Immunology & Serology - Lecture - 7 - Antigen-Antibody Reactions - Part 1 - Complete

True

True or False

The combination of specific antigens with specific antibodies plays a very important role in the laboratory diagnosis, mainly in diagnosing many different diseases.

Hence, immunoassays have been developed to really detect either antigen or antibody and then vary from easily performed manual test to highly complex automated assays

Precipitation, Agglutination

Many assays are based on these principles

Precipitation, Agglutination, Complement Activation

Types of interactions in the immune system that are involved in defending the body against pathogens.

Precipitation

This interaction occurs when soluble antigens and antibodies form a precipitate

Agglutination

This interaction happens when particulate antigens (e.g., bacteria) aggregate due to antibody binding

Complement Activation

This interaction occurs when antigen-antibody complexes can activate the complement system, leading to the destruction of pathogens.

Precipitation

An example of this interaction are toxins binding to antibodies forming a visible insoluble precipitate/complex

Agglutination

In this immune system interaction, clumping helps phagocytes to efficiently engulf and destroy multiple pathogens at once

Multivalent antigens

This type of antigen according to valency, have multiple antigenic determinants (epitopes)

Multivalent antigens

This type of antigen according to valency, can form cross-linked complexes with antibodies

Multivalent antigens

This type of antigen according to valency, its cross-linking complexes with antibodies is necessary for precipitation, agglutination, and complement activation

Univalent antigens

This type of antigen according to valency, have a single determinant (epitope)

Univalent antigens

This type of antigen according to valency, do not cross-link

Univalent antigens

In this type of antigen according to valency, interaction with such antigens typically does not result in precipitation or agglutination.

Univalent antigens

This type of antigen according to valency, have 1 binding site for antibodies forming a single antigen-antibody complex at a time

Univalent antigens

In this type of antigen according to valency, in immunological context, it can be used to describe an antigen with a single reactive group

Fab, F(ab')2

Both are antibody fragments that are obtained by the enzymatic digestion of immunoglobulins but they differ in structure and function

Fab

( Fab or F(ab')2 )

Is a monovalent (univalent) fragment consisting of a single light chain homodimer

F(ab')2

( Fab or F(ab')2 )

it lacks the heavy chains

Fab

( Fab or F(ab')2 )

is obtained by papain digestion of IgG, followed by reduction of the light chain disulfide bond

Fab

( Fab or F(ab')2 )

Single antigen-binding sites

F(ab')2

( Fab or F(ab')2 )

Have 2 Ag-binding sites

F(ab')2

( Fab or F(ab')2 )

is a fragment of IgG that is prepared by pepsin digestion of IgG

F(ab')2

( Fab or F(ab')2 )

is the disulfide-linked heterodimer of the 2 light chain dimers, so it retains bivalent epitope binding like whole IgG

F(ab')2

( Fab or F(ab')2 )

it is smaller in size (~110

kDa compare to 150 kDa

for whole IgG)

Fab

( Fab or F(ab')2 )

cannot precipitate or agglutinate

Fab

( Fab or F(ab')2 )

cannot cross-link antigens

F(ab')2

( Fab or F(ab')2 )

can cross-link antigens

F(ab')2

( Fab or F(ab')2 )

contribute to precipitation

and agglutination

Papain

This antibody fragment is obtained by digestion of IgG by what enzyme? Followed by reduction of the light chain disulfide bond

Pepsin

This antibody fragment of IgG is obtained by digestion by what enzyme?

IgG

It is the most abundant type of antibody in the immune system that can enzymatically cleaved by papain and pepsin to produce different fragments

Papain

is a proteolytic enzyme that cuts the IgG molecule above the hinge region

2 Fab, 1 Fc

When IgG is cleaved by Papain, what fragments are produced?

Fab

Each of this fragment from the cleavage of IgG contains a single antigen binding site and it consists of a variable and constant region of a heavy chain.

