15) The core of adaptive immunity: immunoglobulin antibodies

The immune system depends on special binding molecules known as immunoglobulins, also referred to as "antibodies" or "Ig" for short. Immunoglobulins are "Y" shaped molecules that connect on one end to invading microbes (antigens) and on the other end they bind with various white cells that effectivley block and destroy the antigen. These specialized antibody molecules come in different shapes and sizes in order to provide flexibility in matching and destroying targeted antigens. Antibody molecules are found floating in the plasma as well as on the surface of specialized B-cells.

Immunoglobulins are constructed from two types of amino acid chains, heavy chains and light chains. Ig molecules contain two identical strands of heavy chains and two identical strands of light chains. The end with the two heavy chains forms a stable non-variable receptor point called an effector, which is the part of the Ig molecule that binds with our own immune system cells.

On the opposite end of the antibody are two antigen binding sites, each with a light chain and heavy chain combination. This combination of light and heavy chains forms highly variable tips that can adapt to match a specific antigen.

Immunoglobulins come in five basic types: IgA, IgD, IgE, IgG and IgM. Each type targets a specific type of antigen, which determines the make-up of the Y chain structure of each.

IgD, IgE and IgGs all use a single Y chain whether as stand alone antibodies or as receptors connected to white cells.

IgAs use a double Y chain, called a Dimer.

IgMs are unique in that they form a single Y chain when expressed on the surface of a B-cell, but the stand alone version of the IgM molecule forms a combination of five Y chains, known as a pentamer. Consequently, stand alone IgMs form a very large antibody molecule.