13 - Effector Responses Flashcards
What are the effector molecules of humoral immunity?
antibodies
What are the effector cells of the cell-mediated immunity?
CTLs
What are the ways that humoral immunity is carried out?
neutralization | opsonization | agglutination | complement activation | antibody-dependent cell-mediated cytotoxicity (ADCC) | degranulation
What is the neutralization aspect of humoral immunity?
neutralizes toxins, pathogens, or proteins and blocks them from doing its job
What is the agglutination aspect of humoral immunity?
antigen/antibody complex enhances neutralization and clearance from body
What is the opsonization aspect of humoral immunity?
antibody bound to pathogen also binds to Fc receptor = macrophage will recognize this complex (due to FcR) and phagocytose pathogen
What is the complement activation aspect of humoral immunity?
involves MAC complex
What is the antibody-dependent cell cytotoxicity aspect of humoral immunity?
activates NK cells and CTLs
What is the degranulation aspect of humoral immunity?
Fc receptor-mediated | IgE degranulates granulocytes to release contents onto pathogen
What are the 5 characteristics of IgM?
first Ab activated | pentamer if secreted | membrane-bound on B-cells | lower affinity to antigen = 10 Ag binding sites | activates complement
What are the main roles of IgM?
opsonization | antigen/antibody complex formation
What are the characteristics of IgG?
only one to cross placenta | most prominent | all bind to Fc receptors
What are the 3 main roles of IgG?
activate macrophages | induce complement | mediates cell cytotoxicity (ADCC)
What are the 6 characteristics of IgA?
found in mucosal secretions | not fix complement = no inflammation | protease-resistant | dimer | not bind to FcR | mom passes this Ab on to fetus
What are the 2 main roles of IgA?
neutralizes toxins/pathogens | cross mucosal surfaces
What are the 6 characteristics of IgE?
allergy and worm infections | asthma |
What is the main role of IgE?
degranulation of granulocytes = release molecules to damage large pathogens
What are the 6 characteristics of IgD?
least common | membrane-bound and secreted | present in upper lung secretions
What are the 2 main roles of IgD?
binds basophils and mast cells | stimulates release of antimicrobial peptides
What is the function of Fc receptors?
induce effector reaction onto cell via signaling cascade
How are FcRs activated?
antibody binding and FcRs need to be “cross-linked” (bringing in multiple FcRs together)
What do FcRs use to initiate a signaling cascade and why?
ITAM and ITIM regions | don’t have a cytoplasmic tail region
What do ITAMs do?
induces phosphorylation of certain regions
What are ITIMs?
suppress immune responses of the co-receptors for FcRs
Which part of the antibody carries out the immune response? What is it determined by?
constant region = determined by antibody isotype
What is a key feature of FcRs that helps antibodies stick to them?
immunoglobulin domains
Where are PolyIgR expressed?
expressed on epithelial cells (not immune cells)
What are the 3 characteristics of Fc-gamma-R?
most diverse FcRs | binds to IgG | most are activating receptors = ITAMS
What is the main role of FcgR?
induce phagocytosis
What are the characteristics of FceR?
binds to IgE | ONLY found on mast cells/eosinophils/basophils
What is the main role of FceR?
degranulation of granulocytes
What happens if there is no pathogen to dump the granule contents onto during an allergic response?
contents will be dumped onto your tissues = causes inflammation
What is the main role of PolyIgR?
transports IgA and IgM from blood to tissues or lumen of tissues
What is FcRn?
neonatal receptor that helps IgG cross placental barrier
What is the 2nd signal needed for CTL activation?
CD28
What 2 genes does cytokine signaling of IL2 lead to the expression of?
Bcl-2 (pro-survival gene) | CD25 (IL2R)
What are the 2 ways in which CTLs can kill infected/tumor cells?
intrinsic pathway | extrinsic pathway
What is the intrinsic pathway of CTLs?
produce protein to insert into infected/tumor cell
What are the 2 key proteins in the intrinsic pathway of CTLs?
perforins | granzymes
What are perforins?
pore-forming protein
What are granzymes?
proteases that turn on caspase (apoptotic) molecules
What is the extrinsic pathway of CTLs?
engages the Fas/FasL CTL ligand with the FasR receptor on target cell = interaction activates caspase = activates apoptosis
How do CTLs insert apoptotic proteins into target cell?
perforin and granzyme = exocytosed »_space;> target cell endocytoses them »_space;> perforin makes a pore on endocytic vesicle to let granzymes out = activate caspase = induce apoptosis
What is the missing self model of NK cells?
NK cells recognize and kill infected/tumor cells by absence of MHC I
How do NK cells interact with normal cells?
normal cells have both NK activating ligand AND MHC I ligands
If a cell presents more MHC I than activating ligand, what does the NK cell do?
over-representation of MHC I will bind to more inhibitory receptors on NK cell = NK-cell inhibition
If a cell presents less/no MHC I and has more activating ligands, what does the NK cell do?
under-representation or no expression of MHC I = less binding of inhibitory receptor and more binding of activation receptor = NK cell activation = target cell dies
If a cell has an equal number of MHC I and activating ligand, what does the NK cell do?
nothing happens
What does “missing self” mean?
the loss of ability to express self-protein (ie: MHC I) on cell surface