Fc

This fragment from the cleavage of IgG includes the lower portion of the two heavy chains including the hinge region.

Fc

This antibody region is important for binding to Fc receptors on immune cells and activating the complement. It's more on the factor functions.

Pepsin

It is a proteolytic enzyme that cuts

below the hinge region closer to the Fc part.

Pepsin

When IgG is cleaved by this enzyme, it generates 1 F(ab')2 fragment still connected to the hinge region.

F(ab')2

This antibody fragment, after the cleave of IgG by pepsin, retains the ability to bind to antigen molecules mimicking the intact antibodies by valent binding capacity.

Pepsin

During digestion of IgG using this enzyme, there is no observation of an Fc portion being produced since the Fc portion is degraded by the enzyme into smaller peptides therefore it is no longer functional after the cleavage.

Fc

What antibody fragment from the cleave of IgG by pepsin is degraded by pepsin into smaller peptides therefore it is no longer functional after the cleavage?

Immune complexes

These help in destroying, neutralizing, and eliminating pathogens when they are cross-linked

Immune complexes

They activate the classical complement pathway, leading to pathogen lysis.

Immune complexes

High-density Fc regions on these complexes enhance binding to phagocytes, facilitating antigen removal.

Phagocytosis

What process is involved in cell engulfment and particle digestion that is facilitated by cross-linked immune complexes?

Complement activation

This interaction generates C3b, which binds to immune complexes and helps in their clearance by RBCs and phagocytosis.

C3b Binding

What role of complement involves complement activation generates C3b, which binds to immune complexes and helps in their clearance by RBCs and phagocytosis?

Opsonization

What role of complement involves complement proteins coating the surface of pathogens making it easier for immune cells to recognize and engulf through phagocytosis?

Cell lysis

What role of complement is involved once the complement is activated, there is activation that leads to the formation of the membrane attack complex (MAC)? It makes pores in the pathogen's membrane causing cell lysis

Inflammation

What role of complement involves complement proteins promoting inflammation by recruiting immune cells to the site of infection enhancing the overall immune response?

Precipitation

This occurs when soluble antigens bind with soluble antibodies to form insoluble complexes that precipitate out of solution.

Kraus

Who discovered precipitation in 1897?

Precipitation

It is the combination of soluble antibody with soluble antigen to produce visible insoluble complexes.

Precipitation

In this interaction, when the antigen and antibody are present in optimal proportions, they form visible aggregates or precipitates

Precipitation

This interaction is used to determine the presence of antigens or antibodies in test samples

Affinity

the strength of binding a single antigen and antibody

Affinity

It refers to the initial force of attachment

False

True or False

High affinity forms more unstable antigen-antibody complexes which enhance the likelihood of forming visible precipitates in a reaction

True

True or False

High affinity forms more stable antigen-antibody complexes which enhance the likelihood of forming visible precipitates in a reaction

Affinity

It is the initial strength of attraction between a single Fab site on an antibody and a single epitope (determinant site) on an antigen.

Affinity

This represents the likelihood that the antibody will bind to the antigen based on the complementarity of their shapes, charges and molecular interactions

Avidity

It is the overall binding strength of multiple antigen-antibody interactions

Yes

Yes or No

Is it true that even if individual interactions are weak or low affinity but when combined with high avidity so the interactions can be strong enough to produce a stable complex so there is compensation?

Yes

Yes or No

Higher avidity can increase the efficiency of precipitation.

No

Yes or No

Higher avidity can decrease the efficiency of precipitation.

Law of Mass Action, Principle of Lattice Formation

These principles are related to theoretical conditions of precipitation

Law of Mass Action

Describes the equilibrium between antigen and antibody binding

Law of Mass Action

This law governs the interaction between antigens and antibodies stating that the rate at which these molecules bind is proportional to their concentration

High, Greater

Law of Mass Action

(Low/High) concentration of antigen and antibody increase the likelihood of binding, leading to a (Lesser/Greater) formation of immune complexes

Dissociation

Law of Mass Action

If one component is in excess then the reaction shifts to favor ________ so potentially reducing the effectiveness of precipitation

Principle of Lattice Formation

Refers to the formation of a network like structure of antigen-antibody complexes important for precipitation.

