Humoral Immunity I (Lecture 3) Flashcards
Effector Functions of Antibodies
Interactions with Accessory Molecules
LETS RIDE
The Complement System
3 types of events that result from activation of complement cascade, can be activated via of ____ different pathways
only talking about one pathway
three
The Complement System
- Plays a role in both ____ and ____ immunity.
- Involves a large number of ____ proteins and cell membrane receptors including the nine complement components that are designated C1 through C9.
- C1 through C9 are ____ proteins normally found in an ____ state.
- Activation of the system involves the sequential ____ of the individual components to generate proteolytic fragments that act on the subsequent component in the cascade.
- The products of this enzymatic cascade become ____ bound to the surface of a ____ or an ____ molecule attached to the microbe.
innate
acquired (humoral)
soluble
plasma
inactive
cleavage
covalently
microbe
antibody
The Complement System
- The system is tightly ____ by a number of molecules to prevent uncontrolled complement activation including proteins that are found on normal ____ but absent from ____ surfaces.
- There are three major pathways of complement activation:
- the ____ pathway,
- the ____ pathway,
- the ____ pathway.
regulated
host cells
microbial
classical
alternative
lectin
The Complement System
even though ____ is different in each scenario, they all ultimately lead to the same three events: recruitment of ____, ____ of pathogens and the killing of the actual ____
be most familiar with is the classical pathway, bc it requires the presence of ____ molecules in order for it to be activated
activation
inflammatory
opsonization
pathogens
antibody
The Complement System
complement activated via alternative or lectin mediated pathway > acting as a form of ____ immunity, certain bacterial molecules that can bind to certain components of the pathway and activate it in the absence of ____ (____ is an example and ____ that are on surface of microbes that have capacity to activate the pathway)
innate
antibody
LPS
lectins
The Classical Pathway
The Classical Pathway
1. The classical pathway can be activated by the binding of ____ to the Fc regions of ____ and ____ when the antibodies are bound to antigen (the surface of a microbe or as part of an immune complex).
(1) binding of IgG or IgM to surface of microbe > (2) Ab molecules can then interact with the first component of the cascade: C1; each arm is capable of interacting with Fc portion of IgM pentamer, or two IgG molecules (a single IgG will ____ activate the process)
there is an alteration in the conformation of the C1 molecule > enzymatic activity on ____
C1
IgG
IgM
not
C4
The Classical Pathway
2. This event induces a conformational change in C1 which allows it to act on the next component, ____, cleaving it into two fragments.
C4 cleaved into two fragments: ____ and ____
C4A acts on next component: ____ > C2 acts on ____, follow the numbers below
- The cascade subsequently proceeds in the sequence of C2, C3, C5, C6, C7, C8, and C9.
C4 C4A C4B C2 C3
The Classical Pathway
4. Individual proteolytic fragments are biologically active:
- C3a, C4a and C5a are potent ____ of inflammation.
- C3b acts as ____ via binding to specific receptors
on the surfaces of certain types of phagocytic cells.
C3A, C4A, C5A > enhance inflammation, induce changes in structure of endothelial cells thereby increasing ____, the contents of blood in that environment will enter the EC space; can also act as ____ > bring WBC into the space where the complement has been activated
C3B > act as an opsonin > mediates opsonization; bacterial cell, C3B fragments accumulating on surface of cell, in addition to innate and Fc receptors, ____ also have complement receptors on surfaces; C3B provides the highest interaction bt phagocytic cell and bacterial cell > highest level of ____ at which microbe can be phagocytosed and eliminated
opsonization involved antibodies, complements, Fc receptors, etc.
inducers
opsonin
vascular permeability
chemoattractant
macrophages
efficiency
The Classical Pathway
5. The terminal complement proteins (C5, C6, C7, C8 and C9) polymerize to form the ____. This generates ____ in the plasma membrane of the cell on which the cascade was activated that can lead to ____.
release of substances from cells can have a ____ effect on your own tissue; complement rids cells, but can also contribute to ____ because of release of molecules from bacterial cells
there is often ____ damage via this pathway
membrane-attack complex
pores
osmotic lysis
deletrious
tissue damage
collateral
The Complement System
presence of IgG, IgM to ____
C1 > ____
generation of cleavage fragments recruiting cells (C3A)
C3B involved in ____
and then generation of the membrane attack complex > pores > lysis
important in immunity against pathogens
what happens first? phagocytosis or complement pore? if not phagotosed via C3B, the cell will be eliminated via one pathway or another
C1
C4
opsoninization
Functions of Complement
- ____ of microbe
- recruitment and activation of ____ by C5A, C3A
- destruction of ____ by leukocytes
- ____ of microbe
important against ____ but not effective against something within your ____
phagocytosis
leukocytes
microbes
osmotic lysis
extracellular pathogens
cells
Maternal Transfer of Antibody (The “Good” Side)
In utero, maternal ____ is passed across the placenta via FcRn. After birth, maternal ____ and ____ can be passed via breast milk.
