Here is a good multi-part question from a student trying to understand some things about myeloma.
Q. First, when you talk about monoclonal immunoglobulin, is it always exactly the same antibody for only one antigen? Or is it just the same type ( IgG kappa, IgM kappa, etc..) but not exactly the same same same?
A. Good question. I like the way you put that – the “same same same” antibody. Yes: when there is a monoclonal immunoglobulin spike, the antibodies (immunoglobulins) are not only of the same type (also called “isotype” or “class”) of heavy and light chain (IgG and kappa, for example) – but they also have the same idiotype (meaning they are directed against exactly the same antigen, or “epitope”). This means that the part of the antibody way at the end of the variable region (circled and labeled “1” in the diagram above) – the part that actually binds to the antigen – is exactly the same. See this post on antibody isotypes, idiotypes and allotypes for more information on the wording.
Q. Also why is this proliferation bad for the body? How does it “kill” it?
A. The antibodies in and of themselves are usually not a huge problem (though sometimes they end up reacting with other things in the body – like red cell antigens – which can create problems – like hemolytic anemia). The big problem is that for some reason, normal immunoglobulin production is decreased. Somehow, the tumor cells communicate with normal plasma cells and tell them to stop making so much immunoglobulin. In fact, the most common cause of death in patients with multiple myeloma is infection.
Q. And what is the difference between myeloma and multiple myeloma? Is it the same?
A. Yes – multiple myeloma and myeloma refer to the same disease. The disease was named multiple myeloma because patients have many (“multiple”) different tumors in the bone marrow (“myelomas”).
Q. In my book it says antibodies have two light chains and two heavy chains. But i see you say it’s one heavy and one light. So is my book wrong?
A. No! It is correct! Antibodies are composed of two light chains and two heavy chains (check out the image, above: two blue heavy chains and two yellow light chains). What I meant was that antibodies have one type of light chain (for example, kappa) and one type of heavy chain (for example, IgG).