Antibodies. Computer artwork of antibody, or immunoglobulin, molecules and a plasma cell (bottom left). Plasma cells are mature B lymphocytes (white blood cells) that produce and secrete antibodies during an immune response. The y-shaped antibody molecules have two arms that can bind to specific antigens, for instance viral or bacterial proteins. In doing this they mark the antigen for destruction by phagocytes, white blood cells that ingest and destroy foreign bodies. Antibodies can also kill some pathogens directly and can neutralise toxins.