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IMMUNOGLOBULINS
Immunoglobulin Classes
I. IgG
Structure: Monomer (m.wt 150,000)
Percentage serum antibodies: 75-80%
Is the major Ig in extra vascular spaces
Location: Blood, lymph, intestine
Half-life in serum: 23 days
Complement Fixation: Yes (IgG4 does
not
fix
complement.)
Placental Transfer: Yes
Known Functions:is the most versatile immunoglobulin,
because it is capable of carrying out all of the functions of IG
molecules:
•Enhances phagocytosis
•Neutralizes toxins and viruses,
•Protects fetus and newborn.
IgG
II. IgM
Structure: Pentamer (m.wt 900,000)
Has an extra domain on the μ chain (CH4) & it has
another protein covalently bound via an S-S bond
called the J chain, This chain functions in
polymerization of the molecule into a pentamer
 Percentage serum antibodies: 5-10%
Location: Blood, lymph
Half-life in serum: 5 days
Complement Fixation: Yes
Placental Transfer: No
Known Functions:
• First antibodies produced during an infection.
• Effective against microbes and agglutinating
antigens.
III. IgA
Structure: Dimer (m.wt 150,000-350,000)
When IgA exits as a dimer, a J chain is associated
with it.
Percentage serum antibodies: 10-15%
Location: Secretions (tears, saliva, intestine, milk),
blood and lymph.
Half-life in serum: 6 days
Complement Fixation: Normally does not fix
complement, unless aggregated.
Placental Transfer: No
Known Functions:
•Localized protection of mucosal surfaces.
•Provides immunity to infant digestive tract.
IV. IgD
u
u
u
u
u
u
u
Structure: Monomer (m.wt 180,000)
Percentage serum antibodies: 0.2%
Location: B-cell surface, blood, and lymph
Half-life in serum: 3 days
Complement Fixation: No
Placental Transfer: No
Known Functions: In serum function is unknown. On B cell
surface, initiate immune response.
V. IgE
u Structure: Monomer(m.wt 190,000)
u Percentage serum antibodies: 0.002%
u IgE is the least common serum Ig since it binds very
tightly to Fc receptors on basophils & Mast cells even
before interacting with Ag.
u Location: Bound to mast cells and basophils
throughout body.
u Half-life in serum: 2 days
u Complement Fixation: No
u Placental Transfer: No
u Known Functions: Allergic reactions. Possibly lysis of
worms.
CLINICAL IMPLICATIONS OF HUMAN
IMMUNOGLOBULIN CLASSES
IgG
Increases in:
1) Chronic granulomatous
infections.
2) Infections of all types.
3) Hyperimmunization.
4) Liver disease.
5) Severe Malnutrition.
6) Dysproteinemia.
7) Rheumatoid arthritis.
Decreases in:
1) Agammaglobulinemia.
2) Lymphoid aplasia.
3) Selective IgG & IgA
deficiency
4) IgA myeloma.
5) Bence Jones proteinemia.
6) Chronic lymphocytic
leukemia.
IgM
IgM increases (in newborns)
- A level of IgM above 20
mg/dl is an indication of in
utero infection:
1)- rubella virus.
2)- cytomegalovirus.
3)- syphilis.
4)- toxoplasmosis.
IgM increases (in adults) in:
1) Waldenström’s
macroglobulinemia.
2) Trypanosomiasis.
3) Actinomycosis.
4) Malaria
5)Infectious mononucleosis.
6) Lupus erythematosus.
7) Rheumatoid arthritis.
IgM decreases in:
1) Agammaglobulinemia.
2). Lymphoid aplasia.
3) IgG & IgA myeloma.
4) Dysgammaglobulinemia.
5) Chronic lymphocytic leukemia.
IgA
IgA increases in:
1) Wiskott-Aldrich syndrome.
2) Most cases of liver
Cirrhosis
3) Certain stages of collagen
& other autoimmune
disorders such as
rheumatoid arthritis & lupus
erythematosus.
4) IgA myeloma.
IgA decreases in:
1) Hereditary ataxia
telangiectasia.
2) Immunologic deficiency
states
(e.g.:dysgammaglobulinemi
a, congenital & acquired
agammaglobulinemia, &
hypogammaglobulinemia).
3) Malabsorption syndromes.
4) Lymphoid aplasia.
5) IgG myeloma.
6) Acute & Chronic
lymphoblastic leukemia.
IgD increases in:
1) Chronic infections.
2) IgD myelomas.
IgE increases in:
1) Atopic skin diseases such as eczema.
2) Hay fever.
3) Asthma.
4) Anaphylactic shock.
5) IgE-myeloma.
IgE decreases in:
- Congenital agammaglobulinemia
Immunoglobulin Structure
Disulfide bond
Carbohydrate
CL
VL
CH2
CH1
VH
Hinge Region
CH3