cells?
T helper cells
What do activated cytotoxic T cells do?
Differentiate into CTLs (Cytotoxic T lymphocytes).
What type of cells differentiate into CTLs (Cytotoxic T lymphocytes) when activated?
Cytotoxic T cells (Tc)
What class of MHC protein are CTLs associated with?
MHC class I
What do CTLs do?
CTLs recognize antigens displayed by MHC class I proteins on the surface of a cell.
What happens when a CTL attaches to cell?
Releases:
Perforin (pore-forming protein)
granzymes and proteases that cause apoptosis (programmed cell death)
What cells release: Perforin (pore-forming protein) Granzymes Proteases That cause apoptosis (programmed cell death)
CTLs
When does a cytotoxic T cell become a CTL?
When the Tc recognizes the antigen displayed by an MHC class I cell, it differentiates into a cytotoxic T lymphocytes (CTL).
What are B cells covered with?
One type of antibody: IgD
What do B cells do?
IgD antibody binds to antigen.
B cell presents to T helper cells
B cell becomes activated by Th cells
B cell divides and differentiates into memory and plasma cells.
What do B memory cells do?
Remain dormant until exposed to antigen in the future. Then divide and differentiate into plasma cells when exposed to the antigen in the future.
What do plasma cells do?
Produce lots of antibodies and secrete them into the blood.
Where do plasma cells secrete antibodies?
Into the blood
What do memory B cells do when exposed to the antigen for which they were first made?
They divide and differentiate into plasma cells.
Memory B cells are long lived? T/F
True
What cells are long lived and can divide and differentiate into plasma cells at a later date when exposed to the same antigen?
Memory B cells
What is an epitope?
The part of an antigen that binds to a specific antigen receptor on a B cell.
What is a part of an antigen that binds to a specific antigen receptor on a B cell?
An epitope.
What are immunoglobulins?
Antibodies.
What initiates B cell activation?
The antibody (immunoglobulin) on the B cell surface binds to the epitope (specific receptor on the antigen) and both antigen and antibody are taken into the B cell.
What happens to the antigen/antibody complex once it’s taken into a B cell?
It is processed into smaller pieces and then a fragment of the antigen is presented on the B cell surface on an MHC class II protein to attract a T helper cell. Then the Th cell produces cytokines that activate the B cell.
What type of antibody do plasma cells secrete large amounts of?
IgG specific to the activated B cell
What type of cell produces large amounts of IgG antibodies?
Plasma cells
What do antigens need to have to stimulate B cells without Th cells?
Repeating subunits that can bind to multiple B cell receptors
What can antigens that have repeating subunits do when binding to multiple B cell receptors?
Eliminate the need for T helper cell activation of the B cell.
What do all of the activation methods of the complement system lead to activation of?
C3
What are opsonins?
Antibodies or other substances that bind to antigens making them more susceptible to phagocytosis (IgG antibodies and the C3b molecules of the complement system).
What is opsonization?
A process where antigens are marked for phagocytosis.
What happens to C3 to activate it?
C3 is cleaved into C3a and C3b.
What does C3b do?
As the activated part of C3:
C3b binds to an antigen surface to aid in attachment of phagocytes (opsonization)
C3b cleaves C5 into C5a and C5b
What do C3a and C5a do?
Bind to mast cells and stimulate the release of histamine and other chemicals to increase vessel permeability during inflammation.
In the complement system, what happens to C5b, C6, C7 and C8?
C5b, C6, C7 and C8 bind together (form a complex) and insert into the membrane of bacterial cells.
What does the C5b, C6, C7 and C8 complex act as?
Acts as a receptor that attracts C9.
How does C9 behave in the complement system?
Multiple C9 fragments form a transmembrane channel. C9 fragments, together with the C5b, C6, C7 and C8 complex, form the MAC (membrane attack complex).
What is the MAC and what does it do?
The MAC (membrane attack complex) is an end product of the complement system whereby the C5b, C6, C7 and C8 complex and the C9 fragments join forces. This acts as a channel which leads to cytolysis of the bacterial cell.