maternal IgG passed against ____ and into fetal circulation; continues all the way into birth and then disappears in ____ months
this antibody acts as an initial form of ____ immunity for the newborn infant;
begin producing ____ during utero, the only source is what has been passaged from maternal circulation
this antibody is not being reproduced, passed from mother to the infant > at 9 mo: producing only IgG and IgA; mediated via another FcRn (neonatal Fc receptor) > expressed in synctiotrophoblast cells
IgG taken up via Rm ____ > in endosome interacts with the receptor, protects from degradation and transfers it into fetal circulation
provides neonate with a source of IgG molecules; after birth, in mice, IgG and IgA can be transferred to newborn via breatmilk; but in humans ____ is transferred over
the secretory IgA that is taken up, is not taken into circulation, will only act against pathogens found within the ____ (exposed to often during first few months of birth; can survive without, however)
IgG IgG IgA synctiotrophoblast 9
adaptive
IgM
endocytosis
secretory IgA
GI tract
Maternal Transfer of Antibody (The “Bad” Side)
if mother has autoimmune disease involving IgG molecules > ____ DISEASE (____ antibodies); these antibodies can cross and enter the fetal circulation, and the infant can be born with grave’s disease
not a lifetime problem, as decay of maternal antibody takes place, the baby will recover (over ____ months the baby will ultimately recover)
Graves
anti-TSHR
9
Relative Role of Antibody Classes in Antimicrobial Immunity
❖ Now put this into context of the different kinds of pathogens- extracellular (EC) and intracellular (IC)
❖ Most antibody-mediated approaches are for ____
❖ If pathogen gets into cell, hard for antibodies to get at it
❖ Cell-mediated approaches are more for ____
extracellular pathogens
intracellular pathogens
Relative Role of Antibody Classes in Antimicrobial Immunity
antibody mediated immunity is important; in the case of influenza > can enter the mucosa > ____ is a mucosal antibody
once viruses are within our cells > evading humoral detection > ____ forms become important
IgA
cell-mediated
for bacteria; ____ is more important, cell-mediate immunity not as important
organisms on top are ____ pathogens; bottom of the list: spend most of time within cells
antibody-mediated
extracellular
Humoral Immunity
- B Cell Biology
Let’s talk about the cells responsible for producing antibodies
YA
Lymphocyte Differentiation
hematopoietic SC will differentiate into a ____ > can differentiate into NK cells, B cells, T cells
when lymphoid progenitor cells instructed to form B cells, all of this occurs within the ____ (when they differentiate into mature B lymphocytes)
common lymphoid progenitor cell
bone marrow
Cell Surface Markers
cannot differentiate between B and T cells ____
microscopically/morphologically
CD (Cluster of Differentiation) Molecules
Cell surface molecules expressed on
various types of immune cells:
• To date, approximately ____ different CD
molecules have been identified.
• Many have important functional roles in
immune reactions.
• They can be used as ____ markers
to differentiate between distinct types of cells (cell surface markers).
250
phenotypic
CD Molecules
____ on b cells, ____ on b cells
____, ____, ____ on t cells
____ - found on surface of NK cells; mediating ADCC
CD19
CD21
CD3
CD4
CD8
CD16
Cell Surface Markers
❖ Many companies cell antibodies against these cell surface molecules like CD3, 4, 8, 16, 19, 21
❖ Can take sample of ____ cells and incubate them with antibody molecules (often conjugated to fluorescent molecule)
❖ Mixture of ____ and ____ positive T cells
❖ Antibody against CD4 will bind to CD4 will bind to left, antibodies
against CD4 and CD8 will bind to middle, antibodies against CD8 will bind to right
human
CD4
CD8
Flow Cytometry
counts the number of cells that exerts certain ____
cells that fluoresce both = ____ color
allows you determine numbers of different subsets of immune cells
can purify diff ____ of cells based on cell surface markers, and add them back in to determine which are required for immunoloigc activites
fluorescence
orange
populations
B Cell Differentiation
For most antigens, B cell activation necessitates binding of the ____ to the cell’s antigen receptor and interaction between the B cell and a ____ cell.
This requires ____ contact between the cells and expression of membrane and secreted molecules (____) by the T cell that bind to receptors on the B cell.
cell’s antigen receptor = ____ molecule (for B cells)
interaction between B cell and T cells; they have ____ for one another
____ signals required for B cell activation in context of most types of antigens
antigen
T
physical
(cytokines)
antibody
ligands
two
B Cell Differentiation
For most antigens, B cell activation is a ____-step process initiated by binding of antigen to the B cell antigen receptor (antibody).
