Antibody

Introduction

An Antibody is a large, Y-shaped protein produced mainly by plasma cells that is used by the immune system to neutralize pathogens such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the pathogen, called an Antigen, via the Fab's variable region. Each tip of the "Y" of an antibody contains a paratope (analogous to a lock) that is specific for one particular epitope (similarly analogous to a key) on an antigen, allowing these two structures to bind together with precision.

Structure

Antibodies are heavy (~150 kDa) globular plasma proteins. They have sugar chains added to some of their amino acid residues, a process called glycosylation. Glycosylation of antibodies in this manner has been thought to change the protein's physical and biological properties. Each immunoglobulin molecule is composed of four polypeptides—two heavy chains and two light chains. Both the heavy and light chains of the antibody have constant and variable regions.

Classes of Antibodies

There are five different types of mammalian antibodies known as isotypes or classes. In placental mammals, they are: IgA, IgD, IgE, IgG, and IgM. Each isotype is differentiated by its biological properties, functional locations, and ability to deal with different antigens.

Mechanism of Action

Antibodies can bind to a wide variety of antigens, and the way they help to clear those antigens from the organism can differ, which can be broadly divided into direct and indirect mechanisms of action.

Antibody Production and Regulation

The production of antibodies is a complex process, involving both the innate and adaptive immune systems, and is regulated by a variety of mechanisms. Antibodies are produced by B cells, which are activated upon recognition of antigen.

Clinical Significance

Antibodies have a central role in the immune response, and their importance is reflected in many aspects of medicine and clinical practice. They are used in a variety of diagnostic tests, and are increasingly being used as therapeutic agents in a number of conditions.