What are the functions of immunoglobulin?

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