B cell has CD19, CD21 on surface > not involved in ____ process
molecules that are involved = membrane bound antibody molecules; encoded within the ____
first thing that has to happen; Ab on cell surface must engage an interaction with unique epitopes on antigen molecule; requires crosslinking of ____ Ab molecules
antigens that require this two-step process = ____ dependent antigens; cells derived from thymus are important are T cells
once B cell interacts with ____ cell > interaction of green box > second signal that leads to activation
two
inactivation
MHC
multiple
thymus
helper T
B Cell Differentiation
Binding of antigen to membrane immunoglobulin results in the delivery of biochemical signals that initiate the activation process.
amplification signals following engagement of receptor
ultimately results in ____; enhance expression of ____ encoding proteins that are involved in activity of B cell
TF
genes
B cell Differentiation
circulating throughout blood = ____ cells (never exposed to antigen before)
on surfaces > large # of Ab molecules; resting B cells express ____ and ____ on cell surface*** (unique characteristic of resting phase of mature B cell); the antibodies all have the same antigen specificity, they’re all ____
enter circulation, between blood and lymphatics; constantly through secondary lymphoid, looking for antigen
if they don’t bump into antigen, after a couple of days: ____; its to their advantage to encounter the antigen; then activated via interaction with T cell
begin to proliferate > give rise to genetically ____ daughter cells (expressing the same antigen receptor); T cells also secrete cytokines that tell B cells to stop producing ____ and produce others > ____; absent of help > become ____ cells (secrete ____ pentamer) (thymus independent antigens)
under influence of cytokines > plasma cells secreting ____, or ____, or ____; also results in generation of memory of cells
vaccine induces ____; some into IgM, IgG plasma cells, and memory cells (long lifespan) > memory responsible for large amounts of antibodies produced (secondary immune response)
resting B
IgD
IgM
identical
apoptosis identical IgD/IgM isotype switching plasma IgM
IgE
IgG
IgA (secretory)
clonal expansion
B Cell Differentiation cont.
❖ In addition to making plasma cells, this also generates memory cells that act
during second exposure to same antigen
o Vaccines are trying to induce this
o Plasma cells have ____ life span; memory cells have ____ life span
o Memory cells produce rapid secondary immune response within a couple of hours upon second exposure
❖ Also, note that proteins are ____ antigens
o This may be why they’re such ____ antigens
short
long
T-dependent
potent
How Is The Antigen Specificity Of A B Cell Determined?
side chain hypothesis; antigen that tells the cell what Ab to produce
selective (clonal selection) hypothesis: each B cell is ____, only has one type of antigen receptor on surface; antigen has nothing to do with determining specificity of B cell; close to original inference, except he thought that cell can express multiple receptors
monospecfic
The Clonal Selection Hypothesis
Antigen-Independent Stage of B Cell Differentiation
❖ In bone marrow, events give rise to resting B cells that express IgM and IgD on surface, all ____ of antigens
❖ We have monospecific cells being generated all the time with thousands of copies of receptor on surface
independent
The Clonal Selection Hypothesis
Antigen-Dependent Stage of B Cell Differenttiation
❖ Clonal Selection Hypothesis argues that cells in peripheral circulation, especially secondary lymphoid organs, are exposed to antigens
❖ Antigen that binds to cell
with appropriate receptor will provide signal 1
❖ This usually occurs in
conjunction with activation by T cells, signal 2
❖ Within clone of cells, some
differentiate into ____ cells and others differentiate into ____ cells that act in secondary, tertiary responses
❖ This is the accepted model
today
❖ People who proposed this
got a Nobel for coming up with better hypothesis than Erlisch in 1810 or 1820
plasma
memory B
The Clonal Selection Hypothesis
❖ Looking at diagram on right
❖ On top is IgM and IgD positive ____
❖ With antigen and T cell help, becomes ____
❖ T-cell derived cytokines instruct clones which ____ of antibody they will produce
❖ Not every microbe and body compartment is dealt with effectively with the same antibody
____
o Respiratory problems best dealt with ____
o If peripheral circulation problems, should make____
❖ So T cells ____ response and fine tune it to make appropriate type of antibody for
infection in body compartment
resting B cell activated B cell class response secretory IgA IgG quarterback
B Cell Differentiation
interaction bt mature B cell that has engaged antigen; receiving secondary signals from T cell
gives rise to genetically ____ daughter cells; under influence of cytokines will give rise to different ____ cells and ____
memory cells do not go through the ____ signalling (T-independent activation); certain antigens have charactristics that directly activate a B cell
identical
class switching
plasma
two-step
T-Dependent Versus T-Independent Antigens
t-independent: extremely repetitive types of structures > lipids, carbohydrates > activate b cells directly > only Ab that the b cells produce > ____ (does not have diverse capabilities that IgG has); in terms of protective function > you want ____; thymus indepedent > response is not ____ enough in protecting from infection, however, gets adaptive immune response ____
IgM
thymus-independent
potent
started
B Cell Differentiation
first response we see are production of ____ molecules; once interaction of B cells and T cells > production of ____ molecules (induce ____) > antibody molecules that have more diveristy function
as antigen diminishes, these antigens fall off; but a production of ____ cells have been produced
second time exposed > you have preformed population of cells that can recognize antigen (still ____ T cell help) > doesn’t take as long for it to happen, and predominantnly the class of antibody one sees is ____, the response slowly falls off
IgM
IgG
class switching
memory
require
IgG