What are the protective outcomes of each part of the complement system?
Opsonization: C3 cleaves into C3a and C3b, where C3b binds to membrane of microbe (opsonin) to facilitate attachment of phagocytes.
Inflammation: C3a and C5a bind to mast cells and stimulate histamine release to increase vessel permeability during inflammation.
Cytolysis: C5b, C6, C7 and C8 combine with C9 fragments to create the MAC (membrane attack complex) that acts as a channel into the bacteria cell which leads to cell lysis.
Define each protective outcomes of the complement system.
Opsonization: C3 cleaves into C3a and C3b, where C3b binds to membrane of microbe (opsonin) to facilitate attachment of phagocytes.
Inflammation: C3a and C5a bind to mast cells and stimulate histamine release to increase vessel permeability during inflammation.
Cytolysis: C5b, C6, C7 and C8 combine with C9 fragments to create the MAC (membrane attack complex) that acts as a channel into the bacteria cell which leads to cell lysis.
What system do opsonization, inflammation and cytolysis signify?
The complement system
What are three ways the complement system can be activated?
Classical, alternative and lectin pathways
What controls the classical activation pathway of the complement system?
Antibodies
What happens in the classical activation pathway of the complement system?
Antibodies attach to antigens on the surface of the microbe.
When antibodies attach to antigens on the surface of microbes, what is recruited in the classical pathway of the complement system?
C1
C1 cleaves C2 to C2a and C2b and C4 to C4a and C4b
C2a and C4b combine and activate C3 by cleaving it into C3a and C3b
What has to happen at the end of each pathway–classical, alternative and lectin–of the complement system to achieve activation?
C3 must be cleaved into C3a and C3b
What substances are employed in the alternative pathway of the complement system?
Protein factors, specifically Factor B, factor D and factor P
To what system are Factor B, factor D and factor P important?
The alternative pathway of the complement system
What are lectins?
Proteins that bind to carbohydrates found on the surface of microbes.
What are lectins produced by and when are they produced?
Lectins are produced by the liver in response to cytokine release by macrophages after they ingest bacteria, viruses or foreign matter.
When do macrophages release cytokines?
After they ingest microorganisms or foreign matter.
Are lectins specific to certain carbohydrates?
Yes, specific lectins bind to specific carbohydrates.
What is an example of lectins that bind to a specific carbohydrate?
Mannose-binding lectin binds to the carb mannose found in cell walls and viral particles. It cleaves C2 and C4, C2a and C4b combine to split C3 into C3a and C3b (as in the classical pathway).
In the complement system alternative pathway, how do the protein factors activate C3?
Protein factors B, D and P recruit C3 and cleave it into C3a and C3b.
What do the classical and lectin pathways of the complement system have in common when activating C3?
The classical starts with C1 and the lectin starts with C2, but they both cleave C2 and C4 and end with C2a and C4b combining to cleave C3 into C3a and C3b.
In the complement system, how does the alternative pathway differ in the activation of C3 from the classical and lectin pathways?
The alternative pathway protein factors directly recruit C3 and cleave it into C3a and C3b.
Name three ways that microbes evolved to avoid the complement system.
Capsules that can prevent complement activation.
Sialic acid in capsules discourages opsonization and MAC formation.
Some gram + cocci release an enzyme that breaks down C5a (w/ C3a binds with mast cells) which stops the activation cascade.
Capsules, sialic acid, and gram + cocci enzymes are examples of what?
Ways in which microbes have evolved to avoid the complement system.
What is the innate immune system?
That part of the immune system that people are born with that does not depend on B or T cells. It includes the 1st and 2nd lines of defense.
Granulocytes and agranulocytes are involved in what segment of immunity?
Innate - 2nd line of defense
Name 3 types of granulocytes
Neutrophils, eosinophils, basophils
What is a neutrophil?
