Immunology 3 - Initiation of Acquired Immune Responses Flashcards
Where do B cells mature?
Bone marrow
What cells are responsible for humoral immune responses?
B cells
What are “humors”?
Body fluids
What do B cells produce?
Antibodies
Where do T cells mature?
Thymus
What are antibodies?
Proteins that bind to one specific antigen
What are antibodies a complex of?
Four polypeptide chains - two light chains and two heavy chains
How can antigens cause an adaptive immune response?
Activating B and T cells
What are antibodies also known as?
Immunoglobulins
What is the part of the antigen that an antibody attaches to called?
Epitope
What does BCR stand for?
B cell receptor
What are the five classes of antibodies?
IgM, IgG, IgA, IgE, IgD
What is the difference between PAMPs and antigens?
There are a limited number of PAMPs, which are common to many different pathogens
Antigens are unique to an individual pathogenic species
What is an antigen?
A substance which can cause an adaptive immune response by activating B and T cells
What are sites where T and B cells are activated by antigens?
Secondary Lymphoid Tissues
Where do inactive T and B cells circulate between?
The blood, secondary lymphoid tissues and lymphatic vessels
What class of antibodies is used to bind to B cells’ target antigens?
IgM or IgD
What do B cells do once activated?
Multiply and differentiate into plasma cells and memory B cells
What do plasma cells do?
Produce and secrete soluble, antigen specific antibodies
What are memory B cells?
Long lived cells that continue to circulate around the body
What process do naive B and T cells use to enter the lymph nodes?
Transendothelial migration
Where do naive T and B cells enter the lymph nodes from?
High endothelial venules (HEV)
What does opsonise mean?
To make a cell more susceptible to phagocytosis
How does a B cell encounter antigens?
An opsonised antigen travels to the B cell zone
Eventually the right B cell will come and bind to the opsonised antigen
Where are B cell zones located?
Lymph nodes
What needs to happen for a B cell to become fully activated?
It must receive two signals:
An antigen
‘Helping’ signals
What is the other signal a B cell must receive to become activated when the antigen is a protein?
A help signal from a helper T cell
What is the other signal a B cell must receive to become activated when the antigen is not a protein?
A PRR binding to a PAMP
What must happen for a B cell to become activated when the antigen has repetitive antigenic epitopes?
Multiple BCR and antigens must be engaged
What do the daughter cells of B cells form?
A secondary follicle within the B cell zone called the Germinal Centre
What antibodies are first produced by short-lived plasma cells?
IgM
What affinity are IgM antibodies?
Low
What classes of antibodies are produced after IgM
IgG, IgA, IgE
What kind of antigens are B cells that secrete IgG antibodies reacting to?
Protein antigens
What affinity are IgG antibodies?
High
Why does the antibody level have a lag period?
The process of B cells becoming activated, dividing, differentiating and producing antibodies takes time
When are the highest levels of antibodies?
7-10 days after infection
What two functions do antibodies have, which part of the antigen performs that function, and what is involved?
Recognition function - Variable region sites - Binding to antigen Effector function - Heavy chain constant region - Clearance mechanisms to inactivate to eliminate the microbe
What are the functions of IgM antibodies?
B cell activation
Agglutination
Complement system activation
What is agglutination?
The formation of immune complexes
What does the Ig mean in the names of the classes of antibodies?
Immunoglobulin
Where is IgM present and why is it there only?
Plasma and secretions
It is too large to enter tissues
What is the process of agglutination?
Antibodies cross-links multiple antigens to produce clumps of antigens
What is agglutination mediated by?
Specific antigen binding to IgM and IgG antibodies
How does agglutination help to eliminate pathogens?
Enhances phagocytosis
Prevents viruses from binding to and infecting host cells (neutralisation)
Which classes of antibodies activate the complement system?
IgM
IgG
How do antibodies activate the complement system?
Specific antigens bind to IgM and G receptors, inducing a change in conformation in the fc region.
This exposes multiple binding sites for C1, the first component of the classical activation pathway
What is the fc region of antibodies?
The tail region that interacts with cell surface receptors
What are the functions of IgG antibodies? (6)
Agglutination Complement system activation Foetal immune protection Neutralisation Opsonisation NK cell activation
What is the most abundant class of antibody and the dominant type produces during a secondary immune response?
IgG
Which class of antibody has the longest half life?
IgG
Which antibodies are transported across the plasma into the foetal blood circulation?
IgG
What is neutralisation?
The prevention of viruses from binding to and infecting host cells
The prevention of microbial toxins from disrupting normal cell function
Why is there a window when babies are at high risk of infection?
After birth babies are no longer being given IgG antibodies by the mother so IgG levels decline. Before IgM, G and A levels increase there is a window where the level of antibodies is low
What antibody classes cause neutralisation?
IgG
Secretory IgA
What is the structure of IgM antibodies?
Pentamers
What is opsonisation?
The process of coating pathogens in immune proteins called opsonins to enhance phagocytosis
Which class of antibodies are the most effective opsonins?
IgG
Which class of antibodies is the most effective activator of NK cells?
IgG
What are the functions of NK cells?
Killing of infected host cells
Production of pro-inflammatory mediators
What is the function of IgD antibodies?
B cell activation
In what form do IgD antibodies activate B cells?
Membrane-bound form
What is the second most abundant type of antibody?
IgA
What form of IgA antibody is present in serum?
Monometric form
What is the function of the monometric form of IgA antibodies?
Neutralisation
What are the functions of the dimetric form of IgA antibodies?
Neonatal defence
Neutralisation at mucosal sites
Where is the dimetric form of IgA antibodies present?
Secretory fluids
What is the shorthand for the IgA antibodies that are found in secretory fluids?
sIgA
Where are sIgA antibodies transported into and why?
Colostrum (colostrum and breast milk
To protect the GI tract of neonates
What is colostrum?
A form of milk produced by the mammary glands of mammals in late pregnancy
What can IgE antibodies trigger?
Allergic responses
Which antibody class(es) are involved in neutralisation?
IgM
IgG
IgA
Which antibody class(es) are involved in agglutination?
IgM
IgG
Which antibody class(es) are involved in opsonisation?
IgG
Which antibody class(es) are involved in complement activation?
IgM
IgG
Which antibody class(es) are involved in NK cell activation?
IgG
Which antibody class(es) are involved in placental transfer?
IgG
Which antibody class(es) are involved in B cell activation?
IgM
IgD
Which antibody class(es) are involved in allergic responses?
IgE
