Antibodies, also known as immunoglobulins, are Y-shaped proteins produced by plasma cells that are involved in the immune response. They are composed of two light chains and two heavy chains that give them a flexible structure allowing them to recognize and bind to foreign objects like bacteria and viruses. There are five main classes of antibodies - IgG, IgA, IgM, IgE, and IgD - that carry out different functions in the immune system such as neutralizing toxins, marking pathogens for destruction, and activating immune cells.