Immunoglobulins are glycoprotein molecules. Both function as antibodies and are produced by plasma cells in response to an antigen. These are some of the key functions of immunoglobulins: 

• Protect the host by identifying and binding to a specific antigen or a few closely related antigens
• Activate the immune system in case of bacterial pathogens
• Provide the first line of defense for mucosal surfaces 
• Attack viral pathogens directly and immediately
• Assist in phagocytosis
• Provide long-term protection against pathogens by their ability to persist for several years after the pathogen invasion