Chapter 10: Serology Concepts

Immunogen

Immunogen

A foreign substance that is capable of eliciting antibody formation when introduced into a host.

Natural immunogens

are usually macromolecules such as proteins and polysaccharides.

Epitope

Also known as determinant site; the molecular structure of an immunogen, usually a small portion recognized by an antibody.

Multivalent

Multiple epitope in an immunogen.

Antigen

A foreign substance that is capable of reacting with an antibody.

Hapten

An example of a substance that is antigenic but not immunogenic.

Antibodies

Also known as immunoglobulins, are capable of binding specifically to antigens and are designated with an Ig prefix.

Isotypes

The immunoglobulins that differ based on the molecular variations in the constant domains of the heavy and light chains.

IgD, IgE, and IgG

are usually monomers.

IgM

can be a membrane-bound monomer or a cross-linked pentamer.

IgA

can be a monomer, dimer, or trimer.

IgG

is the most abundant immunoglobulin in serum.

H chain

The _____ can be divided into fragment antigen-binding (Fab) and fragment crystallizable (Fc) fragments.

L chain

The _____ consists of a Fab fragment only.

bivalent

A typical antibody has two identical antigen-binding sites and is thus considered ______.

variable and constant domains

At the amino acid sequence level, both H and L chains have _____.

N-terminal

The variable domains are located at the _______ ends of the immunoglobulins.

immunogen

To produce an antibody, an _______ is usually introduced into a host animal.

multivalent immunogen

A ________ is capable of eliciting a mixture of antibodies with diverse specificities for the immunogen.

polyclonal antibody

As a result, a ______ is produced by different B lymphocyte clones in response to the different epitopes of the immunogen.

Humoral Antibodies

Circulating immunoglobulins.

serum

The blood from an immune host is drawn and allowed to clot, resulting in the formation of a solid consisting largely of blood cells and a liquid portion known as _____ containing antibodies.

Polyclonal Antiserum

Preparation of humoral antibodies.

spleen cells

To produce a monoclonal antibody, ______ are harvested from a host animal, such as a mouse, inoculated with an immunogen.

myeloma

Next, the plasma cells of the spleen, which produce antibodies, are fused with ______ cells.

hybridoma cells

The fused cells, called ______, are immortal in cell cultures.

antiglobulins

If a purified foreign immunoglobulin or a fragment of a foreign immunoglobulin is introduced into a host, the antibodies produced are known as ________.

Noncovalent bonds

can be formed during antigen–antibody binding.

Affinity

The energy of the interaction of a single epitope on an antigen and a single bind- ing site on a corresponding antibody.

Cross-reaction

Antibodies bind with lower strength to antigens that are structurally similar to the immunogen.

Avidity

The overall strength of the binding of an antibody and an antigen.

Primary Reactions

It is the binding of a single epitope of an antigen (Ag) and a single binding site of an antibody (Ab) to form an antigen–antibody complex.

Precipitation

If a soluble antigen is mixed and incubated with its antibody, the antigen–antibody complexes can form cross-linked complexes at the optimal ratio of antigen-to-antibody concentration.

Precipitins

Antibodies that produce such precipitation.

Precipitin Curve

Illustrates the results observed when antigens and antibodies are mixed in various concentration ratios.

Prozone

Here the ratio of antigen–antibody concentration is low.

The Zone of Equivalence

As the concentrations of antigen increase, the amount of precipitate increases until it reaches a maximum.

Postzone

Here the ratio of antigen–antibody concentrations is high or in excess.

Agglutination

If the antigens are located on the surfaces of cells or carriers antibodies can bind to the surface antigens and can form cross-links among cells or carriers, causing them to aggregate.

hemagglutination

If the antigen is located on an erythrocyte, the agglutination reaction is designated _________.

Initial Binding

The first step of the reaction involves antigen–antibody binding at a single epitope on the cell surface.

Lattice Formation

The second step involves the formation of a cross-linked network resulting in visible aggregates that constitute a lattice.

Agglutinins

Antibodies that produce agglutination.

Complete Antibody

Capable of carrying out both primary and secondary interactions that result in agglutination.

Incomplete Antibody

An antibody that can carry out initial binding but fails to form agglutination.