Acquired Immunity-Antibodies Flashcards
What type of cells secrete antibodies?
B cells
only cells in the body that are capable of making antibodies or immunoglobulins
What neutralizes toxins?
Antibodies bind to and neutralize toxins
antibodies neutralize toxins
toxin-antitoxin antibody complex cannot bind to target cells
What inactivates/prevent adherence and infections?
Antibodies bind to ectracellular bacteria and viral particle and inactivate/prevent adherence and infection
antigen:antibody complex is recognized by macrophages, internalized and eventually degraded.
Coating of antigen by antibody
opsonization
Antigen:Antibody complex can activate
complement system, which destroy antigen by lysis
antibodies bind to aged and damaged cells. macrophages have Fc receptors which phagocytose antibody-coated damaged cell and aid in clearance of old cells to keep the cell numbers in body optimum
Pathological role of antibodes
when B cells become tumorigenic, cancer results(myeloma)
antibodies against self antigens (autoantibodies) destroy self tissues (autoimmune disease)
antibodies provoke exaggerated/inappropriate response
Myeloma
plasma cell tumors
arise from single precursor cell or clone so secrete homogenous immunoglobulins of any class called myeloma proteins
Autoantibodies against red blood cells
bind to RBC and destroy them through complement-mediated damage or opsonization (facilitate phagocytes to engulf better) antibodies
Autoantibodies against synovial membrane and joint tissue
(rheumatoid factor) induce arthritis
Type 1 hypersensitivity
IgE and eosinophils
IgE
mediated allergic response
Primary lymphoid organs
development occurs-no antigen interaction
secondary lymphoidorgans
no further development of lymphocytes-site of antigen interactions
B cell development and differentiation
stem cell-Pre B cell (cytoplasmic mu chain)-immature B cell (membrane bound IgM and IgD)-mature B cell-memory cell or plasma cell (immunoglobulin secretion)
B cells have dual functions
secrete antibody (or immunoglobulin) production
antigen processing and presentation
antibodies play a critical role in defending against extracellular pathogen
antibodies cannot penetrate inside a cell, therefore not effective against intracellular pathogens
Antibodies exist in two forms
secretory and membrane bound (Surface)
secretory
detected in fluids such as serum, peritoneal cavity, mucosal fluids (humors) etc
(antibodies or immunoglobulins) found in body fluids (humors)
membrane bound (surface)
important for specific binding to antigens
on B cell surface as B cell receptor (BCR)
Secretory/free form of antibody
is found in the blood and body fluids as immunoglobulin. they neutralize antigen and assist in their removal
antibodies recognize free antigens( do not require combination with <HC unlike T cells)
antibodies are specific: bind speficially to antigen which induce antibody production
cannot penetrate the cell
Antibody structure
they are glycoproteins made of 4 polypeptide chains
have a flexible y shaped structure
Antibodies recognize shape of antigen
shapes of antigen and CDR(complementary determining regions of antibody)
each V region is folded in such a way that 3 CDRs come into contact with the antigen-creates a unique seat for antigen to sit
Fc site
for complement binding
Fc binds to
Fc receptors on cell surface
Antibody or Immunoglobulin classes or Isotypes
based on heavy chain characteristics, antibodies are divided into 5 classes
IgM-mu
IgG-gamma
IgA-alpha
IgE-epsilon
IgD-delta
IgM
first antibody to appear in circulation (predominant in primary antibody response
largest in size
membrane bound form is a monomer, secretory form is a pentamer
has a J chain
second highest in serum immunoglobulin level
IgM function
agglutinate antigen
Neutralize antigen
IgG
most abundant
monomer
smallest
can cross placenta in some species (primates and small percent in dogs and cats)
can move out of the blood stream and is found in tissue, blood vessels and other secretions
IgG function
Agglutinate antigen
neutralize antigen
important in inflammation
IgA
Has a secretory component (sigA) which allows IgA to appear in secretions and protected from digestion by proteases
prevents adherence of pathogen and antigen in general to mucosal surface and agglutinates
tends to be synthesized under intestinal, respiratory, reproductive and other mucosal surfaces
survive in harsh environment
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IgE
monomer
heavier than IgG
bound to mast cells and basophils (tissue and blood respectively) through a receptor Fc
Important in allergic reaction
IgD
monomer
similar to IgG
BCR bound only
secretion-negligible
found in human, rats and mice
Reasons to class switch
IgM to IgG (IgG is the only antibody which can penetrate placenta and blood vessels)
IgM to IgA (IgA is the only antibody that survive in mucosal sites that is enzyme rich and acidic)
IgM to IgE (IgE induces allergic type 1 hypersensitivity reaction)
Class switch-antibody retains specificity
during an antibody response, class switch, occurs in standard sequence
as immune response progrsses, B cells switches in presence of Th1 or Th2 cytokines and co-stimulatory molecules to one of the major secretory class
Fab does not change during class switch
B cell receptor (BCR) recombination
BCR determines the specificity of B cells
BCR binding to salmonella antigen is different than BCR binding to E.Coli
All B cells express
B cell receptors (binds specifically to antigen)
CD19 (binds to C3d-decrease the threshold for B cell receptor signaling pathways)
CD40(receptor for CD40L (or CD154) on activated T cells)
Th2 cytokines act on B cells
Th2- cells secrete cytokines that initiate B cell activation and differentiation
IL-4 induces class switch (IgM-IgE) enhances MHC class II and Fc receptor expression
IL-5 acts on activated B cells to differentiate into plasma cells (antibody secreting cells, not present in plasma)
Il-13 similar function as IL-4
IL-6 final differentiation of activated B cells into plasma cells
Summary-B cells surface markers
B cell receptor (immunoglobulin/antibody-membrane bound)
CD19 complex binds with complement C3d
CD40-binds to CD40L on T cells
CD68 binds with CD28 on T cells
MHC class I and MHC class II antigen processing and presentation
Th2 cytokine receptors such as IL-4R
