antigen-antibody interactions

antigen-antibody interaction

is a bimolecular association similar to an enzyme-substrate interaction, with an important distinction: it does not lead to an irreversible chemical alteration

epitope of the antigen, variable-region of the antibody molecule

the association between an antibody and an antigen involves various noncovalent interactions between the ______________ and the __________________

hypervariable regions, complementarity-determining regions

The association between an antibody and an antigen involves various noncovalent interactions between the antigenic determinant, or epitope, of the antigen and the variable-region (VH/VL) domain of the antibody molecule, particularly the __________________________ or ______________________.

immunoassays

play vital roles in diagnosing diseases, monitoring the level of the humoral immune response, and identifying molecules of biological or medical interest

hydrogen bonds, ionic bonds, hydrophobic interactions, van der waals interactions

noncovalent interactions that form the basis of antigen-antibody binding (4):

large

because noncovalent interactions are individually weak (compared with a covalent bond), a ________ number of such interactions are required to form strong Ag-Ab interaction

1 multiple choice option

very short

each noncovalent interaction between Ag-Ab operates over a ___________ distance

2 multiple choice options

close fit

a strong Ag-Ab interaction depends on a very ___________ between the antigen and antibody

complementarity

close fits require a high degree of ___________ between antigen and antibody, a requirement that underlies the exquisite specificity that characterizes Ag-Ab interactions

affinity

the combined strength of the noncovalent interactions between a single antigen-binding site on an antibody and a single epitope

weakly; readily

low-affinity antibodies bind antigen ____________ and tend to dissociate _____________

tightly; longer

high-affinity antibodies bind antigen more ___________ and remain bound ______________

Ag + Ab <-k1/k-1-> Ag-Ab

the association between a binding site on an Ab with a monovalent Ag can be described by this equation

k1

the forward association rate constant

k2

the reverse dissociation rate constant

k1/k-1

the association constant Ka

Ka

a measure of affinity

Ka

the equilibrium constant that can be calculated from the ratio of the molar concentration of bound Ag-Ab complex to the molar concentrations of unbound antigen and antibody at equilibrium

Ka = Ag-Ab/(Ab)(Ag)

Because Ka is the equilibrium constant, it can be calculated from the ratio of the molar concentration of bound Ag-Ab complex to the molar concentrations of unbound antigen and antibody at equilibrium as:

small haptens

for __________, the forward rate constant can be extremely high

protein antigens

for larger __________, k1 is smaller

inversely proportional

the relationship between k1 and the size

close complementarity

in an aqueous environment, noncovalent interactions are extremely weak and depend upon _____________ of the shapes of antibody and antigen

Kd

the reciprocal of Ka

Ka

is a quantitative indicator of the stability of an Ag-Ab complex

inversely proportional

the relationship between Kd value and the stability of complexes

equilibrium dialysis

affinity constant Ka can be determined by ___________

equilibrium dialysis

this procedure uses a dialysis chamber containing two equal compartments separated by a semipermeable membrane

haptens, oligosaccharides, oligopeptides

suitable ligands in equilibrium analysis

difference in ligand concentration in two compartments

principle of equilibrium dialysis

antibody

in equilibrium dialysis, the total concentration of ligand will be greater in the compartment containing ____________

directly proportional

in equilibrium dialysis, the relationship between the affinity of the antibody and the amount of ligand bound

scatchard equation

equation to get the affinity of a complex

valency

the number of binding sites per antibody molecule

polyclonal

most antibody preparations are ______________

Ka

not a constant because a heterogeneous mixture of antibodies with a range of affinities is present

heterogeneous antibody

A Scatchard plot of ______________ yields a curved line whose slope is constantly changing, reflecting this antibody heterogeneity

true strength

the affinity at one binding site does not always reflect the _____________ of the Ab-Ag interaction

probability

When complex antigens containing multiple, repeating antigenic determinants are mixed with antibodies containing multiple binding sites, the interaction of an antibody molecule with an antigen molecule at one site will increase the ___________ of reaction between those two molecules at a second site

avidity

the strength of multiple interactions between a multivalent antibody and antigen

avidity

is a better measure of Ag-Ab complex's binding capacity within biological systems

low affinity

high avidity can compensate for ______________

IgM

has lower affinity than IgG

IgM

has higher avidity than IgG

cross-reactivity

occurs if two different antigens share an identical or very similar epitope

ABO blood-group antigens

an example of antigens where cross-reactivity is often observed

antibodies

in A and B blood-group antigens, an individual lacking one or both of these antigens will have serum _______________ to the missing antigen(s)

microbial antigens

The antibodies are induced not by exposure to red blood cell antigens but by exposure to cross-reacting ______________ present on common intestinal bacteria

microbial antigens

induce the formation of antibodies in individuals lacking the similar blood-group antigens on their red blood cells

blood-group antibodies

although elicited by microbial antigens, will cross-react with similar oligosaccharides on foreign red blood cells, providing the basis for blood typing tests and accounting for the necessity of compatible blood types during blood transfusions

