Antibodies in human immune system

An antibody, also known as an immunoglobulin, is a large Y-shaped protein produced by B cells (specialized white blood cells). When an antigen comes into contact with a B cell, it causes the B cell to divide and clone. These cloned B cells — or plasma cells — release millions of antibodies into human bloodstream and lymph system.

Antigens are large molecules (usually proteins) on the surface of cells, viruses, fungi, bacteria, and some non-living substances such as toxins, chemicals, drugs, and foreign particles. The immune system recognizes antigens and produces antibodies that destroy substances containing antigens.

Antibodies are located in various areas of human body, including skin, lungs, tears, saliva and even breast milk. In fact, high amounts of antibodies are present in colostrum.

Antibodies play a crucial role during the humoral immunity by attacking or eliminating pathogenic bacteria or viruses as foreign substances when they invade the body. Antibody functions include neutralization of infectivity, phagocytosis, antibody-dependent cellular cytotoxicity (ADCC), and complement-mediated lysis of pathogens or of infected cells.

Antibodies are categorized into five classes according to their location: IgA, IgD, IgE, IgG, IgM. They are distributed and function differently in the body.
Antibodies in human immune system