A type of granulocyte that is highly phagocytic and motile, can leave the blood and travel into the tissues to destroy microbes and foreign particles.
What is a basophil?
A type of granulocyte that releases histamine for the inflammation and allergic response.
What is an eosinophil?
A type of granulocyte that has phagocytic properties and can leave the blood (like neutrophils). Major function is to produce toxic proteins to defend against parasites (like helminths).
How do eosinophils attack parasites?
Attach to the surface of the parasite and discharge peroxide ions and digestive enzymes.
Name three types of agranulocytes.
Monocytes, dendritic cells and lymphocytes.
What types of blood cells are highly phagocytic?
Neutrophils and macrophages
Is a monocyte phagocytic?
Not actively phagocytic until it matures into a macrophage.
What is a monocyte?
A slightly phagocytic agranulocyte that matures into a macrophage when leaving the blood and entering the tissues.
What are macrophages?
Highly phagocytic antigen presenting cells that matured from monocytes in the blood when they entered the tissues. Have MHC class II proteins on membrane that interact with T helper cells.
What is a dendritic cell?
An agranulocyte with long extension like a nerve cell that destroy microbes by phagocytosis and initiate adaptive immunity responses. Have MHC class II proteins on plasma membrane that interact with T helper cells.
What are lymphocytes?
Agranular blood cells that include NK cells that check for non-self cells (MHC class I - Tc cells), T cells that regulate adaptive immune response and are responsible for cellular immunity, and B cells that produce antibodies in humoral or antibody-mediated immunity in adaptive immunity.
NK, B and T cells are what type of blood cells?
Lymphocytes
List 5 classes of antibodies
IgG, IgD, IgE, IgA, IgM
What are IgG antibodies?
IgG are monomers produced by plasma cells (most common - 80%)
What are IgD antibodies?
IgD are monomers similar to IgG found on B cell surface in blood and lymph. Involved in immune response initiation in B cells.
Which antibody is responsible for immune response initiation in B cells?
IgD, because they cover B cell surface membrane.
What are IgE antibodies?
Monomers slightly larger than IgG, very rare in serum. Fc (stem) of IgE bound to receptors on mast cell and basophils (allergic rxs). Binding of IgE to attached cell releases histamine and mediators to provoke an allergic response.
What are IgM antibodies?
Pentameter - Five monomers joined by polypeptide J chain. Causes clumping of bound antigens (agglutination).
Many antigen-binding sites.
Appear first in immune response and are short lived.
What antibody appears first in an immune response and is short lived?
IgM
What antibody is a pentameter?
IgM
What antibody that binds to a cell releases histamine?
IgE (mast cells and basophils)
What antibody causes agglutination?
IgM - the pentameter
Which antibody has many antigen-binding sites?
IgM
Which antibodies are most common?
IgG
What antibodies are produced by plasma cells?
IgG
What is an IgA antibody?
Two monomers joined by J chain a polypeptide called secretory component that protects IgA from enzymatic degradation. Most common in secretions (mucus, saliva, tears and breast milk). Protects newborns from gastrointestinal infection.
What antibody is made of two monomers?
IgA
What antibody has a polypeptide called secretory component and what does it do?
IgA, protects IgA from enzymatic degradation.
What type of macromolecule is secretory component of IgA antibodies?
Polypeptide
What is the most common antibody in bodily secretions including breast milk?
IgA
Which antibodies are monomers?
IgG, IgE, IgD
Which antibodies are not monomers?
IgM - pentameter
IgA - two monomers
What antibody is found on the surface of B cells?
IgD
What is an antigen?
Anything that causes antibody formation.
What is anything that causes antibody formation?
An antigen
What macromolecules are most antigens made of?
Polypeptides (large proteins) or polysaccharides.
What region of an antigen do antibodies interact with?
The epitope or antigenic determinant.
What is the antigenic determinant?
The epitope or the region of an antigen that antibodies interact with
What is the relationship between antibodies and antigens?
Antigens have an epitope or antigenic determinant that is recognized by and interacts with the antibody.