anti-b

antibodies of type a individuals

anti-a

antibodies of type b individuals

neither

antibodies of type ab individuals

anti-a, anti-b

antibodies of type o individuals

a

antigens on rbcs of type a individuals

b

antigens on rbcs of type b individuals

a, b

antigens on rbcs of type ab individuals

neither

antigens on rbcs of type o individuals

Streptococcus pyogenes

example of bacterium that expresses cell-wall proteins called m antigens

vaccinia virus

an example of a vaccine that exhibits cross-reactivity

cross-reactivity

the basis of jenner's method of using vaccinia virus to induce immunity to smallpox

precipitins

antibodies that aggregate soluble antigens

precipitate

Antibody and soluble antigen interacting in aqueous solution form a lattice that eventually develops into a visible _____________

1-2 days

formation of the soluble Ag-Ab complex occurs within minutes, formation of the visible precipitate occurs more slowly and often takes __________ to reach completion

valency

formation of an Ag-Ab lattice depends on the _________ of both the antibody and antigen

bivalent

to form a lattice, the antibody must be ______________

bivalent, polyvalent

to form a lattice, the antigen must be either _____________ or ____________

monoclonal antibody

in this type of antibody, there is no precipitate formed

constant

a quantitative precipitation reaction can be performed by placing a ____________ amount of antibody in a series of tubes and adding increasing amounts of antigen to the tubes

precipitin curve

Plotting the amount of precipitate against increasing antigen concentrations yields a _____________

equivalence zone

excess of either antibody or antigen interferes with maximal precipitation, which occurs in the so-called __________________, within which the ratio of antibody to antigen is optimal

antibody excess, antigen excess

under conditions of ____________ or _______________, extensive lattices do not form and precipitation is inhibited

zone of antibody excess

zone in which precipitation is inhibited and antibody not bound to antigen can be detected in the supernatant

equivalence zone

a zone of maximal precipitation in which antibody and antigen form large insoluble complexes and neither antibody nor antigen can be detected in the supernatan

zone of antigen excess

zone in which precipitation is inhibited and antigen not bound to antibody can be detected in the supernatant

agar matrix

immune precipitates can form not only in solution but also in an ______________

line of precipitation

When antigen and antibody diffuse toward one another in agar, or when antibody is incorporated into the agar and antigen diffuses into the antibody-containing matrix, a visible ________________ will form

radial immunodiffusion, double immunodiffusion

2 immunodiffusion reactions that can be used to determine relative concentrations of antibodies or antigens, to compare antigens, or to determine the relative purity of an antigen preparation

mancini method

other name for radial immunodiffusion

ouchterlony method

other name for double immunodiffusion

semisolid medium

both immunodiffusion methods are carried out in a _______________ such as a gar

radial immunodiffusion

in this method, an antigen sample is placed in a well and allowed to diffuse into agar containing a suitable dilution of an antiserum

radial immunodiffusion

in this method, as the antigen diffuses into the agar, the region of equivalence is established and a ring of precipitation, a precipitin ring, forms around the well

precipitin ring

ring of precipitation

directly proportional

the relationship between the area of the precipitin ring and the concentration of antigen

standard curve

By comparing the area of the precipitin ring with a ___________ (obtained by measuring the precipitin areas of known concentrations of the antigen), the concentration of the antigen sample can be determined

double immunodiffusion

in this method, both antigen and antibody diffuse radially from wells toward each other, thereby establishing a concentration gradient; as equivalence is reached, a visible line of precipitation, a precipitin line, forms

radial immunodiffusion

in this method, the antigen diffuses

double immunodiffusion

in this method, both the antibody and the antigen diffuse

immunoelectrophoresis

in this method, the antigen mixture is first electrophoresed to separate its components by charge

immunoelectrophoresis

combines electrophoresis and double immunodiffusion

electrophoresis, double immunodiffusion

immunoelectrophoresis combines these two methods

immunoelectrophoresis

is used in clinical laboratories to detect the presence or absence of proteins in the serum

immunoelectrophoresis

This technique is useful in determining whether a patient produces abnormally low amounts of one or more isotypes, characteristic of certain immunodeficiency diseases

immunoelectrophoresis

It can also show whether a patient overproduces some serum protein, such as albumin, immunoglobulin, or transferrin

qualitative

immunoelectrophoresis is a strictly __________ technique that only detects relatively high antibody concentrations

immunoelectrophoresis

is a strictly qualitative technique that only detects relatively high antibody concentrations (greater than several hundred g/ml), its utility is limited to the detection of quantitative abnormalities only when the departure from normal is striking, as in immunodeficiency states and immunoproliferative disorder

rocket electrophoresis

electrophoresis that permits measurement of antigen levels

rocket electrophoresis

in this method, a negatively charged antigen is electrophoresed in a gel containing antibody; the precipitate formed between antigen and antibody has the shape of a rocket, the height of which is proportional to the concentration of antigen in the well

negatively charged

One limitation of rocket electrophoresis is the need for the antigen to be ______________ for electrophoretic movement within the agar matrix