Exam 3: Humoral Immune I Flashcards
Passive humoral immune response
artificial
natural
artificial - immunoglobulins
natural - transplacental, colostrum, egg
Active humoral immune response
artificial
natural
artificial - vaccination
natural - diseases
B lymphocyte antigen receptors
characteristics (4)
200,000 - 500,000 BCRs on cell membrane
antibodies are soluble BCRs
all BCRs are antibodies
BCR and antibodies belong to superfamily of proteins: immunoglobulins
BCR strucutre
2 light chains and 2 heavy chains
what attaches light chain to heavy chain
light chain protein attached to heavy chain protein by disulfide bonds
what attaches heavy chains together
disulfide bonds attach heavy chains together
how many constant domains and variable domains in heavy and light chains
Light chain: 1 constant domain, 1 variable domain
Heavy chain: 3-4 constant domains, 1 variable domain
Fab and Fc
Fab is fragment antigen-binding
part of BCR above hinge region
Fc is fragment crystallization
part of BCR below hinge region
what is hinge region
part of heavy chain where disulfide bond is that connects the heavy chain
what enzyme causes fragmentation of antibody
papain or pepsin
breaks antibody into Fab and Fc
which fragment is more antigenic
Fc - because bigger and more constant
which fragment is used to avoid immune reaction in a receptor animal
Fab - smaller, has variable portions
Light chain domains
constant domain C1 (CL)
variable domain V1 (VL)
Light kappa chain (k)
Light lambda chain (λ)
Both light chains are the same, either both lambda or both kappa
Heavy chain domains
4-5 chains domain
always 1 variable, domain 3-4 constant domains
variable domain VH
Constant domain CH
five different types of heavy chain domains
alpha (α) -- IgA
gamma (γ) -- IgG
delta (δ) -- IgD
epsilon (ε) -- IgE
mu (μ) -- IgM
both heavy chains are the same - both alpha, both gamma, both delta, both epsilon, or both mu
variable domain - hypervariable regions
AKA complementary determining regions (CDR)
3 regions (CDR1, CDR2, CDR3)
highly variable areas of variable domain
variable domain - framework regions
between hypervariable regions
relatively constant areas of variable domain
epitope-variable domain interaction
complementary determining regions come together with epitope
when epitope not there the space is called a paratope
like a lock and key
key is the epitope, lock is the receptor
need correct epitope for a specific receptor
what part of the antibody does the antigen bind to
the variable domain
differences between different types of heavy chains
alpha, gamma, and delta heavy chains – 3 constant domains –> CH1, CH2, CH3
mu and epsilon heavy chains – 4 constant domains –> CH1, CH2, CH3, and CH4
what part of antibody is the antigen binding site
VH + VL
what part of antibody stabilizes the antigen binding site
CH1 + CL
Why do IgG and IgM antibodies have complement activating regions
IgG and IgM can activate the classical pathway of the complement system
Which part of the antibody can move
Fab part can move in order to have better interaction with the antigen
both Fab parts can move
what “CD” is present on all B cells and not present on T cells
CD 79
if want to find only B cells can use antibody against CD 79
CD 21 and CD 19 interaction
CD 21 - complement receptor for C3d
CD 19 - signaling component
CD21 binds to C3d
Signaling through CD19, it generates a potent costimulatory signal to enhance B cell responses
B cell crosslinking
Activates B cells
Triggers cell division, differentiation, and immunoglobulin synthesis
both NF-kB and NF-AT are involved in B cell signal transduction
what must happen for B cell to respond to antigen
B cell must be stimulated by antigen
B cell must receive co-stimulation from T helper cells and their cytokines
what do B cells differentiate into
Plasma cells that produce antibodies
or memory cells
what do memory cells do
memory cells produce primary immune response and are APC in secondary immune response
what does Th2 promote
humoral immune response
IL - 4 (3 things)
Increased growth and differentiation of B cells
Increased expression of MHC II
Induces Ig class switching
IL-5 (4 things)
B cell differentiation into plasma cells
Stimulates IgM and IgG production
IL-5 + IL-4 induced IgE production
Selectively stimulates IgA production
IL-6 (3 things)
Needed for final differentiation of B cells into plasma cells
IL-6 + IL-5 promotes IgA production
IL-6 + IL-1 promotes IgM production
IL-13 (2 things)
Similar to IL-4
Required for optimal induction of IgE
what happens during primary immune resposne
antigen is processed by a dendritic cells and presented to the helper T cell
what happens during the secondary immune response
the B cell itself can act as an APC
Co-stimulators (CD154, CD28) engage serially to trigger IL-4 secretion by the T cell and IL-4R production by the B cell
CD154 and CD 40 interaction
CD 154 on T cell
CD40 on B cell –> proliferation, Ig production, Ig class switching
CD40 on dendritic cell –> antigen presentation, cytokine production, cell survival
Cd40 on macrophage –> cytokine production, activation
what happens when PAMPs bind to TLR on B cell (5)
B cell activation and proliferation
No participation of helper T cells
Only IgM response
No memory cells
No immunoglobulin class switching
what kind of antigen can BCRs bind to
free soluble antigens
recognizes “native” epitopes as opposed to processed epitopes
antigen + BCR and presence of helper T cell causes (3)
increased IgM BCR
Increased MCH II
increased IL-4, IL-5, IL-6, TNF-a, TGF-B receptors
Ig class switching
IL-4 –> IgG, IgE
IFN- γ –> IgG
TGF-B –> IgA
Il-5, IL-6 –> IgG, IgM, IgA
plasma cells
short lived population - 1 or 2 weeks
spleen and lymph nodes after immunization
long lived population - months to years
accumulate in bone marrow
memory cells
long lived resting memory cells
survival do not depend on antigen contact
large and dividing memory cells
survival depends on antigen contact
memory cells survival in humans - 60 years
germinal center
antigen derived cell proliferation
somatic hypermutation
positive and negative B cell selection
stimulated B cells + Th cells migrate to germinal center around 6 days after response begins
antibodies fight against?
