Humoral Responses Flashcards
secreted antibodies bind to
- extracellular microbes
following binding of antibodies to extracellular microbes
- microbes are ingested by phagocytic cells
what enhanced the microbe-killing abilities of phagocytic cells
- helper T cells
function of helper T cells
- recruit leukocytes to destroy microbes
- strengthen epithelial barrier to expel microbes
when B cells engage polysaccharide or lipid antigen
- plasma cells secrete IgM only
when B cells engage protein antigen only
- requires assistance from CD4+ helper T cells for full response
B cells acting as antigen presenter cells for protein antigen
- ingest protein antigen
- degrade them
- display peptides bound to MHC II for recognition by helper T cells
how helper T cells activate B cells
- express cytokine and cell surface proteins
- work together to activate B cells
specificity of the antibodies secreted by B cells
- exactly like the antigen-binding specificity as the starting B cell receptor
- one B cell makes one antibody of one specificity to one epitope
using polysaccharides and lipids as antigen only
- stimulates synthesis of IgM
using protein antigens with help from helper T cells
- production of IgG, IgA, and IgE antibodies
isotype switching
- making different antibodies
- same specificity
affinity maturation
- helper T cells stimulate production of antibodies with higher affinity for the antigen
naive B cell has which antibodies on it surface
- IgM
- IgD
Do B cells need fragments or whole molecules for recognition?
- whole molecules
antibody molecules composed of
- two identical light chains
- two identical heavy chains
antigen binding fragment
- Fab region
what recognizes the Fc region
- macrophages
- neutrophils
- mast cells
- basophils
- eosinophils
- have Fc receptors
IgA found
- mucosal areas
- nose
- breathing passages
- digestive tract
- ears
- eyes
- vagina
IgA antibodies protect
- body surfaces exposed to outside foreign antigen
- mucosal immunity
IgG antibodies found
- in all body fluids
IgG antibodies compared to other antibodies
- most common antibody of all the antibodies in the body
- only antibody that can cross the placenta
IgG antibodies important in
- fighting bacterial and viral infections
- opsonization
- complement activation
- antibody-dependent cell mediated cytotoxicity
- neonatal immunity
- feedback inhibition of B cells
IgM antibodies compared to other antibodies
- they are the largest antibody
- pentamer
IgM antibodies found
- in blood and lymph
IgM antibodies importance
- first type of antibody made in response to an infection
- naive B cells antigen receptor
- complement activation
IgE antibodies found
- lungs
- skin
- mucous membranes
IgE antibody importance
- involved in allergic reactions (mast cell hypersensitivity)
- cause the body to react against foreign substances like pollen, fungus spores, and animal dander
- high in people with allergies
- defense against helminthic parasites
IgD antibodies found
- surface of newly matured B cells
which antibody is best with neutralization
- IgG
- IgA
which antibody is best for opsonization
- IgG1
which antibody is best for sensitization of mast cells
IgE
which antibody is best for complement activation
- IgM
- IgG3
which antibody can transport across epithelium
- IgA
which antibody can transport across the placenta
- IgG1
which antibody can diffuse into extravascular sites
- IgG
B cell maturation process
- stem cell
- Pro-B
- Pre-B
- immature B
- mature B
Ig expression of mature B
- membrane IgM and IgD
mature B cells are called
- follicular B cells
- found in lymph node and spleen follicles
marginal zone B cells found
- margins of the splenic follicles
marginal zone B cells develop
- from the same progenitors as do follicular B cells
B-1 lymphocytes found
- in lymphoid organs
- peritoneal cavity
B-1 lymphocyte development
- may develop early
- may develop from different precursors
follicular B cells with protein antigen + helper T cells
- isotope switched
- high affinity antibodies
- long lived plasma cells
marginal zone B cells with lipid, polysaccharides
- mainly IgM
- short lived plasma cells
B-1 cells with lipid, polysaccharides
- mainly IgM
- short lived plasma cells
primary response lag after immunization
- 5-10 days
secondary response lag after immunization
- 1-3 days
primary response peak response
- smaller
secondary response peak response
- larger
primary response antibody isotype
- IgM>IgG
secondary response antibody isotype
- increase in IgG
- sometimes IgA or IgE
primary response antibody affinity
- lower average affinity
- more variable
secondary response antibody affinity
- higher average affinity
- affinity maturation
C3d
- breakdown product of C3b
- binds B cells through complement receptor type 2
- CR2 or CD21
engagement of CR2 by C3d
- enhances antigen-dependent activation responses of B cells
B cells and toll-like receptors
- B cells express numerous toll-like receptors
TLR engagement on B cell by microbial products
- triggers activating signals that work in concert with signals from B cell receptor
Expression of TLRs in B cells
- provides a cell-intrinsic mechanism for innate signals regulating adaptive immune responses
functional consequences of B cell activation by antigen
- entry into cell cycle: mitosis
- increased expression of cytokine receptors
- low-level IgM secretion
significance of entry into cell cycle, mitosis
- clonal expansion
significance of increased expression of cytokine receptors
- ability to respond to cytokines produced by helper T cells
significance of migration out of lymphoid follicles
- interaction with helper T cells
significance of secretion of low levels of IgM
- early phase of humoral immune response
activation of CD4 helper T cells and B cells
- independently activated by a protein antigen
- in different regions of a lymph node
CD4s activated where in lymph node
- extra follicular
B cells activated where in lymph node
- follicle
B cells present antigen on
- MHC II
activated helper cells express
- CD40 ligand
- SUPER IMPORTANT FOR ACTIVATING B cells
activated helper cells secrete
- cytokines
- act on B cells to initiate proliferation and differentiation to plasma cells
After B and helper T cells are activated, where do they go
- migrate back to follicle
- B cells proliferate
what forms while B cells proliferate
- a germinal center
proliferating germinal center B cells undergo
- somatic mutation of antibody gene variable regions
- Ig heavy-chain isotype switching
what is selected in the germinal center
- high affinity B cells
- results in production of high affinity antibodies
high affinity antibodies leads to generation of
- long-lived plasma cells
- memory B cells
where do long-lived plasma cells migrate to
- bone marrow
- where they secrete IgG
what cytokine helps with class switching to IgG - secreted by
- interferon gamma
- Th1
what cytokine helps with class switching to IgE - secreted by
- IL-4
- Th2
what cytokine helps with class switching to IgA - secreted by
- TGF-B
- BAFF
how to get affinity maturation
- have already undergone somatic mutation and have different affinities for antigen
- B cells with high affinity membrane Ig bind antigen on follicular dendritic cells
- present that antigen to helper T cells
- those survive
