Immunoglobulin G antibody. Molecular model of part of an immunoglobulin G (IgG) antibody. It depicts the 3-dimensional structures present in the protein chains that make up the antibody molecule. Each cylinder represents a helical structure, or alpha helix, and each group of arrows represents a structure known as a beta sheet. Antibodies defend the body against infection. The region seen here is one of two branched regions that bind foreign proteins, neutralising their activity or initiating immune reactions against them. IgG antibodies are produced by B-lymphocyte blood cells and are found in the liquid plasma component of the blood.