Plasma cells come from B cells, which circulate in the body until they find a specific substance. Then, they go into a maturation process and become plasma cells. These plasma cells live in the bone marrow and produce antibodies (also called immunoglobulins) that fight various infections, among other things, such as cancer. 

In normal circumstances, plasma cells produce antibodies compromising two parts: heavy chains and light chains. These two parts are combined together and secreted into the blood and other places in the body. In addition, plasma cells secrete a small number of light chains that are not attached to the heavy chain (also called free light chains). 

In myeloma, plasma cells grow out of control in the bone marrow, crowding out the other cells of the bone marrow. Also, this abnormal plasma cell population (monoclonal plasma cells) secrete excessive heavy chains and light chains (monoclonal protein or m-spike), including the complete immunoglobulin and/or the free light chains. Consequently, other immunoglobulins secreted by normal plasma cells are reduced, leading to a deficient immune system. 

What Are Light Chains? 

There are two types of light chains: kappa and lambda. If a patient has kappa myeloma, their doctor will watch for a rise in the kappa numbers. Likewise, the lambda number will be watched if a patient has lambda myeloma. This can be measured by the Free Light Chain Assay test on a blood or urine specimen. This balance of kappa and lambda together is called the kappa/lambda ratio, which can also indicate a change in levels of disease. "The ratio or proportion between the kappa and lambda light chains indicates an excess production of one chain over the other, and therefore can be used as an indication of disease progression or remission," said Dr. Christina Gasparetto of Duke University.