Principle of Lattice Formation

It is the cross-linking of antigens and antibodies into a large stable network

Lattice-like structure

Principle of Lattice Formation

For a visible precipitate to form, multiple binding sites on antibodies must interact with multiple antigen molecules forming a ___________.

Yes

Yes or No

In the Principle of Lattice Formation, optimal proportion of Ag and Ab are necessary for this lattice to form effectively.

No

Yes or No

In the Principle of Lattice Formation, can precipitation happen even if there is too much or too little antigen which causes the lattice formation to be incomplete?

Law of Mass Action, Principle of Lattice Formation

Altogether these principles determine the efficiency and visibility of precipitation reactions by influencing the balance and structure of antigen antibody interaction

Noncovalent bonds

These are bonds that are weak

Ionic bonds

This type of noncovalent bond has attraction between oppositely charged particles such as the positive charge of a basic amino acid and a negative charge of an acidic amino acid

Ionic bonds

This type of noncovalent bond are relatively strong but weaken in the presence of water or high salt concentrations

Electrostatic bonds

Other name for Ionic bonds

Hydrogen bonds

This type of noncovalent bond have attraction between polar molecules with slight charge separation, involving hydrogen atoms.

Hydrogen bonds

This type of noncovalent bond happens when a hydrogen atom is shared between an electron negative atom like oxygen or nitrogen

Hydrogen bonds

This type of noncovalent bond are essential in stabilizing secondary structures like Alpha helices and beta sheets in proteins

Hydrogen bonds

This type of noncovalent bond is really important in proteins

Hydrophobic bonds

This type of noncovalent bond are the association between nonpolar molecules that exclude water.

Hydrophobic bonds

This type of noncovalent bond have regions of molecules aggregate to avoid contact with water

Hydrophobic bonds

This type of noncovalent bond drive the folding of proteins, so in their presence proteins fold and the binding of antigen to antibody in aqueous environment so, largely it can do ours since blood is water based.

Van der Waals bonds

This type of noncovalent bond are interactions between the electron clouds of oscillating dipoles.

Van der Waals bonds

This type of noncovalent bond are weak forces

Van der Waals bonds

This type of noncovalent bond are short range forces that arise from transient dipoles in atoms or molecules

Van der Waals bonds

In this type of noncovalent bond, when molecules are close enough these dipoles induce complementary dipoles in neighboring molecules leading to their attraction

1x10^-7 mm

Noncovalent bonds are relatively weak and act over short distances. What is the approximate distance of the "short distance" referring to?

Yes

Yes or No

Do noncovalent bonds require a very close fit between antigen and antibody for effective binding?

No

Yes or No

Can noncovalent bonds effectively bind if the antigen and antibody are far from each other?

Specificity, Cross-Reactivity, Optimal Binding

What factors are the strength of attraction of noncovalent bonds largely dependent on?

Specificity

The degree to which the antibody binds to a particular antigen depends on the shape and fit of the epitope with the antibody's binding site.

Specificity

This is one of the factors that determines the strength of attraction of noncovalent bonds that largely dependent on the binding of an antibody to a particular antigen as governed by the shape and fit of the antigenic determinant or epitope

Cross-reactivity

It is one of the factors that determines the strength of attraction of noncovalent bonds where antibodies can bind to antigens structurally similar to the original antigen, but the strength of this bond depends on how closely the cross-reacting antigen resembles the original antigen.

Cross-reactivity

It is one of the factors that determines the strength of attraction of noncovalent bonds where structural homology of antigens yet still it is dependent on the point how close a cross reacting Antigen resembles the original antigen