Definition of Ig

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Ig: Abbreviation for immunoglobulin, a protein produced by plasma cells and lymphocytes. Immunoglobulins are an essential part of the body's immune system which attach to foreign substances, such as bacteria, and assist in destroying them.

The classes of immunoglobulins are immunoglobulin A (IgA), immunoglobulin G (IgG), immunoglobulin M (IgM), immunoglobulin D (IgD) and immunoglobulin E (IgE).