Humoral Immunity (Exam 2) Flashcards
(T/F) All antibody isotypes have the function to neutralize microbes and toxins.
True
What are the 3 ways antibodies can neutralize microbes and toxins?
- block microbe from getting through epithelial barrier
- block microbe binding to host cell
- block toxin from binding to cell receptor
List the 5 antibody isotypes.
IgG
IgA
IgM
IgE
IgD
What is the major function of IgM?
activate complement (classical pathway)
List the 5 major functions of IgG.
- opsonization + phagocytosis
- activate complement (classical path)
- cytotoxicity (NK cells)
- neonatal immunity
- feedback inhibition of B cell activation
What is the major function of IgA
- mucosal immunity (GI + respiratory)
Where does IgA function to neutralize microbes?
in lumen of mucosal organs
What are the 2 major functions of IgE?
- helminth defense
- mast cell degranulation
What is the function of IgD?
functions as antigen receptor on B cells (not well known)
_____ receptors are proteins on cell surfaces that recognize specific ____ regions on antibodies to help with immune response.
Fc
Fc (constant)
(T/F) Free or circulating antibodies are activated by Fc receptors.
False - antigen-bound
What two antibody isotypes are involved in the two major types of antibody dependent cell-mediated cytotoxicity?
IgG
IgE
In the IgG cytotoxicity process, Fc regions on IgG are recognized by _____ receptor on ______ cells which kills antibody-coated cells.
Fcy (gamma)
NK cells
In IgE cytotoxicity process, IgE binds to _______ and Fc regions on IgE are recognized by ____ receptor on _______ which cause death when they release granules.
helminth parasites
Fce (epsilon)
eosinophils
What are the 3 complement pathways?
- classical
- alternative
- lectin
How is the classical complement pathway activated?
when antibody binds to antigen (IgG + IgM)
How is the alternative complement pathway activated?
on microbial cell surface w/o antibody
How is lectin complement pathway activated?
plasma lectin binds to mannose receptors on microbe surface
What are the C3 convertases for each complement pathway?
classical & lectin: C4b + 2a
alternative: C3b + Bb
Why does soluble IgG not activate complement?
only has one Fc region
What must occur for IgG to activate complement?
must bind to cell surface (then adjacent IgG Fc regions can bind complement)
(T/F) Both soluble IgM and IgA cannot activate complement.
False- IgM + IgG cannot
Why can soluble IgM not activate complement?
Fc regions are pentameric so not accessible to complement
What must occur for soluble IgM to activate complement?
binds to cell surface and then can change conformation
What does MAC stand for?
membrane attack complex
What is Membrane Attack Complex?
protein complex (of different complements) that can lyse cells
MAC is the (first/last) step in complement activation.
Last
Which complements (in order of formation) bind together to form MAC?
C5b, C6, C7, C8, C9
List the 3 major functions of complement.
- opsonization + phagocytosis
- inflammation
- cytolysis
In terms of complement’s function to opsonize and phagocytize microbes: cell -bound ______ is an opsonin which promotes phagocytosis of coated cells.
C3b
What 3 proteolytic products stimulate leukocyte recruitment and inflammation (one of the functions of complement)?
C5a, C3a, C4a
One function of complement is cytolysis via ________.
MAC (membrane attack complex)
_____ is transported through epithelial cells to neutralize microbes before they invade the epithelium.
IgA
IgA binds to ______ receptor and then is transported through the epithelial cell. Proteolytic cleavage occurs which allows it to become released into the lumen.
Poly-Ig
