Ig G structure, role and properties

1. IMMUNOGLOBULIN G
STRUCTURE & PROPERTIES

2. CONTENT
 GENRAL INTRODUCTION
 STRUCTURE
 FUNCTION
 SUBCLASSES OF Ig G
 DEFICIT OF Ig G

3. GENERAL INTRODUCTION
Fundamental roles: Key player in the humoral immune response. Can activate the
complement system. Phagocytosis of microorganisms.
Found in : the major immunoglobulin in blood, lymph fluid, cerebrospinal fluid, and
peritoneal fluid.
Reacts with: macrophages, neutrophils, natural killer (NK) cells.
Presence in serum: makes up approximately 15% of total proteins in healthy
humans.

4. STRUCTURE
 composed of 82 - 96% protein and 4 - 18%
carbohydrate.
 150 kDa made of four peptide chains.
 It contains two identical class heavy chains of
about 50 kDa and two identical light chains of
about 25 kDa
 The two heavy chains are linked to each other
and to a light chain each by disulphate bond.
 The resulting tetramer has two identical halves,
which together form the Y-like shape.
 Each end of the fork contains an
identical antigen binding site.

5. Subclasses of Ig G

6. FUNCTION
 IgG protects the body from infection.
 IgG-mediated binding of pathogens causes their immobilization and binding
together via agglutination opsonisation activates the classical pathway of
the complementary system a cascade of immune protein production that results in
pathogen elimination.
 IgG also binds and neutralizes toxins.
 IgG also plays an important role in antibody dependent cell mediated cytotoxicity
(ADCC).
 IgG are also involved in the regulation of allergic reactions

7.  IgG is secreted as a monomer that is small in size allowing it to easily perfuse
tissues. It is the only isotope that has receptor to facilitate passage through the
human placenta, thereby providing protection to the foetus in utero.
 Along with IgA secreted in the breast milk, residual IgG absorbed through the
placenta provides the neonate with humoral immunity before its own immune
system develops.
 Colostrum contains a high percentage of IgG, especially bovine colostrum.

8. DEFICIT OF Ig G
 IgG2 or IgG3 deficiencies are the most common IgG subclass deficiencies. Since
IgG1 comprises 60% of the total IgG level, deficiency of IgG1 usually drops the total
IgG level below the normal range, resulting in hypogammaglobulinemia.
 IgG4 is present in very low levels in children younger than 10 years of age, so IgG4
deficiencies are not usually diagnosed before age 10.

9. SYMPTOMS
 Sinus infections and other respiratory infections
 Gastrointestinal infections
 Ear infections
 Pneumonia
 Bronchitis
 Infections that result in sore throat
 Rarely, severe and life-threatening infections
 In some people, infections cause scarring that harms the airways and lung function.
This can affect breathing. People with IgG deficiency also often find that pneumonia
and the flu vaccines don’t keep them from getting these infections.

10. CLINICAL DIAGNOSIS
 A blood test that measures immunoglobulin levels can diagnose IgG deficiency.’
 It’s possible to have a normal level of total IgG, so the testing of the IgG subclasses
is important.
 Tests can also be done on saliva and cerebrospinal fluid. But, a blood test is the
most common.