IMMUNOGLOBULINS

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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
  22C.
• IgG Abs usually require 37C 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.