ANTIBODIES

Antibodies are immunoglobulin (20% of the total plasma proteins) and synthesized and secreted by the plasma cells. Antibodies have a divers group of functions in the adaptive immune response. Antibodies,

Detoxify toxins

Prevent the adherence of pathogenic organisms to mucosal surfaces.

Opsonizes

Fix complement

There are five types of antibodies. IgG, IgA, IgM, IgD, IgE

Usually antibodies are made up of light and heavy protein chains. Amino terminal of the heavy and light chains make up the antigen binding site. Simplest antibody molecule has a “Y “shape.

IgG

Predominant antibody in the secondary immune response.

Can cross the placental barrier. So the most predominant antibody in the newborn.

Molecular formula is H2L2 (H- heavy chain, L- light chain)

Divalent – has two antigen binding sites.

IgM

Major antibody produced early in the primary immune response.

IgM present on all uncommitted B cell surfaces.

Molecular formula 5(H2L2)

Valancy = 10

Most efficient is agglutination, complement fixation.

IgA

Major antibody found in milk, saliva, tears, respiratory tract secretions, G.I.T. secretions and genital tract secretions.

Stop the invasion of the pathogens through the mucosal surfaces.

Molecular formula = 2(H2L2)

IgE

Fc portion has a high affinity for receptors on mast cell membrane. When an antigen binds to the Fab portion of IgE it causes degranulation of the mast cell. This initiate an acute inflammatory response.

IgD

Mainly present on the B cell surfaces

Only trace amounts in the plasma.