Immunoglobulins

Immunoglobulins (Igs), also known as antibodies, are produced by plasma cells. They identify and mark foreign invaders such as bacteria and viruses for removal or destruction by other cells of the immune system.

Each Ig binds only to the specific antigen that induced its production. This characteristic is called ‘antibody specificity’ and means that antibodies are produced in a specialised molecular shape that will bind only to the targeted antigen, similar to a lock and key mechanism (Figure 4).

Figure 4: Immunoglobulin (antibody) binding to antigen

Normally, Igs produced by plasma cells are polyclonal, meaning they are made by numerous plasma cells derived from many precursor cells. In the case of myeloma, the abnormal plasma cells are all derived from a single precursor cell and produce only one specific or monoclonal Ig. This monoclonal Ig is also referred to as paraprotein, M protein or M-spike.  The level of paraprotein is often used as an indication of the activity of the myeloma.

Paraproteins are different from normal antibodies produced by healthy plasma cells because they are of no functional use. In addition, myeloma cells crowd out other cells in the bone marrow including normal functional plasma cells, leaving the immune system unable to produce enough Igs and other immune cells to fight infection. Consequently, many myeloma patients become severely immunosuppressed.