Antibody Structure and Function Flashcards
what are antibodies
specifically induced serum glycoproteins which recognize antigens
where are antibody molecules found
- circulate in the blood
- present in body secretions
- found on the surface of B cells (act as antigen-spec receptors)
how can antibodies inactivate pathogens
-directly inactivate pathogens following interaction w/ relevant antigenic determinants that they express
what can antibodies stimulate
non-specific host effector mechanisms such as complement proteisn and cytotoxic cells
-can also act as opsonins
which end of antibodies recognize antigenic determinants (epitopes) on the antigen
amino terminal end of the molec contains the antigen binding site which recognizes epitopes
which end of ab binds various effector cells and molecules
carboxy terminal portion
what were the major bands that were revealed when serum proteins were separated into fractions
albumin
alpha
beta
gamma globulins
which fraction is the only one capable of passively transferring humoral immunity from an immunized donor to a naive recipient
gamma globulin fraction
known as passive immunization or vaccination
how are gamma globulin and albumin different
gamma is not a homogenous protein, it consists of many diff molec having the same basic structural features but diff aa sequences
what is the molecular weight of a typical gamma globulin
150,000 daltons
what make up the basic immunologic structure
2 identical heavy chains of 50,000
2 light chains of 25,000 daltons
what is papain
an enzyme that produces fragments of approx equal molec weight but of diff molec composition when digested with immunoglobulin
what are fab fragments
fragments that retain their ability to bind antigen after being liberated by papain digestion
“fragments w/ antigen binding activity)
what is an fc fragment
crystallizable fragment
what is pepsin
an enzyme when digusted liberates a single fragment of approx 100,000 daltons which exhibi antigen binding capability
why is f(ab)2 referred to as being bivalent
it can bind antigen at 2 sites
what is f(ab)2 held together by
disulfide bond
what do multiple myeloma tumor cells produce
a single homogeneous innunoglobulin w/ one aa sequence (confirming clonal selection theory)
patients with multiple myeloma secrete what
prodigious amounts homogeneous antibody, which facilitate the sequencing of the molec
what are immunogloblulin molec held together by
interchain disulfide bonds within each of the protein chains
non-covalent, ionic, and hydrophobic bonds
what are the 2 classes of light chaisn in humans
kappa and lambda
-each antibody molec has either kappa or lambda chains, not both
how many classes of heavy chains are there in humans
10
what part of the light and heavy chain is responsible for antigen recognition (fab portion)
amino terminal half of the light chain
amino terminal quarter of the heavy chain
where are the variable (V) regions located at
the end of the chain
-in the amino terminal
where are the C regions located at
close to the hinge
what are the hypervariable regions
-highly divergent stretched w/in the V regions
what form the antigen-binding cleft
hypervariable regions of apposed heavy and light chains of each Fab fragment
where is the hinged region, what does it do
in the heavy chains
affects the flexibility of movement of Fab portions
-in some it can allow both fab portions to bind antigen, rather than just 1, which increases the strength of ab attachment
where are the constant regions of immunoglobulin on the heavy and light chains
3/4 of the heavy chains from the carboxy end and similar half of the light chains
where are complx carbs located on the chains
heavy chains in the Fc region
what involves the rearrangement of the germinline DNA endocding the heavy chain
first steps in B cell development
what are the major classes of antibody isotypes
igG, A, M, E, D
“Gamed”
which isotypes can be subdivded into closely related subclasses “subtypes”
igA and igG
what creates the different isotpes
sequence of aa in the heavy chain make the difference
which is the first isotype that is released by plasma cells
igM
which is the most effective complement-activating antibody isotype, why
igM
=secreted form found in serum is a pentamer (consits of 5 igM monomers => 10 antigen binding sites
which isotypes are found on virgin B cells (havent seen antigen yet)
igM and igD
how do you form secreted igM
monomers are polymerized in the cell by a process requiring the production of a separate protein called the J chain, which links and stabilizes them
which is the first immunoglobulin produced during the immune response
igM
what is the primary functino of igD
rare found in serum
to act as a second antigen receptor
what is the major immunoglobulin class found in serum
igG
what is the role of igG
activates complement
act as B cell surface antigen-receptors on memory B cells (cells that are produced after initial antigen stimulation)
where is igA found
relatively low concentrations in the serum but is abundant in body fluids like intestinal and mucous secretions, saliva, tears, and colostrum
what ist he only isotype that can be transported across epithelial cell boundaries
igA
which isotype is critical for host defense againt organisms that cn invade the body
igA
which isotype binds to polymeric immunoglobulin receptors on the basolateral membranes of lacrimal acinar cells
igA
what does the secretory componene tsreve as
to protect igA from degradation by microbial proteases produced
ex ocular surface bacteria
what is immune repertoire
the established pool of immunoglobulin V regions that is present in an indiv
what are the 3 mech by which the immune system generates an enormous variety of diff V regions on immuno heavy and light chains
- multiple genes: large # of separte genes which encodes one V region domain
- somatic (genetic) mutation: V region mutates during B cell devleopment to produce diff genes in diff B cell clones
- somatic recombination: # of gene segments recombine to join the main part of the V regino gene. results in protein containing elements coded for by diff gene segments
what are the antimicrobial functions of secretory igA
- agglutination (clumps)
- preventino of microbial attachment
- inactivation of bacterial enzymes and toxins
- antibody-dependent cell mediated cytotoxicity
- opsinization (igA acts as opsonin)
which isotype are good at complement activation
which is not
igG and igM
igA is not good
how can antigens enter the body
- from the gut through M cells (delivers antigen directly to underlying immune cells)
- through more common enterocytes (ep cells taht line the gut)
who described monoclonal ab
georges kohler
cesar milstein
what are hybridomas
immortilized cells produced with monoclonal antibodies of pre-determined specificity
what are the applications of monoclonal antibody tech
- identificatino of phenotypic markers of cell types
- purified isolation of cell types with unique markers
- purification of antigens
- immunodiagnosis
- functional analysis of cell-surface and secreted molec
- immunotherapy and immunosuppresion
