What are the similarities between immunoglobulin and antibody?

Immunoglobulin and antibody are both disease-fighting glycoproteins that play important roles in protecting the body from pathogens. Both are produced by plasma cells in the immune system of most vertebrates in response to the presence of an antigen. 

Immunoglobulin and antibodies have several structural similarities too. Both are made up of heavy and light chains and both have constant and variable regions.