Monoclonal antibodies used in immunotherapy are produced artificially from a cell clone therefore consist of a single type of immunoglobulin. They are targeted towards specific antigens and bind to the antigens to form a complex. The complex can be recognized and destroyed by phagocytes or used for other diagnostic purposes. Natural antibodies are proteins made by the B-lymphocytes in response to antigens. Each B-cell makes only one type of antibody. For therapeutic purposes a significant amount of a particular antibody is needed. These are obtained from a culture that gives a one type of antibody, which are called monoclonal antibodies. CD20 monoclonal antibodies are targeted against B-cell antigens, and are used in the treatment of B-cell Non-Hodgkin’s lymphoma.