An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses
Structure
• Immunoglobulin domains
• Heavy chain
• Light chain
• CDRs, Fv, Fab and Fc Regions
there are five antibody isotypes known as IgA, IgD, IgE, IgG and IgM
Antibody isotypes of mammals




IgA
mmunoglobulin A (IgA) is an antibody that plays a critical role in mucosal immunity. More IgA is produced in mucosal linings than all other types of antibody


1. Structure
Serum IgA is a monomer but IgA found in secretions is a dimer. When IgA exits as a dimer, a J chain is associated with it.
When IgA is found in secretions is also has another protein associated with it called the secretory piece or T piece; sIgA is sometimes referred to as 11S immunoglobulin. Unlike the remainder of the IgA which is made in the plasma cell, the secretory piece is made in epithelial cells and is added to the IgA as it passes into the secretions (Figure 12). The secretory piece helps IgA to be transported across mucosa and also protects it from degradation in the secretions.
2. Properties
a) IgA is the 2nd most common serum Ig.
b) IgA is the major class of Ig in secretions - tears, saliva, colostrum, mucus. Since it is found in secretions secretory IgA is important in local (mucosal) immunity.
c) Normally IgA does not fix complement, unless aggregated.
d) IgA can binding to some cells - PMN's and some lymphocytes.
3.IgA Subclasses
a) IgA1 - Alpha 1 heavy chains: IgA1 is the predominant IgA subclass found in serum. Most lymphoid tissues have a predominance of IgA-producing cells
b) IgA2 - Alpha 2 heavy chains: In IgA2, the heavy and light chains are not linked with disulfide, but with noncovalent bonds. In secretory lymphoid tissues (e.g. gut associated lymphoid tissue, GALT), the share of IgA2 production is larger than in the non-secretory lymphoid organs (e.g. spleen, peripheral lymph nodes).
1. Increases in:
a) Wiskott-Aldrich syndrome
b) Cirrhosis of the liver (most cases)
c) Certain stages of collagen and other autoimmune disorders such as rheumatoid arthritis and lupus erythematosus
d) Chronic infections not based on immunologic deficiencies
e) IgA myeloma
2. Decreases in:
a) Hereditary ataxia telangiectasia
b) Immunologic deficiency states (e.g., dysgammaglobulinemia, congenital and acquired agammaglobulinemia, and hypogammaglobulinemia)
c) Malabsorption syndromes
d) Lymphoid aplasia
e) IgG myeloma
f) Acute lymphoblastic leukemia
g) Chronic lymphoblastic leukemia
IgE


Immunoglobulin E (IgE) is a protein called an antibody that is produced by B-lymphocytes. IgE is primarily involved in the allergic response. When a patient is first exposed to an allergen, some of these B-cells are activated and begin to secrete immunoglobulin E. This IgE binds to the surface of mast cells and basophils.
1. Structure. IgE exists as a monomer and has an extra domain in the constant region.
2. Properties
a) IgE is the least common serum Ig since it binds very tightly to Fc receptors on basophils and mast cells even before interacting with antigen.
b) Involved in allergic reactions - As a consequence of its binding to basophils an mast cells, IgE is involved in allergic reactions. Binding of the allergen to the IgE on the cells results in the release of various pharmacological mediators that result in allergic symptoms.
c) IgE also plays a role in parasitic helminth diseases. Since serum IgE levels rise in parasitic diseases, measuring IgE levels is helpful in diagnosing parasitic infections. Eosinophils have Fc receptors for IgE and binding of eosinophils to IgE-coated helminths results in killing of the parasite.
d) IgE does not fix complement.
1. Increases in:
a) Atopic skin diseases such as eczema
b) Hay fever
c) Asthma
d) Anaphylactic shock
e) IgE-myeloma
2. Decreases in:
a) Congenital agammaglobulinemia
b) Hypogammaglobulinemia due to faulty metabolism or synthesis of immunoglobulins
References
http://en.wikipedia.org/wiki/Antibody
http://pathmicro.med.sc.edu/mayer/IgStruct2000.htm
Video
The Immune Response
http://www.youtube.com/watch?v=G7rQu...18C93964A61F67
Anaphylactic allergic reaction
http://www.youtube.com/watch?v=olFD1...eature=related