IMMUNOGLOBULINS
DR. Mohammed Saiemaldahr
FACULTY OF APPLIED MEDICAL
SCIENCES
KAAU
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BIOLOGICAL & CHEMICAL PROPERTIES OF Igs

IgG. Is the major immunoglobulin in human serum, accounting for
approximately 75%. Concentration of approximately 1200 mg/dl.

IgG is a monomer consisting of identical pairs of H and L chains
linked by disulfide bridges.

Four subclasses of IgG have been identified, based on H chain
differences: IgG1, IgG2, IgG3, and IgG4.

IgG is the only immunoglobulin that can cross the placenta in
humans and protect the infant during the first months of life.

IgG molecules are capable of binding complement by the classical
pathway (except for the IgG4, which activate by the alternative
pathway).
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BIOLOGICAL AND CHEMICAL PROPERTIES OF IMMUNOGLOBULINS

IgG is the major antibody produced in the secondary
immune response

IgG has a half-life of approximately 21 days

Effective antitoxic immunity is exclusively IgG.

IgG is the major opsonizing immunoglobulin in
phagocytosis; neutrophils have receptors for the Fc
fragments of IgGI and IgG3.
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BIOLOGICAL & CHEMICAL PROPERTIES OF Igs

IgM. Represents about 8% to 10% of the total serum Igs .
Concentration of ≈ I2O mg/dl.

IgM has a pentameric structure consisting of five monomer units
linked by a J chain and by disulfide bonds at the Fc fragment.

IgM is easily dissociated by reducing agents, forming five
monomeric units.
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BIOLOGICAL AND CHEMICAL PROPERTIES OF IMMUNOGLOBULINS

IgM is the first antibody that an immunologically committed B
lymphocyte can produce. It has a half-life of approximately 10
days.

IgM is the predominant antibody in the early (primary) immune
response to most antigens.

IgM is the only antibody made to certain carbohydrate antigens,
such as the ABO blood group antigens on human erythrocytes.

IgM is the most efficient immunoglobulin at activating
complement in lytic reactions.
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Allo-antibodies & Auto-antibodies

Antigens that initiate the immune cascades results in the
formation of either allo-abs or auto-abs.

Allo-antibodies are produced after exposure to genetically
different or non-self, antigens of the same species.

Auto-antibodies are produced in response to self antigens.
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Factors Influence Agglutination Reaction
Concentration of Ag-Ab
The agglutination reaction is influenced by the,
concentration of both Ag and Ab as well as other factors such as pH,
temp. ionic strength, surface change, Ab class, red cell Ag dosage, the
use of various enhancement media

Under ideal reaction conditions, an equivalent amount of Ag and
Ab bind in optimal proportions.

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Factors Influence Agglutination Reaction

Prozone effect: an excess of either Ag or Ab, may lead to unbound
immunoglobulin

Postzone effect: surplus (excess of Ag-binding sites)
In prozone or postzone effect the lattice formation and subsequent
agglutination may not occur in the test system, leading to the
assumption of false negative results.

To correct the problem of excessive Ab, the serum may be diluted with
each serial dilution of serum tested against red cells.

To correct the problem of excessive Ag, the serum to cell-ratio in the test
system may be in which will tend to increase the number of Abs
available to bind with red cell.
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Factors Influence Agglutination Reaction

Effect of pH
The ideal pH is between 6.5 and 7.5, exceptions to this range include
some examples of Anti-M, and some Abs of the Pr (SP1) group
which show stronger reactivity below pH 6.5.
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Factors Influence Agglutination Reaction

Temperature
Different types of Abs may exhibit optimal reactivity at different
temp.
IgM Abs usually react optimally at or below 22°C.
IgG Abs usually require 37°C temp.
The Ag-Ab reactions are exothermic (heat is given up), therefore,
Abs binds to a greater degree at low temperature
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Laboratory Examination of Reaction between Ags and Abs

In vitro testing for the detection of Ags or Abs may be
accomplished by a variety of immunologic techniques. Such
techniques as agglutination, precipitation, agglutination
inhibition, and hemolysis are the most commonly used methods
to detect the presence of blood group Ags or Abs.

In blood bank testing, agglutination reactions are the major
manifestation of the blood group Ag-Ab response. Typing for
ABO, Rh, and other blood group Ags is accomplished by
agglutination reaction.
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Laboratory Examination of Reaction between Ags and Abs

There are two stages for agglutination to develop;

Stage 1: known as sensitization, Ab binding occurs. Antigenic
determinants on the red cell membrane combine with the
antigen combining site (Fab region) on the variable regions of the
immunoglobulin heavy and light chains.

Stage 2: a lattice structure composed of multiple Ag-Ab bridges
between Abs and red cell Ags is formed visible agglutination is
present during this stage.
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