Immunoglobulins (Igs) are proteins contributing to immunity mechanisms. Immunity is specific to the lymphoid system, which consists of organs (spleen, thymus, bone marrow) and cells (lymphocytes). Immunoglobulins are secreted by B lymphocytes in the blood, and in this way are exported for the specific functions of humoral immunity.
Immunoglobulin G (IgG) is the main Ig synthesised by plasma cells, representing 70-75% of immunoglobulins. IgG antibodies are produced in response to most bacteria and viruses, and assist in destruction of the latter: they are therefore of particular importance in the long-term defence of the human body against infection.