viruses
protozoa
bacteria
toxins
local and general specific protection by antibodies
milk
body surfaces
blood circulation
antibodies - multiple immunoglobulin classes
IgM IgG IgA IgE IgD
serum concentration of immunoglobulin classes
IgG - highest IgM IgA IgD IgE - lowest
where does IgA have a high concentration
saliva, milk, GI fluids
IgG (4)
plasma cells in spleen, lymph nodes, bone marrow
important in inflammation
agglutination, opsonization
activate classical complement pathway
IgM (5)
plasma cells in secondary lymphoid organs
complement activation site is on CH4
major Ig produced in primary immune response
opsonization, virus neutralization, agglutination
not very important in inflammation
IgA (3)
plasma cells in body surfaces: intestines, respiratory tract, urinary system, skin, mammary gland
transported through intestinal epithelial cells into external secretions
major Ig in external secretions of non ruminants
IgE (6)
Produced by plasma cells located under body surfaces
IgE attached to FceRI on mast cells and basophils
IgE + antigen –> inflammation –> enhances local defense
release inflammatory molecules from mast cells
immunity against parasites
shortest half life of all Igs
IgD (4)
not present in cats, chickens, rabbits
IgD mainly attached to B cells
some circulating IgD binds to basophils = IL-4, IL-1, cathelicidins, and B cell activator factor
mediated link between innate and adaptive immune response
what do all cattle possess
a complete set of classes and sub classes (isotypes)
within a population what do individual cattle possess
different allotypes
Example: IgG2(A1) or IgG2(A2)
what does each individual animal have
a very large number of different idiotypes
exons vs introns
Intron - don’t code for protein and are deleted from gene
Exon - each exon codes for a different component of the constant domain of the heavy chain
example: exon 1 may code for CH1 while exon 2 codes for CH2 and exon 3 codes for CH3
a different set of genes codes for the variable domain
Antibody production
V(D)J recombination = antigen binding site
variable part
V = variable gene
D = diversity gene
J = joining gene
Antigen activation of B cells = switch in the class of antibody –> constant part
class switching
genes that code for different Ig classes are deleted and the variable gene and correct Ig class gene are joined
Example: want IgA
V – Cmu – Cdelta – Cgamma – Cepsilon – Calpha
Delete Cmu, Cdelta, Cgamma, Cepsilon to get
V – – – – – Calpha
join these to make IgA –> V–Calpha
IgM serving as BCRs have a choice as to which C terminal domain they will use
Membrane bound form uses hydrophobic transmembrane domain (CmuM)
Secreted form deletes this sequence and uses CmuS gene
difference between the 2 forms is determined by RNA splicing following transcription
antibody levels at first and second doses of antigen
first dose - IgM is higher
second dose - IgG is higher
at second dose total Ig is much higher than at first dose
primary vs secondary immune response - levels of Ig
Primary immune response – IgM
Secondary immune response – IgG
secondary immune response - antigen is
recognized by memory cells
Which Ig has the most subclasses
IgG has the most subclasses (all species in chart)
IgA has a few subclasses in some species (sheep, mice, humans)
IgM has 2 subclasses in humans
IgE has 2 subclasses in dogs (might have 2 in cats)
Cats do not have IgD (or it hasn’t been found yet?)
What are each of the Ig classes involved in
**IgM and IgG activate classical complement pathway
IgA1 activate lectin complement pathway
**IgG - placental transfer
IgG1, IgG3, IgG4, IgA1, IgA2, IgE - binding to macrophages and other phagocytes
**IgE - high affinity binding to mast cells and basophils
IgE - lowest serum content
Where can each Ig be found
IgA - provides immunity in mucosa
including urinary, reproductive tract, gut,
respiratory
IgE - skin and mucosa (linings?)
IgG - provides systemic protection
IgM and IgG - blood circulation
Can’t find IgM in other parts of body because it is too big
